Tree geometry-initialization simplifications for 4.3
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cover Tree geometry-initialization simplifications for 4.3
Hello!
This series simplifies the arithmetic involved in computing the geometry of Tree RCU's combining tree.
1. Provide more diagnostics for stalled GP kthread. (A bit off-topic,
but included in this series due to conflicting updates.)
2. Panic if RCU tree can not accommodate all CPUs, courtesy of
Alexander Gordeev.
3. Remove superfluous local variable in rcu_init_geometry(),
courtesy of Alexander Gordeev.
4. Cleanup rcu_init_geometry() code and arithmetic, courtesy of
Alexander Gordeev.
5. Simplify rcu_init_geometry() capacity arithmetic, courtesy of
Alexander Gordeev.
6. Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items, courtesy of
Alexander Gordeev.
7. Limit rcu_capacity[] size to RCU_NUM_LVLS items, courtesy of
Alexander Gordeev.
8. Remove unnecessary fields from rcu_state structure, courtesy of
Alexander Gordeev.
9. Limit count of static data to the number of RCU levels, courtesy
of Alexander Gordeev.
10. Simplify arithmetic to calculate number of RCU nodes, courtesy
of Alexander Gordeev.
11. Shut up bogus gcc array bounds warning, courtesy of Alexander
Gordeev.
12. Reset rcu_fanout_leaf if out of bounds.
Thanx, Paul
------------------------------------------------------------------------
b/kernel/rcu/tree.c | 156 +++++++++++++++++++++------------------------ b/kernel/rcu/tree.h | 45 +++++++----- b/kernel/rcu/tree_plugin.h | 4 - 3 files changed, 103 insertions(+), 102 deletions(-)
PATCH 1/12 rcu: Provide more diagnostics for stalled GP kthread
From: "Paul E. McKenney" <[email protected]>
--- kernel/rcu/tree.c | 10 ++++++++-- kernel/rcu/tree.h | 6 +++++- 2 files changed, 13 insertions(+), 3 deletions(-)
kernel/rcu/tree.c +8 -2
@@ -1178,9 +1178,11 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp) j = jiffies; gpa =READ_ONCE (rsp->gp_activity);if (j - gpa >2 *HZ ) -pr_err ("%s kthread starved for %ld jiffies! g%lu c%lu f%#x\n" , +pr_err ("%s kthread starved for %ld jiffies! g%lu c%lu f%#x s%d ->state=%#lx\n" , rsp->name, j - gpa, - rsp->gpnum, rsp->completed, rsp->gp_flags); + rsp->gpnum, rsp->completed, + rsp->gp_flags, rsp->gp_state, + rsp->gp_kthread ? rsp->gp_kthread->state :0 ); }/*
@@ -2041,6 +2043,7 @@ static int __noreturn rcu_gp_kthread(void *arg)wait_event_interruptible (rsp->gp_wq,READ_ONCE (rsp->gp_flags) &RCU_GP_FLAG_INIT ); + rsp->gp_state =RCU_GP_DONE_GPS ;/* Locking provides needed memory barrier. */ if (rcu_gp_init (rsp))break ;
@@ -2073,6 +2076,7 @@ static int __noreturn rcu_gp_kthread(void *arg) (!READ_ONCE (rnp->qsmask) && !rcu_preempt_blocked_readers_cgp (rnp)), j); + rsp->gp_state =RCU_GP_DONE_FQS ;/* Locking provides needed memory barriers. */ /* If grace period done, leave loop. */ if (!READ_ONCE(rnp->qsmask) &&
@@ -2110,7 +2114,9 @@ static int __noreturn rcu_gp_kthread(void *arg) }/* Handle grace-period end. */ + rsp->gp_state =RCU_GP_CLEANUP ;rcu_gp_cleanup (rsp); + rsp->gp_state =RCU_GP_CLEANED ; } }
kernel/rcu/tree.h +5 -1
@@ -527,7 +527,11 @@ struct rcu_state {/* Values for rcu_state structure's gp_flags field. */ #define RCU_GP_WAIT_INIT 0/* Initial state. */ #define RCU_GP_WAIT_GPS 1/* Wait for grace-period start. */ -#define RCU_GP_WAIT_FQS 2/* Wait for force-quiescent-state time. */ +#define RCU_GP_DONE_GPS 2/* Wait done for grace-period start. */ +#define RCU_GP_WAIT_FQS 3/* Wait for force-quiescent-state time. */ +#define RCU_GP_DONE_FQS 4/* Wait done for force-quiescent-state time. */ +#define RCU_GP_CLEANUP 5/* Grace-period cleanup started. */ +#define RCU_GP_CLEANED 6/* Grace-period cleanup complete. */ extern struct list_head rcu_struct_flavors;
Signature · 1 line
1.8.1.5
PATCH 2/12 rcu: Panic if RCU tree can not accommodate all CPUs
From: Alexander Gordeev <[email protected]>
Currently a condition when RCU tree is unable to accommodate the configured number of CPUs is not permitted and causes a fall back to compile-time values. However, the code has no means to exceed the RCU tree capacity neither at compile-time nor in run-time. Therefore, if the condition is met in run- time then it indicates a serios problem elsewhere and should be handled with a panic.
--- kernel/rcu/tree.c | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-)
kernel/rcu/tree.c +17 -12
@@ -4107,6 +4107,19 @@ static void __init rcu_init_geometry(void) rcu_fanout_leaf, nr_cpu_ids);/* +* The boot-time rcu_fanout_leaf parameter is only permitted +* to increase the leaf-level fanout, not decrease it. Of course, +* the leaf-level fanout cannot exceed the number of bits in +* the rcu_node masks. Complain and fall back to the compile- +* time values if these limits are exceeded. +*/ +if (rcu_fanout_leaf <RCU_FANOUT_LEAF || + rcu_fanout_leaf >sizeof (unsigned long ) *8 ) { +WARN_ON (1 ); +return ; + } + +/* * Compute number of nodes that can be handled an rcu_node tree * with the given number of levels. Setting rcu_capacity[0] makes * some of the arithmetic easier.
@@ -4117,19 +4130,11 @@ static void __init rcu_init_geometry(void) rcu_capacity[i] = rcu_capacity[i -1 ] *RCU_FANOUT ;/* -* The boot-time rcu_fanout_leaf parameter is only permitted -* to increase the leaf-level fanout, not decrease it. Of course, -* the leaf-level fanout cannot exceed the number of bits in -* the rcu_node masks. Finally, the tree must be able to accommodate -* the configured number of CPUs. Complain and fall back to the -* compile-time values if these limits are exceeded. +* The tree must be able to accommodate the configured number of CPUs. +* If this limit is exceeded than we have a serious problem elsewhere. */ -if (rcu_fanout_leaf <RCU_FANOUT_LEAF || - rcu_fanout_leaf >sizeof (unsigned long ) *8 || - n > rcu_capacity[MAX_RCU_LVLS ]) { -WARN_ON (1 ); -return ; - } +if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );/* Calculate the number of rcu_nodes at each level of the tree. */ for (i =1 ; i <=MAX_RCU_LVLS ; i++)
Signature · 1 line
1.8.1.5
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );
How can this ever happen? We _know_ NR_CPUS at compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 7 lines · Peter Zijlstra
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );How can this ever happen? We _know_
NR_CPUSat compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.
You can make this happen by building with CONFIG_RCU_FANOUT=2 and CONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs. The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted for CONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this sort of thing for my rcutorture testing in order to test a four-level rcu_node tree with only 16 CPUs.
Thanx, Paul
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 9 lines · Paul E. McKenney
Quoted 7 lines · Peter Zijlstra
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );How can this ever happen? We _know_
NR_CPUSat compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.
Quoted 6 lines
You can make this happen by building with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs. The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted forCONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this sort of thing for my rcutorture testing in order to test a four-levelrcu_nodetree with only 16 CPUs.
How about we make the build fail if NR_CPUS exceeds that maximum fanout?
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 10 lines · Peter Zijlstra
Quoted 9 lines · Paul E. McKenney
Quoted 7 lines · Peter Zijlstra
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );How can this ever happen? We _know_
NR_CPUSat compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.
Quoted 8 lines
Quoted 6 lines
You can make this happen by building with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs. The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted forCONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this sort of thing for my rcutorture testing in order to test a four-levelrcu_nodetree with only 16 CPUs.How about we make the build fail if
NR_CPUSexceeds that maximum fanout?
Or better yet, auto-select these numbers based on NR_CPUS and remove the configs.
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 18 lines · Peter Zijlstra
Quoted 17 lines · Peter Zijlstra
Quoted 15 lines · Paul E. McKenney
Quoted 7 lines · Peter Zijlstra
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );How can this ever happen? We _know_
NR_CPUSat compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.You can make this happen by building with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs. The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted forCONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this sort of thing for my rcutorture testing in order to test a four-levelrcu_nodetree with only 16 CPUs.
Quoted 4 lines
Quoted 1 line
How about we make the build fail if
NR_CPUSexceeds that maximum fanout?Or better yet, auto-select these numbers based on
NR_CPUSand remove the configs.
The current strategy is to default CONFIG_RCU_FANOUT to 32 on 32-bit systems and to 64 on 64-bit systems, and to default CONFIG_RCU_FANOUT_LEAF to 16. This accommodates up to 4,194,304 CPUs, which should be enough for anyone (famous last words!). At boot time, RCU automatically shrinks its combining tree based on the value of nr_cpu_ids. So the overall effect is that very few people should need to mess with these RCU parameters.
The purpose of the CONFIG_RCU_FANOUT_LEAF=16 default is to keep lock contention down to a dull roar on systems that deliver the scheduling-clock interrupts simultaneously across all CPUs, and you should boot with skew_tick if you want to set CONFIG_RCU_FANOUT_LEAF larger.
Thanx, Paul
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
In reply to Peter ZijlstraQuoted 10 lines · Peter Zijlstra
Quoted 9 lines · Paul E. McKenney
Quoted 7 lines · Peter Zijlstra
kernel/rcu/tree.c static void __init rcu_init_geometry(void) · line 4137
Quoted 2 lines · Paul E. McKenney
kernel/rcu/tree.c +2
-0+if (n > rcu_capacity[MAX_RCU_LVLS ]) +panic ("rcu_init_geometry: rcu_capacity[] is too small" );How can this ever happen? We _know_
NR_CPUSat compile time, there's no way we can get more CPUs than that -- even if the hardware has more, we'll stop enumerating.
Quoted 8 lines
Quoted 6 lines
You can make this happen by building with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=2, then running on a system with more than 16 CPUs. The kernel boot parameter rcutree.rcu_fanout_leaf=2 can be substituted forCONFIG_RCU_FANOUT_LEAF=2, hence the need for a runtime test. I do this sort of thing for my rcutorture testing in order to test a four-levelrcu_nodetree with only 16 CPUs.How about we make the build fail if
NR_CPUSexceeds that maximum fanout?
Good point, and it already does, and I clearly was confused, apologies.
So the real way to make this happen is (for example) to build with CONFIG_RCU_FANOUT=2 and CONFIG_RCU_FANOUT_LEAF=16 (the default), which could accommodate up to 128 CPUs. Then boot with rcutree.rcu_fanout_leaf=2 on a system with more than 16 CPUs, with rcutree.rcu_fanout_leaf=3 on a system with more than 24 CPUs, and so on.
Of course, the truly macho way to get this error message is to build with CONFIG_RCU_FANOUT=64 and CONFIG_RCU_FANOUT_LEAF=64, then boot with rcutree.rcu_fanout_leaf=63 on a system with more than 16,515,072 CPUs. Of course, you get serious style points if the system manages to stay up for more than 24 hours without a hardware failure. ;-)
Thanx, Paul
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 7 lines · Paul E. McKenney
Good point, and it already does, and I clearly was confused, apologies.
So the real way to make this happen is (for example) to build with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=16(the default), which could accommodate up to 128 CPUs. Then boot with rcutree.rcu_fanout_leaf=2 on a system with more than 16 CPUs, with rcutree.rcu_fanout_leaf=3 on a system with more than 24 CPUs, and so on.
Ah, runtime overrides and operator error, but then we can WARN(), reset the arguments and try again, right? No need to panic the machine and fail to boot.
Quoted 5 lines
Of course, the truly macho way to get this error message is to build with
CONFIG_RCU_FANOUT=64andCONFIG_RCU_FANOUT_LEAF=64, then boot with rcutree.rcu_fanout_leaf=63 on a system with more than 16,515,072 CPUs. Of course, you get serious style points if the system manages to stay up for more than 24 hours without a hardware failure. ;-)
Yes, I'll go power up the nuclear reactor in the basement first :-)
Re: [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs
Quoted 10 lines · Peter Zijlstra
Quoted 7 lines · Paul E. McKenney
Good point, and it already does, and I clearly was confused, apologies.
So the real way to make this happen is (for example) to build with
CONFIG_RCU_FANOUT=2andCONFIG_RCU_FANOUT_LEAF=16(the default), which could accommodate up to 128 CPUs. Then boot with rcutree.rcu_fanout_leaf=2 on a system with more than 16 CPUs, with rcutree.rcu_fanout_leaf=3 on a system with more than 24 CPUs, and so on.
Quoted 3 lines
Ah, runtime overrides and operator error, but then we can
WARN(), reset the arguments and try again, right? No need to panic the machine and fail to boot.
Good point, like the patch below? Which also legitimizes my example after the fact, as it previously simply prohibited having rcutree.rcu_fanout_leaf less than CONFIG_RCU_FANOUT_LEAF. :-/
Quoted 7 lines
Quoted 5 lines
Of course, the truly macho way to get this error message is to build with
CONFIG_RCU_FANOUT=64andCONFIG_RCU_FANOUT_LEAF=64, then boot with rcutree.rcu_fanout_leaf=63 on a system with more than 16,515,072 CPUs. Of course, you get serious style points if the system manages to stay up for more than 24 hours without a hardware failure. ;-)Yes, I'll go power up the nuclear reactor in the basement first :-)
Only one? ;-)
Thanx, Paul
------------------------------------------------------------------------
rcu: Eliminate panic when silly boot-time fanout specified
This commit loosens rcutree.rcu_fanout_leaf range checks and replaces a panic() with a fallback to compile-time values. This fallback is accompanied by a WARN_ON(), and both occur when the rcutree.rcu_fanout_leaf value is too small to accommodate the number of CPUs. For example, given the current four-level limit for the rcu_node tree, a system with more than 16 CPUs built with CONFIG_FANOUT=2 must have rcutree.rcu_fanout_leaf larger than 2.
Documentation/kernel-parameters.txt +6 -3
@@ -3059,9 +3059,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. cache-to-cache transfer latencies. rcutree.rcu_fanout_leaf= [KNL] - Increase the number of CPUs assigned to each - leaf rcu_node structure. Useful for very large - systems. + Change the number of CPUs assigned to each + leaf rcu_node structure. Useful for very + large systems, which will choose the value 64, + and for NUMA systems with large remote-access + latencies, which will choose a value aligned + with the appropriate hardware boundaries. rcutree.jiffies_till_sched_qs= [KNL] Set required age in jiffies for a
kernel/rcu/tree.c +11 -9
@@ -4216,13 +4216,12 @@ static void __init rcu_init_geometry(void) rcu_fanout_leaf, nr_cpu_ids);/* -* The boot-time rcu_fanout_leaf parameter is only permitted -* to increase the leaf-level fanout, not decrease it. Of course, -* the leaf-level fanout cannot exceed the number of bits in -* the rcu_node masks. Complain and fall back to the compile- -* time values if these limits are exceeded. +* The boot-time rcu_fanout_leaf parameter must be at least two +* and cannot exceed the number of bits in the rcu_node masks. +* Complain and fall back to the compile-time values if this +* limit is exceeded. */ -if (rcu_fanout_leaf <RCU_FANOUT_LEAF || +if (rcu_fanout_leaf <2 || rcu_fanout_leaf >sizeof (unsigned long ) *8 ) { rcu_fanout_leaf =RCU_FANOUT_LEAF ;WARN_ON (1 );
@@ -4239,10 +4238,13 @@ static void __init rcu_init_geometry(void)/* * The tree must be able to accommodate the configured number of CPUs. -* If this limit is exceeded than we have a serious problem elsewhere. +* If this limit is exceeded, fall back to the compile-time values. */ -if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS -1 ]) -panic ("rcu_init_geometry: rcu_capacity[] is too small" ); +if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS -1 ]) { + rcu_fanout_leaf =RCU_FANOUT_LEAF ; +WARN_ON (1 ); +return ; + }/* Calculate the number of levels in the tree. */ for (i =0 ; nr_cpu_ids > rcu_capacity[i]; i++) {
PATCH 3/12 rcu: Remove superfluous local variable in rcu_init_geometry()
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Local variable 'n' mimics 'nr_cpu_ids' while the both are used within one function. There is no reason for 'n' to exist whatsoever.
--- kernel/rcu/tree.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
kernel/rcu/tree.c +7 -7
@@ -4083,7 +4083,6 @@ static void __init rcu_init_geometry(void)ulong d;int i;int j; -int n = nr_cpu_ids;int rcu_capacity[MAX_RCU_LVLS +1 ];/*
@@ -4133,15 +4132,16 @@ static void __init rcu_init_geometry(void)* The tree must be able to accommodate the configured number of CPUs. * If this limit is exceeded than we have a serious problem elsewhere. */ -if (n > rcu_capacity[MAX_RCU_LVLS ]) +if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS ])panic ("rcu_init_geometry: rcu_capacity[] is too small" );/* Calculate the number of rcu_nodes at each level of the tree. */ for (i =1 ; i <=MAX_RCU_LVLS ; i++) -if (n <= rcu_capacity[i]) { -for (j =0 ; j <= i; j++) - num_rcu_lvl[j] = -DIV_ROUND_UP (n, rcu_capacity[i - j]); +if (nr_cpu_ids <= rcu_capacity[i]) { +for (j =0 ; j <= i; j++) { +int cap = rcu_capacity[i - j]; + num_rcu_lvl[j] =DIV_ROUND_UP (nr_cpu_ids, cap); + } rcu_num_lvls = i;for (j = i +1 ; j <=MAX_RCU_LVLS ; j++) num_rcu_lvl[j] =0 ;
@@ -4152,7 +4152,7 @@ static void __init rcu_init_geometry(void) rcu_num_nodes =0 ;for (i =0 ; i <=MAX_RCU_LVLS ; i++) rcu_num_nodes += num_rcu_lvl[i]; - rcu_num_nodes -= n; + rcu_num_nodes -= nr_cpu_ids; }/*
Signature · 1 line
1.8.1.5
PATCH 4/12 rcu: Cleanup rcu_init_geometry() code and arithmetics
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
This update simplifies rcu_init_geometry() code flow and makes calculation of the total number of rcu_node structures more easy to read.
The update relies on the fact num_rcu_lvl[] is never accessed beyond rcu_num_lvls index by the rest of the code. Therefore, there is no need initialize the whole num_rcu_lvl[].
--- kernel/rcu/tree.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-)
kernel/rcu/tree.c +10 -14
@@ -4082,7 +4082,6 @@ static void __init rcu_init_geometry(void) {ulong d;int i; -int j;int rcu_capacity[MAX_RCU_LVLS +1 ];/*
@@ -4135,24 +4134,21 @@ static void __init rcu_init_geometry(void)if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS ])panic ("rcu_init_geometry: rcu_capacity[] is too small" ); +/* Calculate the number of levels in the tree. */ +for (i =1 ; nr_cpu_ids > rcu_capacity[i]; i++) { + } + rcu_num_lvls = i; +/* Calculate the number of rcu_nodes at each level of the tree. */ -for (i =1 ; i <=MAX_RCU_LVLS ; i++) -if (nr_cpu_ids <= rcu_capacity[i]) { -for (j =0 ; j <= i; j++) { -int cap = rcu_capacity[i - j]; - num_rcu_lvl[j] =DIV_ROUND_UP (nr_cpu_ids, cap); - } - rcu_num_lvls = i; -for (j = i +1 ; j <=MAX_RCU_LVLS ; j++) - num_rcu_lvl[j] =0 ; -break ; - } +for (i =0 ; i < rcu_num_lvls; i++) { +int cap = rcu_capacity[rcu_num_lvls - i]; + num_rcu_lvl[i] =DIV_ROUND_UP (nr_cpu_ids, cap); + }/* Calculate the total number of rcu_node structures. */ rcu_num_nodes =0 ; -for (i =0 ; i <=MAX_RCU_LVLS ; i++) +for (i =0 ; i < rcu_num_lvls; i++) rcu_num_nodes += num_rcu_lvl[i]; - rcu_num_nodes -= nr_cpu_ids; }/*
Signature · 1 line
1.8.1.5
PATCH 5/12 rcu: Simplify rcu_init_geometry() capacity arithmetics
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Current code suggests that introducing the extra level to rcu_capacity[] array makes some of the arithmetic easier. Well, in fact it appears rather confusing and unnecessary.
--- kernel/rcu/tree.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-)
kernel/rcu/tree.c +8 -10
@@ -4082,7 +4082,7 @@ static void __init rcu_init_geometry(void) {ulong d;int i; -int rcu_capacity[MAX_RCU_LVLS +1 ]; +int rcu_capacity[MAX_RCU_LVLS ];/* * Initialize any unspecified boot parameters.
@@ -4119,29 +4119,27 @@ static void __init rcu_init_geometry(void)/* * Compute number of nodes that can be handled an rcu_node tree -* with the given number of levels. Setting rcu_capacity[0] makes -* some of the arithmetic easier. +* with the given number of levels. */ - rcu_capacity[0 ] =1 ; - rcu_capacity[1 ] = rcu_fanout_leaf; -for (i =2 ; i <=MAX_RCU_LVLS ; i++) + rcu_capacity[0 ] = rcu_fanout_leaf; +for (i =1 ; i <MAX_RCU_LVLS ; i++) rcu_capacity[i] = rcu_capacity[i -1 ] *RCU_FANOUT ;/* * The tree must be able to accommodate the configured number of CPUs. * If this limit is exceeded than we have a serious problem elsewhere. */ -if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS ]) +if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS -1 ])panic ("rcu_init_geometry: rcu_capacity[] is too small" );/* Calculate the number of levels in the tree. */ -for (i =1 ; nr_cpu_ids > rcu_capacity[i]; i++) { +for (i =0 ; nr_cpu_ids > rcu_capacity[i]; i++) { } - rcu_num_lvls = i; + rcu_num_lvls = i +1 ;/* Calculate the number of rcu_nodes at each level of the tree. */ for (i =0 ; i < rcu_num_lvls; i++) { -int cap = rcu_capacity[rcu_num_lvls - i]; +int cap = rcu_capacity[(rcu_num_lvls -1 ) - i]; num_rcu_lvl[i] =DIV_ROUND_UP (nr_cpu_ids, cap); }
Signature · 1 line
1.8.1.5
PATCH 6/12 rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Variable rcu_num_lvls is limited by RCU_NUM_LVLS macro. In turn, rcu_state::levelcnt[] array is never accessed beyond rcu_num_lvls. Thus, rcu_state::levelcnt[] is safe to limit to RCU_NUM_LVLS items.
Since rcu_num_lvls could be changed during boot (as result of rcutree.rcu_fanout_leaf kernel parameter update) one might assume a new value could overflow the value of RCU_NUM_LVLS. However, that is not the case, since leaf-level fanout is only permitted to increase, resulting in rcu_num_lvls possibly to decrease.
--- kernel/rcu/tree.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/rcu/tree.h +1 -1
@@ -443,7 +443,7 @@ do { \struct rcu_state {struct rcu_node node[NUM_RCU_NODES ];/* Hierarchy. */ struct rcu_node *level[RCU_NUM_LVLS ];/* Hierarchy levels. */ -u32 levelcnt[MAX_RCU_LVLS +1 ];/* # nodes in each level. */ +u32 levelcnt[RCU_NUM_LVLS ];/* # nodes in each level. */ u8 levelspread[RCU_NUM_LVLS ];/* kids/node in each level. */ u8 flavor_mask;/* bit in flavor mask. */ struct rcu_data __percpu *rda;/* pointer of percu rcu_data. */
Signature · 1 line
1.8.1.5
PATCH 7/12 rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Number of items in rcu_capacity[] array is defined by macro MAX_RCU_LVLS. However, that array is never accessed beyond RCU_NUM_LVLS index. Therefore, we can limit the array to RCU_NUM_LVLS items and eliminate MAX_RCU_LVLS. As result, in most cases the memory is conserved.
--- kernel/rcu/tree.c | 12 ++++++------ kernel/rcu/tree.h | 2 -- 2 files changed, 6 insertions(+), 8 deletions(-)
kernel/rcu/tree.c +6 -6
@@ -3998,19 +3998,19 @@ static void __init rcu_init_one(struct rcu_state *rsp,"rcu_node_0" ,"rcu_node_1" ,"rcu_node_2" , - "rcu_node_3" }; /* Match MAX_RCU_LVLS */ + "rcu_node_3" };static const char *const fqs[] = {"rcu_node_fqs_0" ,"rcu_node_fqs_1" ,"rcu_node_fqs_2" , -"rcu_node_fqs_3" };/* Match MAX_RCU_LVLS */ +"rcu_node_fqs_3" };static u8 fl_mask =0x1 ;int cpustride =1 ;int i;int j;struct rcu_node *rnp; -BUILD_BUG_ON (MAX_RCU_LVLS >ARRAY_SIZE (buf));/* Fix buf[] init! */ +BUILD_BUG_ON (RCU_NUM_LVLS >ARRAY_SIZE (buf));/* Fix buf[] init! */ /* Silence gcc 4.8 false positive about array index out of range. */ if (rcu_num_lvls <=0 || rcu_num_lvls >RCU_NUM_LVLS )
@@ -4082,7 +4082,7 @@ static void __init rcu_init_geometry(void) {ulong d;int i; -int rcu_capacity[MAX_RCU_LVLS ]; +int rcu_capacity[RCU_NUM_LVLS ];/* * Initialize any unspecified boot parameters.
@@ -4122,14 +4122,14 @@ static void __init rcu_init_geometry(void)* with the given number of levels. */ rcu_capacity[0 ] = rcu_fanout_leaf; -for (i =1 ; i <MAX_RCU_LVLS ; i++) +for (i =1 ; i <RCU_NUM_LVLS ; i++) rcu_capacity[i] = rcu_capacity[i -1 ] *RCU_FANOUT ;/* * The tree must be able to accommodate the configured number of CPUs. * If this limit is exceeded than we have a serious problem elsewhere. */ -if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS -1 ]) +if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS -1 ])panic ("rcu_init_geometry: rcu_capacity[] is too small" );/* Calculate the number of levels in the tree. */
kernel/rcu/tree.h +0 -2
@@ -36,8 +36,6 @@* Of course, your mileage may vary. */ -#define MAX_RCU_LVLS 4 -#ifdef CONFIG_RCU_FANOUT #define RCU_FANOUT CONFIG_RCU_FANOUT#else /* #ifdef CONFIG_RCU_FANOUT */
Signature · 1 line
1.8.1.5
PATCH 8/12 rcu: Remove unnecessary fields from rcu_state structure
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Members rcu_state::levelcnt[] and rcu_state::levelspread[] are only used at init. There is no reason to keep them afterwards.
--- kernel/rcu/tree.c | 27 +++++++++++++++------------ kernel/rcu/tree.h | 2 -- 2 files changed, 15 insertions(+), 14 deletions(-)
kernel/rcu/tree.c +15 -12
@@ -3967,22 +3967,22 @@ void rcu_scheduler_starting(void)* Compute the per-level fanout, either using the exact fanout specified * or balancing the tree, depending on the rcu_fanout_exact boot parameter. */ -static void __init rcu_init_levelspread (struct rcu_state *rsp) +static void __init rcu_init_levelspread (int *levelspread,const int *levelcnt) {int i;if (rcu_fanout_exact) { - rsp->levelspread[rcu_num_lvls -1 ] = rcu_fanout_leaf; + levelspread[rcu_num_lvls -1 ] = rcu_fanout_leaf;for (i = rcu_num_lvls -2 ; i >=0 ; i--) - rsp->levelspread[i] =RCU_FANOUT ; + levelspread[i] =RCU_FANOUT ; }else {int ccur;int cprv; cprv = nr_cpu_ids;for (i = rcu_num_lvls -1 ; i >=0 ; i--) { - ccur = rsp->levelcnt[i]; - rsp->levelspread[i] = (cprv + ccur -1 ) / ccur; + ccur = levelcnt[i]; + levelspread[i] = (cprv + ccur -1 ) / ccur; cprv = ccur; } }
@@ -4005,6 +4005,9 @@ static void __init rcu_init_one(struct rcu_state *rsp,"rcu_node_fqs_2" , "rcu_node_fqs_3" };static u8 fl_mask =0x1 ; + +int levelcnt[RCU_NUM_LVLS ];/* # nodes in each level. */ +int levelspread[RCU_NUM_LVLS ];/* kids/node in each level. */ int cpustride =1 ;int i;int j;
@@ -4019,19 +4022,19 @@ static void __init rcu_init_one(struct rcu_state *rsp,/* Initialize the level-tracking arrays. */ for (i =0 ; i < rcu_num_lvls; i++) - rsp->levelcnt[i] = num_rcu_lvl[i]; + levelcnt[i] = num_rcu_lvl[i];for (i =1 ; i < rcu_num_lvls; i++) - rsp->level[i] = rsp->level[i -1 ] + rsp->levelcnt[i -1 ]; -rcu_init_levelspread (rsp); + rsp->level[i] = rsp->level[i -1 ] + levelcnt[i -1 ]; +rcu_init_levelspread (levelspread, levelcnt); rsp->flavor_mask = fl_mask; fl_mask <<=1 ;/* Initialize the elements themselves, starting from the leaves. */ for (i = rcu_num_lvls -1 ; i >=0 ; i--) { - cpustride *= rsp->levelspread[i]; + cpustride *= levelspread[i]; rnp = rsp->level[i]; -for (j =0 ; j < rsp->levelcnt[i]; j++, rnp++) { +for (j =0 ; j < levelcnt[i]; j++, rnp++) {raw_spin_lock_init (&rnp->lock);lockdep_set_class_and_name (&rnp->lock, &rcu_node_class[i], buf[i]);
@@ -4051,10 +4054,10 @@ static void __init rcu_init_one(struct rcu_state *rsp, rnp->grpmask =0 ; rnp->parent =NULL ; }else { - rnp->grpnum = j % rsp->levelspread[i -1 ]; + rnp->grpnum = j % levelspread[i -1 ]; rnp->grpmask =1UL << rnp->grpnum; rnp->parent = rsp->level[i -1 ] + - j / rsp->levelspread[i -1 ]; + j / levelspread[i -1 ]; } rnp->level = i;INIT_LIST_HEAD (&rnp->blkd_tasks);
kernel/rcu/tree.h +0 -2
@@ -441,8 +441,6 @@ do { \struct rcu_state {struct rcu_node node[NUM_RCU_NODES ];/* Hierarchy. */ struct rcu_node *level[RCU_NUM_LVLS ];/* Hierarchy levels. */ -u32 levelcnt[RCU_NUM_LVLS ];/* # nodes in each level. */ -u8 levelspread[RCU_NUM_LVLS ];/* kids/node in each level. */ u8 flavor_mask;/* bit in flavor mask. */ struct rcu_data __percpu *rda;/* pointer of percu rcu_data. */ void (*call)(struct rcu_head *head, /* call_rcu() flavor. */
Signature · 1 line
1.8.1.5
PATCH 9/12 rcu: Limit count of static data to the number of RCU levels
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Although a number of RCU levels may be less than the current maximum of four, some static data associated with each level are allocated for all four levels. As result, the extra data never get accessed and just wast memory. This update limits count of allocated items to the number of used RCU levels.
--- kernel/rcu/tree.c | 21 ++++----------------- kernel/rcu/tree.h | 12 ++++++++++++ 2 files changed, 16 insertions(+), 17 deletions(-)
kernel/rcu/tree.c +4 -17
@@ -124,13 +124,8 @@ module_param(rcu_fanout_exact, bool, 0444);static int rcu_fanout_leaf =RCU_FANOUT_LEAF ;module_param (rcu_fanout_leaf, int,0444 );int rcu_num_lvls__read_mostly =RCU_NUM_LVLS ; -static int num_rcu_lvl[] = {/* Number of rcu_nodes at specified level. */ -NUM_RCU_LVL_0 , -NUM_RCU_LVL_1 , -NUM_RCU_LVL_2 , -NUM_RCU_LVL_3 , -NUM_RCU_LVL_4 , -}; +/* Number of rcu_nodes at specified level. */ +static int num_rcu_lvl[] =NUM_RCU_LVL_INIT ;int rcu_num_nodes__read_mostly =NUM_RCU_NODES ;/* Total # rcu_nodes in use. */ /*
@@ -3994,16 +3989,8 @@ static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)static void __init rcu_init_one (struct rcu_state *rsp,struct rcu_data __percpu *rda) { -static const char *const buf[] = { -"rcu_node_0" , -"rcu_node_1" , -"rcu_node_2" , -"rcu_node_3" }; -static const char *const fqs[] = { -"rcu_node_fqs_0" , -"rcu_node_fqs_1" , -"rcu_node_fqs_2" , -"rcu_node_fqs_3" }; +static const char *const buf[] =RCU_NODE_NAME_INIT ; +static const char *const fqs[] =RCU_FQS_NAME_INIT ;static u8 fl_mask =0x1 ;int levelcnt[RCU_NUM_LVLS ];/* # nodes in each level. */
kernel/rcu/tree.h +12 -0
@@ -68,6 +68,9 @@# define NUM_RCU_LVL_2 0# define NUM_RCU_LVL_3 0# define NUM_RCU_LVL_4 0 +# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0 } +# define RCU_NODE_NAME_INIT { "rcu_node_0" } +# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" }#elif NR_CPUS <=RCU_FANOUT_2 # define RCU_NUM_LVLS 2# define NUM_RCU_LVL_0 1
@@ -75,6 +78,9 @@# define NUM_RCU_LVL_2 (NR_CPUS)# define NUM_RCU_LVL_3 0# define NUM_RCU_LVL_4 0 +# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1 } +# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" } +# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" }#elif NR_CPUS <=RCU_FANOUT_3 # define RCU_NUM_LVLS 3# define NUM_RCU_LVL_0 1
@@ -82,6 +88,9 @@# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)# define NUM_RCU_LVL_3 (NR_CPUS)# define NUM_RCU_LVL_4 0 +# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 } +# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" } +# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }#elif NR_CPUS <=RCU_FANOUT_4 # define RCU_NUM_LVLS 4# define NUM_RCU_LVL_0 1
@@ -89,6 +98,9 @@# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)# define NUM_RCU_LVL_4 (NR_CPUS) +# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 } +# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" } +# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }#else # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
Signature · 1 line
1.8.1.5
PATCH 10/12 rcu: Simplify arithmetic to calculate number of RCU nodes
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
This update makes arithmetic to calculate number of RCU nodes more straight and easy to read.
--- kernel/rcu/tree.h | 17 ++++------------- kernel/rcu/tree_plugin.h | 4 ++-- 2 files changed, 6 insertions(+), 15 deletions(-)
kernel/rcu/tree.h +4 -13
@@ -64,10 +64,7 @@#if NR_CPUS <=RCU_FANOUT_1 # define RCU_NUM_LVLS 1# define NUM_RCU_LVL_0 1 -# define NUM_RCU_LVL_1 (NR_CPUS) -# define NUM_RCU_LVL_2 0 -# define NUM_RCU_LVL_3 0 -# define NUM_RCU_LVL_4 0 +# define NUM_RCU_NODES NUM_RCU_LVL_0# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0 }# define RCU_NODE_NAME_INIT { "rcu_node_0" }# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0" }
@@ -75,9 +72,7 @@# define RCU_NUM_LVLS 2# define NUM_RCU_LVL_0 1# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) -# define NUM_RCU_LVL_2 (NR_CPUS) -# define NUM_RCU_LVL_3 0 -# define NUM_RCU_LVL_4 0 +# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1)# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1 }# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1" }# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1" }
@@ -86,8 +81,7 @@# define NUM_RCU_LVL_0 1# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) -# define NUM_RCU_LVL_3 (NR_CPUS) -# define NUM_RCU_LVL_4 0 +# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2)# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2 }# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2" }# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2" }
@@ -97,7 +91,7 @@# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1) -# define NUM_RCU_LVL_4 (NR_CPUS) +# define NUM_RCU_NODES (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)# define NUM_RCU_LVL_INIT { NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3 }# define RCU_NODE_NAME_INIT { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }# define RCU_FQS_NAME_INIT { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }
@@ -105,9 +99,6 @@# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"#endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */ -#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4) -#define NUM_RCU_NODES (RCU_SUM - NR_CPUS) -extern int rcu_num_lvls;extern int rcu_num_nodes;
kernel/rcu/tree_plugin.h +2 -2
@@ -84,8 +84,8 @@ static void __init rcu_bootup_announce_oddness(void)pr_info ("\tRCU torture testing starts during boot.\n" );if (IS_ENABLED (CONFIG_RCU_CPU_STALL_INFO ))pr_info ("\tAdditional per-CPU info printed with stalls.\n" ); -if (NUM_RCU_LVL_4 !=0 ) -pr_info ("\tFour-level hierarchy is enabled.\n" ); +if (RCU_NUM_LVLS >=4 ) +pr_info ("\tFour(or more)-level hierarchy is enabled.\n" );if (RCU_FANOUT_LEAF !=16 )pr_info ("\tBuild-time adjustment of leaf fanout to %d.\n" ,RCU_FANOUT_LEAF );
Signature · 1 line
1.8.1.5
PATCH 11/12 rcu: Shut up bogus gcc array bounds warning
In reply to Paul E. McKenneyFrom: Alexander Gordeev <[email protected]>
Because gcc does not realize a loop would not be entered ever (i.e. in case of rcu_num_lvls == 1):
for (i = 1; i < rcu_num_lvls; i++)
rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
some compiler (pre- 5.x?) versions give a bogus warning:
kernel/rcu/tree.c: In function ‘rcu_init_one.isra.55’:
kernel/rcu/tree.c:4108:13: warning: array subscript is above array bounds [-Warray-bounds]
rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
^Fix that warning by adding an extra item to rcu_state::level[] array. Once the bogus warning is fixed in gcc and kernel drops support of older versions, the dummy item may be removed from the array.
--- kernel/rcu/tree.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
kernel/rcu/tree.h +3 -1
@@ -443,7 +443,9 @@ do { \*/ struct rcu_state {struct rcu_node node[NUM_RCU_NODES ];/* Hierarchy. */ -struct rcu_node *level[RCU_NUM_LVLS ];/* Hierarchy levels. */ +struct rcu_node *level[RCU_NUM_LVLS +1 ]; +/* Hierarchy levels (+1 to */ +/* shut bogus gcc warning) */ u8 flavor_mask;/* bit in flavor mask. */ struct rcu_data __percpu *rda;/* pointer of percu rcu_data. */ void (*call)(struct rcu_head *head, /* call_rcu() flavor. */
Signature · 1 line
1.8.1.5
PATCH 12/12 rcu: Reset rcu_fanout_leaf if out of bounds
In reply to Paul E. McKenneyFrom: "Paul E. McKenney" <[email protected]>
Currently if the rcu_fanout_leaf boot parameter is out of bounds (that is, less than RCU_FANOUT_LEAF or greater than the number of bits in an unsigned long), a warning is issued and execution continues with the out-of-bounds value. This can result in all manner of failures, so this patch resets rcu_fanout_leaf to RCU_FANOUT_LEAF when an out-of-bounds condition is detected.
--- kernel/rcu/tree.c | 1 + 1 file changed, 1 insertion(+)
kernel/rcu/tree.c +1 -0
@@ -4103,6 +4103,7 @@ static void __init rcu_init_geometry(void)*/ if (rcu_fanout_leaf <RCU_FANOUT_LEAF || rcu_fanout_leaf >sizeof (unsigned long ) *8 ) { + rcu_fanout_leaf =RCU_FANOUT_LEAF ;WARN_ON (1 );return ; }
Signature · 1 line
1.8.1.5