printk/sched: Introduce special printk_sched() for those awkward moments
Commit-ID: 3ccf3e8306156a28213adc720aba807e9a901ad5 Gitweb: http://git.kernel.org/tip/3ccf3e8306156a28213adc720aba807e9a901ad5 Author: Peter Zijlstra <[email protected]> AuthorDate: Mon, 27 Feb 2012 10:47:00 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Mon, 12 Mar 2012 20:43:16 +0100
printk/sched: Introduce special printk_sched() for those awkward moments
There's a few awkward printk()s inside of scheduler guts that people prefer to keep but really are rather deadlock prone. Fudge around it by storing the text in a per-cpu buffer and poll it using the existing printk_tick() handler.
This will drop output when its more frequent than once a tick, however only the affinity thing could possible go that fast and for that just one should suffice to notify the admin he's done something silly..
Signed-off-by Peter Zijlstra <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Andrew Morton <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
--- include/linux/printk.h | 10 ++++++++++ kernel/printk.c | 40 +++++++++++++++++++++++++++++++++++++--- kernel/sched/core.c | 2 +- kernel/sched/rt.c | 8 +++++++- 4 files changed, 55 insertions(+), 5 deletions(-)
include/linux/printk.h +10 -0
@@ -101,6 +101,11 @@ asmlinkage __printf(1, 2) __coldint printk (const char *fmt, ...);/* +* Special printk facility for scheduler use only, _DO_NOT_USE_ ! +*/ +__printf(1, 2) __cold int printk_sched(const char *fmt, ...); + +/* * Please don't use printk_ratelimit(), because it shares ratelimiting state * with all other unrelated printk_ratelimit() callsites. Instead use * printk_ratelimited() or plain old __ratelimit().
@@ -127,6 +132,11 @@ int printk(const char *s, ...) {return 0 ; } +static inline __printf(1, 2) __cold +int printk_sched(const char *s, ...) +{ +return 0 ; +}static inline int printk_ratelimit (void ) {return 0 ;
kernel/printk.c +37 -3
@@ -1208,13 +1208,47 @@ int is_console_locked(void)return console_locked; } +/* +* Delayed printk facility, for scheduler-internal messages: +*/ +#define PRINTK_BUF_SIZE 512 + +#define PRINTK_PENDING_WAKEUP 0x01 +#define PRINTK_PENDING_SCHED 0x02 + static DEFINE_PER_CPU(int, printk_pending); +static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf); + +int printk_sched (const char *fmt, ...) +{ +unsigned long flags; +va_list args; +char *buf; +int r; + +local_irq_save (flags); + buf =__get_cpu_var (printk_sched_buf); + +va_start (args, fmt); + r =vsnprintf (buf,PRINTK_BUF_SIZE , fmt, args); +va_end (args); + +__this_cpu_or (printk_pending,PRINTK_PENDING_SCHED ); +local_irq_restore (flags); + +return r; +}void printk_tick (void ) {if (__this_cpu_read (printk_pending)) { -__this_cpu_write (printk_pending,0 ); -wake_up_interruptible (&log_wait); +int pending =__this_cpu_xchg (printk_pending,0 ); +if (pending &PRINTK_PENDING_SCHED ) { +char *buf =__get_cpu_var (printk_sched_buf); +printk (KERN_WARNING "[sched_delayed] %s" , buf); + } +if (pending &PRINTK_PENDING_WAKEUP ) +wake_up_interruptible (&log_wait); } }
@@ -1228,7 +1262,7 @@ int printk_needs_cpu(int cpu)void wake_up_klogd (void ) {if (waitqueue_active (&log_wait)) -this_cpu_write (printk_pending,1 ); +this_cpu_or (printk_pending,PRINTK_PENDING_WAKEUP ); }/**
kernel/sched/core.c +1 -1
@@ -1284,7 +1284,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)* leave kernel. */ if (p->mm &&printk_ratelimit ()) { -printk (KERN_INFO "process %d (%s) no longer affine to cpu%d\n" , +printk_sched ("process %d (%s) no longer affine to cpu%d\n" ,task_pid_nr (p), p->comm, cpu); }
kernel/sched/rt.c +7 -1
@@ -864,8 +864,14 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)* but accrue some time due to boosting. */ if (likely (rt_b->rt_runtime)) { +static bool once = false; + rt_rq->rt_throttled =1 ; -printk_once (KERN_WARNING "sched: RT throttling activated\n" ); + +if (!once) { + once = true; +printk_sched ("sched: RT throttling activated\n" ); + } }else {/* * In case we did anyway, make it go away,