tick/rcu: fix report_idle_softirq
PATCH 1/1 tick/rcu: fix report_idle_softirq
From: Wen Yang <[email protected]>
In commit 0345691b24c0 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the new function report_idle_softirq() was created by breaking code out of the existing can_stop_idle_tick() for kernels v5.18 and newer.
In doing so, the code essentially went from this form:
if (A) {
static int ratelimit;
if (ratelimit < 10 && !C && A&D) {
pr_warn("NOHZ tick-stop error: ...");
ratelimit++;
}
return false;
}to a new function:
static bool report_idle_softirq(void)
{
static int ratelimit;
if (likely(!A))
return false;
if (ratelimit < 10)
return false;
...
pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",
pending);
ratelimit++;
return true;
}commit a7e282c77785 ("tick/rcu: Fix bogus ratelimit condition") realized the ratelimit was essentially set to zero instead of ten, and hence *no* softirq pending messages would ever be issued, but fix it as:
- if (ratelimit < 10)
+ if (ratelimit >= 10)
return false;
However, this fix introduces another issue:
When ratelimit is greater than 10, even if A is true, it will directly return false. While ratelimit in the original code is only used to control printing and will not affect the return value.
This patch fixes the above issues.
--- kernel/time/tick-sched.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
kernel/time/tick-sched.c +5 -6
@@ -1174,16 +1174,15 @@ static bool report_idle_softirq(void)return false; } -if (ratelimit >=10 ) -return false; -/* On RT, softirq handling may be waiting on some lock */ if (local_bh_blocked ())return false; -pr_warn ("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n" , - pending); - ratelimit++; +if (ratelimit <10 ) { +pr_warn ("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n" , + pending); + ratelimit++; + }return true; }
Signature · 1 line
2.25.1
[tip: timers/urgent] tick/sched: Fix bogus condition in report_idle_softirq()
The following commit has been merged into the timers/urgent branch of tip:
The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: 807e0d187da4c0b22036b5e34000f7a8c52f6e50 Gitweb: https://git.kernel.org/tip/807e0d187da4c0b22036b5e34000f7a8c52f6e50 Author: Wen Yang <[email protected]> AuthorDate: Thu, 20 Nov 2025 01:45:25 +08:00 Committer: Thomas Gleixner <[email protected]> CommitterDate: Wed, 19 Nov 2025 19:30:45 +01:00
tick/sched: Fix bogus condition in report_idle_softirq()
In commit 0345691b24c0 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the new function report_idle_softirq() was created by breaking code out of the existing can_stop_idle_tick() for kernels v5.18 and newer.
In doing so, the code essentially went from this form:
if (A) {
static int ratelimit;
if (ratelimit < 10 && !C && A&D) {
pr_warn("NOHZ tick-stop error: ...");
ratelimit++;
}
return false;
}to a new function:
static bool report_idle_softirq(void)
{
static int ratelimit;
if (likely(!A))
return false;
if (ratelimit < 10)
return false;
...
pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",
pending);
ratelimit++;
return true;
}commit a7e282c77785 ("tick/rcu: Fix bogus ratelimit condition") realized ratelimit was essentially set to zero instead of ten, and hence *no* softirq pending messages would ever be issued, but "fixed" it as:
- if (ratelimit < 10)
+ if (ratelimit >= 10)
return false;
However, this fix introduced another issue:
When ratelimit is greater than or equal 10, even if A is true, it will directly return false. While ratelimit in the original code was only used to control printing and will not affect the return value.
Restore the original logic and restrict ratelimit to control the printk and not the return value.
--- kernel/time/tick-sched.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
kernel/time/tick-sched.c +5 -6
@@ -1152,16 +1152,15 @@ static bool report_idle_softirq(void)return false; } -if (ratelimit >=10 ) -return false; -/* On RT, softirq handling may be waiting on some lock */ if (local_bh_blocked ())return false; -pr_warn ("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n" , - pending); - ratelimit++; +if (ratelimit <10 ) { +pr_warn ("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n" , + pending); + ratelimit++; + }return true; }