The following commit has been merged into the locking/core branch of tip:
Commit-ID: 63a48181fbcddefe5fb4c6618938bb64c543945b
Gitweb: https://git.kernel.org/tip/63a48181fbcddefe5fb4c6618938bb64c543945b
Author: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
AuthorDate: Tue, 03 Dec 2024 11:35:58 -05:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 05 Dec 2024 14:25:28 +01:00
smp/scf: Evaluate local cond_func() before IPI side-effects
In smp_call_function_many_cond(), the local cond_func() is evaluated
after triggering the remote CPU IPIs.
If cond_func() depends on loading shared state updated by other CPU's
IPI handlers func(), then triggering execution of remote CPUs IPI before
evaluating cond_func() may have unexpected consequences.
One example scenario is evaluating a jiffies delay in cond_func(), which
is updated by func() in the IPI handlers. This situation can prevent
execution of periodic cleanup code on the local CPU.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241203163558.3455535-1-mathieu.desnoyers@xxxxxxxxxxxx
---
kernel/smp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/smp.c b/kernel/smp.c
index 27dc31a..f104c8e 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -815,7 +815,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
WARN_ON_ONCE(!in_task());
/* Check if we need local execution. */
- if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask))
+ if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask) &&
+ (!cond_func || cond_func(this_cpu, info)))
run_local = true;
/* Check if we need remote execution, i.e., any CPU excluding this one. */
@@ -868,7 +869,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
send_call_function_ipi_mask(cfd->cpumask_ipi);
}
- if (run_local && (!cond_func || cond_func(this_cpu, info))) {
+ if (run_local) {
unsigned long flags;
local_irq_save(flags);
|