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smp/scf: Evaluate local cond_func() before IPI side-effects

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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@efficios.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20241203163558.3455535-1-mathieu.desnoyers@efficios.com
This commit is contained in:
Mathieu Desnoyers 2024-12-03 11:35:58 -05:00 committed by Ingo Molnar
parent d387ceb171
commit 63a48181fb
1 changed files with 3 additions and 2 deletions
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5
kernel/smp.c
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@ -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);