From 63a48181fbcddefe5fb4c6618938bb64c543945b Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 3 Dec 2024 11:35:58 -0500 Subject: [PATCH] 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 Signed-off-by: Ingo Molnar Reviewed-by: Rik van Riel Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lore.kernel.org/r/20241203163558.3455535-1-mathieu.desnoyers@efficios.com --- kernel/smp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 27dc31a146a35..f104c8e83fc4c 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);