Commit 63a48181 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Ingo Molnar
Browse files

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: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarRik 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
parent d387ceb1

kernel/smp.c

+3 −2
Original line number Diff line number Diff line
@@ -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);