Date: Sat, 24 Sep 2022 00:16:29 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: c2d27b0ec700 - main - sched_4bsd: Fix a racy thread state modification Message-ID: <202209240016.28O0GTSx031408@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=c2d27b0ec7000d28b4f31148005ccfe371f47db3 commit c2d27b0ec7000d28b4f31148005ccfe371f47db3 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2022-09-23 23:41:30 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-09-24 00:09:06 +0000 sched_4bsd: Fix a racy thread state modification When a thread switching off-CPU is migrating to a remote CPU, sched_switch() may trigger a rescheduling of the thread currently running on that CPU. When doing so, it must ensure that that thread is locked before modifying thread state. If the thread's lock is not the scheduler lock, then the thread is in the process of switching off-CPU and no extra effort is needed, and the initiator does not hold the thread's lock and thus should not modify any thread state. Reported and tested by: Steve Kargl MFC after: 1 week --- sys/kern/sched_4bsd.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c index 9d48aa746f6d..8bd697a67e7e 100644 --- a/sys/kern/sched_4bsd.c +++ b/sys/kern/sched_4bsd.c @@ -1282,9 +1282,10 @@ kick_other_cpu(int pri, int cpuid) } #endif /* defined(IPI_PREEMPTION) && defined(PREEMPTION) */ - ast_sched_locked(pcpu->pc_curthread, TDA_SCHED); - ipi_cpu(cpuid, IPI_AST); - return; + if (pcpu->pc_curthread->td_lock == &sched_lock) { + ast_sched_locked(pcpu->pc_curthread, TDA_SCHED); + ipi_cpu(cpuid, IPI_AST); + } } #endif /* SMP */
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