Date: Fri, 7 Dec 2018 12:32:26 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r341685 - head/sys/kern Message-ID: <201812071232.wB7CWQOT053385@repo.freebsd.org>
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Author: mjg Date: Fri Dec 7 12:32:25 2018 New Revision: 341685 URL: https://svnweb.freebsd.org/changeset/base/341685 Log: proc: when exiting move to zombproc before taking proctree The kernel was already doing this prior to r329615. It was changed to reduce contention on allproc. However, introduction of pidhash locks and removal of proctree -> allproc ordering from fork thanks to bitmaps fixed things enough to make this change pessimal. waitpid takes proctree on each call and this change (now) causes avoidable stalls if allproc is held. Sponsored by: The FreeBSD Foundation Modified: head/sys/kern/kern_exit.c Modified: head/sys/kern/kern_exit.c ============================================================================== --- head/sys/kern/kern_exit.c Fri Dec 7 12:22:32 2018 (r341684) +++ head/sys/kern/kern_exit.c Fri Dec 7 12:32:25 2018 (r341685) @@ -448,7 +448,6 @@ exit1(struct thread *td, int rval, int signo) WITNESS_WARN(WARN_PANIC, NULL, "process (pid %d) exiting", p->p_pid); - sx_xlock(&proctree_lock); /* * Move proc from allproc queue to zombproc. */ @@ -458,6 +457,8 @@ exit1(struct thread *td, int rval, int signo) LIST_INSERT_HEAD(&zombproc, p, p_list); sx_xunlock(&zombproc_lock); sx_xunlock(&allproc_lock); + + sx_xlock(&proctree_lock); /* * Reparent all children processes:
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