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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