Date: Sat, 8 Jul 2023 19:07:31 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 7a70f17ac4bd - main - killpg(): more carefully avoid LoR Message-ID: <202307081907.368J7VLL011285@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=7a70f17ac4bd64dc1a5020f963ba4380cf37b7e5 commit 7a70f17ac4bd64dc1a5020f963ba4380cf37b7e5 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2023-07-07 17:19:33 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2023-07-08 19:05:25 +0000 killpg(): more carefully avoid LoR otherwise we could end up with the livelock. When pg_killsx trylock failed, ensure that we do wait for lock availability before retry. Reported and tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 1 week --- sys/kern/kern_proc.c | 15 +++++++++++++-- sys/kern/kern_prot.c | 6 ++---- 2 files changed, 15 insertions(+), 6 deletions(-) diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c index 6d804d93eccc..b82dd07b17c1 100644 --- a/sys/kern/kern_proc.c +++ b/sys/kern/kern_proc.c @@ -587,8 +587,12 @@ enterpgrp(struct proc *p, pid_t pgid, struct pgrp *pgrp, struct session *sess) ("enterpgrp: session leader attempted setpgrp")); old_pgrp = p->p_pgrp; - if (!sx_try_xlock(&old_pgrp->pg_killsx)) + if (!sx_try_xlock(&old_pgrp->pg_killsx)) { + sx_xunlock(&proctree_lock); + sx_xlock(&old_pgrp->pg_killsx); + sx_xunlock(&old_pgrp->pg_killsx); return (ERESTART); + } MPASS(old_pgrp == p->p_pgrp); if (sess != NULL) { @@ -656,11 +660,18 @@ enterthispgrp(struct proc *p, struct pgrp *pgrp) ("%s: p %p belongs to pgrp %p", __func__, p, pgrp)); old_pgrp = p->p_pgrp; - if (!sx_try_xlock(&old_pgrp->pg_killsx)) + if (!sx_try_xlock(&old_pgrp->pg_killsx)) { + sx_xunlock(&proctree_lock); + sx_xlock(&old_pgrp->pg_killsx); + sx_xunlock(&old_pgrp->pg_killsx); return (ERESTART); + } MPASS(old_pgrp == p->p_pgrp); if (!sx_try_xlock(&pgrp->pg_killsx)) { sx_xunlock(&old_pgrp->pg_killsx); + sx_xunlock(&proctree_lock); + sx_xlock(&pgrp->pg_killsx); + sx_xunlock(&pgrp->pg_killsx); return (ERESTART); } diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c index 1fac6c496945..46d73a471291 100644 --- a/sys/kern/kern_prot.c +++ b/sys/kern/kern_prot.c @@ -347,10 +347,8 @@ again: error = EPERM; } else { error = enterpgrp(p, p->p_pid, newpgrp, newsess); - if (error == ERESTART) { - sx_xunlock(&proctree_lock); + if (error == ERESTART) goto again; - } MPASS(error == 0); td->td_retval[0] = p->p_pid; newpgrp = NULL; @@ -460,11 +458,11 @@ again: error = enterthispgrp(targp, pgrp); } done: - sx_xunlock(&proctree_lock); KASSERT(error == 0 || newpgrp != NULL, ("setpgid failed and newpgrp is NULL")); if (error == ERESTART) goto again; + sx_xunlock(&proctree_lock); uma_zfree(pgrp_zone, newpgrp); return (error); }
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