Date: Thu, 25 Sep 2025 11:51:06 GMT From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: a15f2c5cc58f - main - proc: perform P_CONTROLT check on fork without SESS_LOCK Message-ID: <202509251151.58PBp6Qx006607@gitrepo.freebsd.org>
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The branch main has been updated by mjg: URL: https://cgit.FreeBSD.org/src/commit/?id=a15f2c5cc58f403407daf797a2e6963adffa6c2c commit a15f2c5cc58f403407daf797a2e6963adffa6c2c Author: Mateusz Guzik <mjg@FreeBSD.org> AuthorDate: 2025-09-25 11:50:01 +0000 Commit: Mateusz Guzik <mjg@FreeBSD.org> CommitDate: 2025-09-25 11:50:55 +0000 proc: perform P_CONTROLT check on fork without SESS_LOCK The flag is guarded by proc lock which is already held. After tracing poudriere for over 4 hours like so: dtrace -n 'fbt::do_fork:entry { @[curthread->td_proc->p_flag & 0x2] = count(); }': 2 15605151 0 20074116 Over 56% of cases did not have P_CONTROLT set and could have avoided the lock. This reduces hold time of the proctree lock. --- sys/kern/kern_fork.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c index 2ab9b363f8b5..7f6abae187b3 100644 --- a/sys/kern/kern_fork.c +++ b/sys/kern/kern_fork.c @@ -610,10 +610,12 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread * p2->p_flag |= p1->p_flag & P_SUGID; td2->td_pflags |= td->td_pflags & (TDP_ALTSTACK | TDP_SIGFASTBLOCK); td2->td_pflags2 |= td->td_pflags2 & TDP2_UEXTERR; - SESS_LOCK(p1->p_session); - if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) - p2->p_flag |= P_CONTROLT; - SESS_UNLOCK(p1->p_session); + if (p1->p_flag & P_CONTROLT) { + SESS_LOCK(p1->p_session); + if (p1->p_session->s_ttyvp != NULL) + p2->p_flag |= P_CONTROLT; + SESS_UNLOCK(p1->p_session); + } if (fr->fr_flags & RFPPWAIT) p2->p_flag |= P_PPWAIT;
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