Date: Wed, 15 Oct 2025 02:12:18 GMT From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: f43e19db6cea - stable/15 - vfs offset: fix assertion failure in face of racing ffofset and setfl locking Message-ID: <202510150212.59F2CIOG083490@gitrepo.freebsd.org>
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The branch stable/15 has been updated by mjg: URL: https://cgit.FreeBSD.org/src/commit/?id=f43e19db6cea0a7dd7bf51f3fe2227d466ea5a80 commit f43e19db6cea0a7dd7bf51f3fe2227d466ea5a80 Author: Mateusz Guzik <mjg@FreeBSD.org> AuthorDate: 2025-10-05 17:03:54 +0000 Commit: Mateusz Guzik <mjg@FreeBSD.org> CommitDate: 2025-10-15 02:12:05 +0000 vfs offset: fix assertion failure in face of racing ffofset and setfl locking Both use the same 16 bit var to store their locked and waiters bits, then this in file_v_unlock: state = atomic_load_16(flagsp); if ((state & lock_wait_bit) == 0 && atomic_cmpset_rel_16(flagsp, state, state & ~lock_bit)) return; can fail if for example foffset is being unlocked while setfl is getting locked. Afterwards the code assumes there are blocked waiters on foffset. Reviewed by: kib, markj Sponsored by: Rubicon Communications, LLC ("Netgate") Differential Revision: https://reviews.freebsd.org/D52915 --- sys/kern/vfs_vnops.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index f81c2033d95e..e27692ccb1a3 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -806,9 +806,12 @@ file_v_lock(struct file *fp, short lock_bit, short lock_wait_bit) flagsp = &fp->f_vflags; state = atomic_load_16(flagsp); - if ((state & lock_bit) == 0 && - atomic_cmpset_acq_16(flagsp, state, state | lock_bit)) - return; + for (;;) { + if ((state & lock_bit) != 0) + break; + if (atomic_fcmpset_acq_16(flagsp, &state, state | lock_bit)) + return; + } sleepq_lock(flagsp); state = atomic_load_16(flagsp); @@ -842,9 +845,12 @@ file_v_unlock(struct file *fp, short lock_bit, short lock_wait_bit) flagsp = &fp->f_vflags; state = atomic_load_16(flagsp); - if ((state & lock_wait_bit) == 0 && - atomic_cmpset_rel_16(flagsp, state, state & ~lock_bit)) - return; + for (;;) { + if ((state & lock_wait_bit) != 0) + break; + if (atomic_fcmpset_rel_16(flagsp, &state, state & ~lock_bit)) + return; + } sleepq_lock(flagsp); MPASS((*flagsp & lock_bit) != 0);
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