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Wed, 15 Oct 2025 06:08:51 GMT (envelope-from git) Date: Wed, 15 Oct 2025 06:08:51 GMT Message-Id: <202510150608.59F68pAb023185@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Colin Percival Subject: git: 9bea2657c453 - releng/15.0 - vfs offset: fix assertion failure in face of racing ffofset and setfl locking List-Id: Commits to the stable branches of the FreeBSD src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-branches List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-branches@freebsd.org Sender: owner-dev-commits-src-branches@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: cperciva X-Git-Repository: src X-Git-Refname: refs/heads/releng/15.0 X-Git-Reftype: branch X-Git-Commit: 9bea2657c4538f234709a97010f05e2b776c87a6 Auto-Submitted: auto-generated The branch releng/15.0 has been updated by cperciva: URL: https://cgit.FreeBSD.org/src/commit/?id=9bea2657c4538f234709a97010f05e2b776c87a6 commit 9bea2657c4538f234709a97010f05e2b776c87a6 Author: Mateusz Guzik AuthorDate: 2025-10-05 17:03:54 +0000 Commit: Colin Percival CommitDate: 2025-10-15 06:08:01 +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. Approved by: re (cperciva) Reviewed by: kib, markj Sponsored by: Rubicon Communications, LLC ("Netgate") Differential Revision: https://reviews.freebsd.org/D52915 (cherry picked from commit f43e19db6cea0a7dd7bf51f3fe2227d466ea5a80) --- 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);