Date: Sat, 4 Oct 2025 09:10:08 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 7b980bf5e526 - stable/14 - kern/vfs_vnops.c: generalize the lock primitive for file foffset Message-ID: <202510040910.5949A80e098791@gitrepo.freebsd.org>
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The branch stable/14 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=7b980bf5e5262332c8f5679ad4dd7b17fd5db8a9 commit 7b980bf5e5262332c8f5679ad4dd7b17fd5db8a9 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2025-09-10 16:35:01 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2025-10-04 09:09:45 +0000 kern/vfs_vnops.c: generalize the lock primitive for file foffset (cherry picked from commit 94a0f9f63e164e4f3791bc7d105d6f267b4d47bc) --- sys/kern/vfs_vnops.c | 148 +++++++++++++++++++++++++++++++-------------------- sys/sys/file.h | 6 +-- 2 files changed, 94 insertions(+), 60 deletions(-) diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index 79fee79295fb..5b25e2680ee4 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -759,58 +759,82 @@ vn_rdwr_inchunks(enum uio_rw rw, struct vnode *vp, void *base, size_t len, } #if OFF_MAX <= LONG_MAX -off_t -foffset_lock(struct file *fp, int flags) +static void +file_v_lock(struct file *fp, short lock_bit, short lock_wait_bit) { - volatile short *flagsp; - off_t res; + short *flagsp; short state; - KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed")); - - if ((flags & FOF_NOLOCK) != 0) - return (atomic_load_long(&fp->f_offset)); - - /* - * According to McKusick the vn lock was protecting f_offset here. - * It is now protected by the FOFFSET_LOCKED flag. - */ - flagsp = &fp->f_vnread_flags; - if (atomic_cmpset_acq_16(flagsp, 0, FOFFSET_LOCKED)) - return (atomic_load_long(&fp->f_offset)); + flagsp = &fp->f_vflags; + state = atomic_load_16(flagsp); + if ((state & lock_bit) == 0 && + atomic_cmpset_acq_16(flagsp, state, state | lock_bit)) + return; - sleepq_lock(&fp->f_vnread_flags); + sleepq_lock(flagsp); state = atomic_load_16(flagsp); for (;;) { - if ((state & FOFFSET_LOCKED) == 0) { + if ((state & lock_bit) == 0) { if (!atomic_fcmpset_acq_16(flagsp, &state, - FOFFSET_LOCKED)) + state | lock_bit)) continue; break; } - if ((state & FOFFSET_LOCK_WAITING) == 0) { + if ((state & lock_wait_bit) == 0) { if (!atomic_fcmpset_acq_16(flagsp, &state, - state | FOFFSET_LOCK_WAITING)) + state | lock_wait_bit)) continue; } DROP_GIANT(); - sleepq_add(&fp->f_vnread_flags, NULL, "vofflock", 0, 0); - sleepq_wait(&fp->f_vnread_flags, PRI_MAX_KERN); + sleepq_add(flagsp, NULL, "vofflock", 0, 0); + sleepq_wait(flagsp, PRI_MAX_KERN); PICKUP_GIANT(); - sleepq_lock(&fp->f_vnread_flags); + sleepq_lock(flagsp); state = atomic_load_16(flagsp); } - res = atomic_load_long(&fp->f_offset); - sleepq_release(&fp->f_vnread_flags); - return (res); + sleepq_release(flagsp); } -void -foffset_unlock(struct file *fp, off_t val, int flags) +static void +file_v_unlock(struct file *fp, short lock_bit, short lock_wait_bit) { - volatile short *flagsp; + short *flagsp; short state; + 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; + + sleepq_lock(flagsp); + MPASS((*flagsp & lock_bit) != 0); + MPASS((*flagsp & lock_wait_bit) != 0); + atomic_clear_16(flagsp, lock_bit | lock_wait_bit); + sleepq_broadcast(flagsp, SLEEPQ_SLEEP, 0, 0); + sleepq_release(flagsp); +} + +off_t +foffset_lock(struct file *fp, int flags) +{ + KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed")); + + if ((flags & FOF_NOLOCK) == 0) { + file_v_lock(fp, FILE_V_FOFFSET_LOCKED, + FILE_V_FOFFSET_LOCK_WAITING); + } + + /* + * According to McKusick the vn lock was protecting f_offset here. + * It is now protected by the FOFFSET_LOCKED flag. + */ + return (atomic_load_long(&fp->f_offset)); +} + +void +foffset_unlock(struct file *fp, off_t val, int flags) +{ KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed")); if ((flags & FOF_NOUPDATE) == 0) @@ -820,21 +844,10 @@ foffset_unlock(struct file *fp, off_t val, int flags) if ((flags & FOF_NEXTOFF_W) != 0) fp->f_nextoff[UIO_WRITE] = val; - if ((flags & FOF_NOLOCK) != 0) - return; - - flagsp = &fp->f_vnread_flags; - state = atomic_load_16(flagsp); - if ((state & FOFFSET_LOCK_WAITING) == 0 && - atomic_cmpset_rel_16(flagsp, state, 0)) - return; - - sleepq_lock(&fp->f_vnread_flags); - MPASS((fp->f_vnread_flags & FOFFSET_LOCKED) != 0); - MPASS((fp->f_vnread_flags & FOFFSET_LOCK_WAITING) != 0); - fp->f_vnread_flags = 0; - sleepq_broadcast(&fp->f_vnread_flags, SLEEPQ_SLEEP, 0, 0); - sleepq_release(&fp->f_vnread_flags); + if ((flags & FOF_NOLOCK) == 0) { + file_v_unlock(fp, FILE_V_FOFFSET_LOCKED, + FILE_V_FOFFSET_LOCK_WAITING); + } } static off_t @@ -843,7 +856,35 @@ foffset_read(struct file *fp) return (atomic_load_long(&fp->f_offset)); } -#else + +#else /* OFF_MAX <= LONG_MAX */ + +static void +file_v_lock_mtxp(struct file *fp, struct mtx *mtxp, short lock_bit, + short lock_wait_bit) +{ + mtx_assert(mtxp, MA_OWNED); + + while ((fp->f_vflags & lock_bit) != 0) { + fp->f_vflags |= lock_wait_bit; + msleep(&fp->f_vflags, mtxp, PRI_MAX_KERN, + "vofflock", 0); + } + fp->f_vflags |= lock_bit; +} + +static void +file_v_unlock_mtxp(struct file *fp, struct mtx *mtxp, short lock_bit, + short lock_wait_bit) +{ + mtx_assert(mtxp, MA_OWNED); + + KASSERT((fp->f_vflags & lock_bit) != 0, ("Lost lock_bit")); + if ((fp->f_vflags & lock_wait_bit) != 0) + wakeup(&fp->f_vflags); + fp->f_vflags &= ~(lock_bit | lock_wait_bit); +} + off_t foffset_lock(struct file *fp, int flags) { @@ -855,12 +896,8 @@ foffset_lock(struct file *fp, int flags) mtxp = mtx_pool_find(mtxpool_sleep, fp); mtx_lock(mtxp); if ((flags & FOF_NOLOCK) == 0) { - while (fp->f_vnread_flags & FOFFSET_LOCKED) { - fp->f_vnread_flags |= FOFFSET_LOCK_WAITING; - msleep(&fp->f_vnread_flags, mtxp, PRI_MAX_KERN, - "vofflock", 0); - } - fp->f_vnread_flags |= FOFFSET_LOCKED; + file_v_lock_mtxp(fp, mtxp, FILE_V_FOFFSET_LOCKED, + FILE_V_FOFFSET_LOCK_WAITING); } res = fp->f_offset; mtx_unlock(mtxp); @@ -883,11 +920,8 @@ foffset_unlock(struct file *fp, off_t val, int flags) if ((flags & FOF_NEXTOFF_W) != 0) fp->f_nextoff[UIO_WRITE] = val; if ((flags & FOF_NOLOCK) == 0) { - KASSERT((fp->f_vnread_flags & FOFFSET_LOCKED) != 0, - ("Lost FOFFSET_LOCKED")); - if (fp->f_vnread_flags & FOFFSET_LOCK_WAITING) - wakeup(&fp->f_vnread_flags); - fp->f_vnread_flags = 0; + file_v_unlock_mtxp(fp, mtxp, FILE_V_FOFFSET_LOCKED, + FILE_V_FOFFSET_LOCK_WAITING); } mtx_unlock(mtxp); } diff --git a/sys/sys/file.h b/sys/sys/file.h index 7d1a191b4374..349605939d30 100644 --- a/sys/sys/file.h +++ b/sys/sys/file.h @@ -194,7 +194,7 @@ struct file { struct vnode *f_vnode; /* NULL or applicable vnode */ struct ucred *f_cred; /* associated credentials. */ short f_type; /* descriptor type */ - short f_vnread_flags; /* (f) Sleep lock for f_offset */ + short f_vflags; /* (f) Sleep lock flags for members */ /* * DTYPE_VNODE specific fields. */ @@ -217,8 +217,8 @@ struct file { #define f_cdevpriv f_vnun.fvn_cdevpriv #define f_advice f_vnun.fvn_advice -#define FOFFSET_LOCKED 0x1 -#define FOFFSET_LOCK_WAITING 0x2 +#define FILE_V_FOFFSET_LOCKED 0x0001 +#define FILE_V_FOFFSET_LOCK_WAITING 0x0002 #endif /* __BSD_VISIBLE */ #endif /* _KERNEL || _WANT_FILE */
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