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author | kib <kib@FreeBSD.org> | 2012-12-28 23:08:30 +0000 |
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committer | kib <kib@FreeBSD.org> | 2012-12-28 23:08:30 +0000 |
commit | 4247222fcc643b60a3b7a9f859bc22994ca75f4b (patch) | |
tree | 17461ae8de8771b3b7726b88cdeb957aaf3e054e /sys/kern/vfs_vnops.c | |
parent | bd8e345ca3212f607bc453c1c860e364601c1522 (diff) | |
download | FreeBSD-src-4247222fcc643b60a3b7a9f859bc22994ca75f4b.zip FreeBSD-src-4247222fcc643b60a3b7a9f859bc22994ca75f4b.tar.gz |
Make it possible to atomically resume writes on the mount and account
the write start, by adding a variation of the vfs_write_resume(9)
which accepts flags.
Use the new function to prevent a deadlock between parallel suspension
and snapshotting a UFS mount. The ffs_snapshot() code performed
vfs_write_resume() followed by vn_start_write() while owning the
snaplock. If the suspension intervene between resume and
vn_start_write(), the deadlock occured after the suspending thread
tried to lock the snaplock, most typically during the write in the
ffs_copyonwrite().
Reported and tested by: Andreas Longwitz <longwitz@incore.de>
Reviewed by: mckusick
MFC after: 2 weeks
X-MFC-note: make the vfs_write_resume(9) function a macro after the MFC,
in HEAD
Diffstat (limited to 'sys/kern/vfs_vnops.c')
-rw-r--r-- | sys/kern/vfs_vnops.c | 79 |
1 files changed, 52 insertions, 27 deletions
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index 3f65b05..cf49ecb 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -1434,6 +1434,40 @@ vn_closefile(fp, td) * proceed. If a suspend request is in progress, we wait until the * suspension is over, and then proceed. */ +static int +vn_start_write_locked(struct mount *mp, int flags) +{ + int error; + + mtx_assert(MNT_MTX(mp), MA_OWNED); + error = 0; + + /* + * Check on status of suspension. + */ + if ((curthread->td_pflags & TDP_IGNSUSP) == 0 || + mp->mnt_susp_owner != curthread) { + while ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) { + if (flags & V_NOWAIT) { + error = EWOULDBLOCK; + goto unlock; + } + error = msleep(&mp->mnt_flag, MNT_MTX(mp), + (PUSER - 1) | (flags & PCATCH), "suspfs", 0); + if (error) + goto unlock; + } + } + if (flags & V_XSLEEP) + goto unlock; + mp->mnt_writeopcount++; +unlock: + if (error != 0 || (flags & V_XSLEEP) != 0) + MNT_REL(mp); + MNT_IUNLOCK(mp); + return (error); +} + int vn_start_write(vp, mpp, flags) struct vnode *vp; @@ -1470,30 +1504,7 @@ vn_start_write(vp, mpp, flags) if (vp == NULL) MNT_REF(mp); - /* - * Check on status of suspension. - */ - if ((curthread->td_pflags & TDP_IGNSUSP) == 0 || - mp->mnt_susp_owner != curthread) { - while ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) { - if (flags & V_NOWAIT) { - error = EWOULDBLOCK; - goto unlock; - } - error = msleep(&mp->mnt_flag, MNT_MTX(mp), - (PUSER - 1) | (flags & PCATCH), "suspfs", 0); - if (error) - goto unlock; - } - } - if (flags & V_XSLEEP) - goto unlock; - mp->mnt_writeopcount++; -unlock: - if (error != 0 || (flags & V_XSLEEP) != 0) - MNT_REL(mp); - MNT_IUNLOCK(mp); - return (error); + return (vn_start_write_locked(mp, flags)); } /* @@ -1639,8 +1650,7 @@ vfs_write_suspend(mp) * Request a filesystem to resume write operations. */ void -vfs_write_resume(mp) - struct mount *mp; +vfs_write_resume_flags(struct mount *mp, int flags) { MNT_ILOCK(mp); @@ -1652,10 +1662,25 @@ vfs_write_resume(mp) wakeup(&mp->mnt_writeopcount); wakeup(&mp->mnt_flag); curthread->td_pflags &= ~TDP_IGNSUSP; + if ((flags & VR_START_WRITE) != 0) { + MNT_REF(mp); + mp->mnt_writeopcount++; + } MNT_IUNLOCK(mp); VFS_SUSP_CLEAN(mp); - } else + } else if ((flags & VR_START_WRITE) != 0) { + MNT_REF(mp); + vn_start_write_locked(mp, 0); + } else { MNT_IUNLOCK(mp); + } +} + +void +vfs_write_resume(struct mount *mp) +{ + + vfs_write_resume_flags(mp, 0); } /* |