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https://github.com/freebsd/freebsd-src
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There are several code sequences like
vfs_busy(mp); vfs_write_suspend(mp); which are problematic if other thread starts unmount between two calls. The unmount starts a write, while vfs_write_suspend() drain writers. On the other hand, unmount drains busy references, causing the deadlock. Add a flag argument to vfs_write_suspend and require the callers of it to specify VS_SKIP_UNMOUNT flag, when the call is performed not in the mount path, i.e. the covered vnode is not locked. The suspension is not attempted if VS_SKIP_UNMOUNT is specified and unmount is in progress. Reported and tested by: Andreas Longwitz <longwitz@incore.de> Sponsored by: The FreeBSD Foundation MFC after: 3 weeks
This commit is contained in:
parent
b71f585303
commit
cc3d8c35f5
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=253106
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@ -2960,7 +2960,7 @@ g_journal_do_switch(struct g_class *classp)
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GJ_TIMER_STOP(1, &bt, "BIO_FLUSH time of %s", sc->sc_name);
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GJ_TIMER_START(1, &bt);
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error = vfs_write_suspend(mp);
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error = vfs_write_suspend(mp, VS_SKIP_UNMOUNT);
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GJ_TIMER_STOP(1, &bt, "Suspend time of %s", mountpoint);
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if (error != 0) {
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GJ_DEBUG(0, "Cannot suspend file system %s (error=%d).",
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@ -1668,8 +1668,7 @@ vn_finished_secondary_write(mp)
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* Request a filesystem to suspend write operations.
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*/
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int
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vfs_write_suspend(mp)
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struct mount *mp;
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vfs_write_suspend(struct mount *mp, int flags)
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{
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int error;
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@ -1680,6 +1679,21 @@ vfs_write_suspend(mp)
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}
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while (mp->mnt_kern_flag & MNTK_SUSPEND)
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msleep(&mp->mnt_flag, MNT_MTX(mp), PUSER - 1, "wsuspfs", 0);
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/*
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* Unmount holds a write reference on the mount point. If we
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* own busy reference and drain for writers, we deadlock with
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* the reference draining in the unmount path. Callers of
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* vfs_write_suspend() must specify VS_SKIP_UNMOUNT if
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* vfs_busy() reference is owned and caller is not in the
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* unmount context.
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*/
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if ((flags & VS_SKIP_UNMOUNT) != 0 &&
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(mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) {
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MNT_IUNLOCK(mp);
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return (EBUSY);
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}
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mp->mnt_kern_flag |= MNTK_SUSPEND;
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mp->mnt_susp_owner = curthread;
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if (mp->mnt_writeopcount > 0)
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@ -398,6 +398,9 @@ extern int vttoif_tab[];
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#define VR_START_WRITE 0x0001 /* vfs_write_resume: start write atomically */
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#define VR_NO_SUSPCLR 0x0002 /* vfs_write_resume: do not clear suspension */
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#define VS_SKIP_UNMOUNT 0x0001 /* vfs_write_suspend: fail if the
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filesystem is being unmounted */
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#define VREF(vp) vref(vp)
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#ifdef DIAGNOSTIC
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@ -711,7 +714,7 @@ int vn_io_fault_pgmove(vm_page_t ma[], vm_offset_t offset, int xfersize,
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int vfs_cache_lookup(struct vop_lookup_args *ap);
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void vfs_timestamp(struct timespec *);
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void vfs_write_resume(struct mount *mp, int flags);
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int vfs_write_suspend(struct mount *mp);
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int vfs_write_suspend(struct mount *mp, int flags);
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int vop_stdbmap(struct vop_bmap_args *);
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int vop_stdfsync(struct vop_fsync_args *);
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int vop_stdgetwritemount(struct vop_getwritemount_args *);
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@ -423,7 +423,7 @@ ffs_snapshot(mp, snapfile)
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*/
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for (;;) {
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vn_finished_write(wrtmp);
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if ((error = vfs_write_suspend(vp->v_mount)) != 0) {
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if ((error = vfs_write_suspend(vp->v_mount, 0)) != 0) {
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vn_start_write(NULL, &wrtmp, V_WAIT);
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vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
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goto out;
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@ -206,7 +206,7 @@ ffs_susp_suspend(struct mount *mp)
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return (EPERM);
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#endif
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if ((error = vfs_write_suspend(mp)) != 0)
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if ((error = vfs_write_suspend(mp, VS_SKIP_UNMOUNT)) != 0)
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return (error);
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ump->um_writesuspended = 1;
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@ -257,7 +257,7 @@ ffs_mount(struct mount *mp)
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return (error);
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for (;;) {
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vn_finished_write(mp);
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if ((error = vfs_write_suspend(mp)) != 0)
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if ((error = vfs_write_suspend(mp, 0)) != 0)
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return (error);
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MNT_ILOCK(mp);
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if (mp->mnt_kern_flag & MNTK_SUSPENDED) {
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*/
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for (;;) {
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vn_finished_write(mp);
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if ((error = vfs_write_suspend(mp)) != 0)
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if ((error = vfs_write_suspend(mp, 0)) != 0)
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return (error);
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MNT_ILOCK(mp);
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if (mp->mnt_kern_flag & MNTK_SUSPENDED) {
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