60 lines
2.1 KiB
Diff
60 lines
2.1 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Rohan Puri <rohan.puri15@gmail.com>
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Date: Sat, 28 Jul 2018 18:32:12 +0530
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Subject: [PATCH] Fix deadlock between zfs umount & snapentry_expire
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zfs umount -> zfsctl_destroy() takes the zfs_snapshot_lock as a
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writer and calls zfsctl_snapshot_unmount_cancel(), which waits
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for snapentry_expire() if present (when snap is automounted).
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This snapentry_expire() itself then waits for zfs_snapshot_lock
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as a reader, resulting in a deadlock.
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The fix is to only hold the zfs_snapshot_lock over the tree
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lookup and removal. After a successful lookup the lock can
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be dropped and zfs_snapentry_t will remain valid until the
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reference taken by the lookup is released.
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Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
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Signed-off-by: Rohan Puri <rohan.puri15@gmail.com>
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Closes #7751
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Closes #7752
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(Cherry-picked from fd7265c646f40e364396af5014bbb83e809e124a)
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Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
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---
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module/zfs/zfs_ctldir.c | 11 +++++------
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1 file changed, 5 insertions(+), 6 deletions(-)
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diff --git a/module/zfs/zfs_ctldir.c b/module/zfs/zfs_ctldir.c
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index 3b5fb196..14af55c4 100644
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--- a/module/zfs/zfs_ctldir.c
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+++ b/module/zfs/zfs_ctldir.c
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@@ -358,8 +358,6 @@ snapentry_expire(void *data)
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static void
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zfsctl_snapshot_unmount_cancel(zfs_snapentry_t *se)
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{
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- ASSERT(RW_LOCK_HELD(&zfs_snapshot_lock));
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-
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if (taskq_cancel_id(system_delay_taskq, se->se_taskqid) == 0) {
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se->se_taskqid = TASKQID_INVALID;
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zfsctl_snapshot_rele(se);
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@@ -570,13 +568,14 @@ zfsctl_destroy(zfsvfs_t *zfsvfs)
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uint64_t objsetid = dmu_objset_id(zfsvfs->z_os);
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rw_enter(&zfs_snapshot_lock, RW_WRITER);
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- if ((se = zfsctl_snapshot_find_by_objsetid(spa, objsetid))
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- != NULL) {
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- zfsctl_snapshot_unmount_cancel(se);
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+ se = zfsctl_snapshot_find_by_objsetid(spa, objsetid);
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+ if (se != NULL)
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zfsctl_snapshot_remove(se);
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+ rw_exit(&zfs_snapshot_lock);
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+ if (se != NULL) {
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+ zfsctl_snapshot_unmount_cancel(se);
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zfsctl_snapshot_rele(se);
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}
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- rw_exit(&zfs_snapshot_lock);
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} else if (zfsvfs->z_ctldir) {
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iput(zfsvfs->z_ctldir);
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zfsvfs->z_ctldir = NULL;
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