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Cherry-pick fix for deadlock umount/snapentry_expire

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Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
This commit is contained in:
Stoiko Ivanov 2018-08-03 11:51:15 +02:00 committed by Dietmar Maurer
parent afa7541760
commit 76a4c29ab5
2 changed files with 60 additions and 0 deletions
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59
zfs-patches/0005-Fix-deadlock-between-zfs-umount-snapentry_expire.patch Normal file
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@ -0,0 +1,59 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Rohan Puri <rohan.puri15@gmail.com>
Date: Sat, 28 Jul 2018 18:32:12 +0530
Subject: [PATCH] Fix deadlock between zfs umount & snapentry_expire
zfs umount -> zfsctl_destroy() takes the zfs_snapshot_lock as a
writer and calls zfsctl_snapshot_unmount_cancel(), which waits
for snapentry_expire() if present (when snap is automounted).
This snapentry_expire() itself then waits for zfs_snapshot_lock
as a reader, resulting in a deadlock.
The fix is to only hold the zfs_snapshot_lock over the tree
lookup and removal. After a successful lookup the lock can
be dropped and zfs_snapentry_t will remain valid until the
reference taken by the lookup is released.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rohan Puri <rohan.puri15@gmail.com>
Closes #7751
Closes #7752
(Cherry-picked from fd7265c646f40e364396af5014bbb83e809e124a)
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
---
module/zfs/zfs_ctldir.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/module/zfs/zfs_ctldir.c b/module/zfs/zfs_ctldir.c
index 3b5fb196..14af55c4 100644
--- a/module/zfs/zfs_ctldir.c
+++ b/module/zfs/zfs_ctldir.c
@@ -358,8 +358,6 @@ snapentry_expire(void *data)
static void
zfsctl_snapshot_unmount_cancel(zfs_snapentry_t *se)
{
- ASSERT(RW_LOCK_HELD(&zfs_snapshot_lock));
-
if (taskq_cancel_id(system_delay_taskq, se->se_taskqid) == 0) {
se->se_taskqid = TASKQID_INVALID;
zfsctl_snapshot_rele(se);
@@ -570,13 +568,14 @@ zfsctl_destroy(zfsvfs_t *zfsvfs)
uint64_t objsetid = dmu_objset_id(zfsvfs->z_os);
rw_enter(&zfs_snapshot_lock, RW_WRITER);
- if ((se = zfsctl_snapshot_find_by_objsetid(spa, objsetid))
- != NULL) {
- zfsctl_snapshot_unmount_cancel(se);
+ se = zfsctl_snapshot_find_by_objsetid(spa, objsetid);
+ if (se != NULL)
zfsctl_snapshot_remove(se);
+ rw_exit(&zfs_snapshot_lock);
+ if (se != NULL) {
+ zfsctl_snapshot_unmount_cancel(se);
zfsctl_snapshot_rele(se);
}
- rw_exit(&zfs_snapshot_lock);
} else if (zfsvfs->z_ctldir) {
iput(zfsvfs->z_ctldir);
zfsvfs->z_ctldir = NULL;

1
zfs-patches/series
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@ -2,3 +2,4 @@
0002-import-with-d-dev-disk-by-id-in-scan-service.patch
0003-always-load-ZFS-module-on-boot.patch
0004-Fix-zpl_mount-deadlock.patch
0005-Fix-deadlock-between-zfs-umount-snapentry_expire.patch