We found a hungtask problem as described following:
Running xfstests generic/390 with ext4 filesystem, and simutaneously
offline/onlines the disk we tested. It will cause a hungtask problem
whose call trace is like this,
[369.857104] INFO: task fsstress:11672 blocked for more than 120 seconds.
[ 369.875724] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 369.885168] fsstress D 0 11672 11625 0x00000080
[ 369.885169] Call Trace:
[ 369.885171] ? __schedule+0x2fc/0x930
[ 369.885173] ? filename_parentat+0x10b/0x1a0
[ 369.885175] schedule+0x28/0x70
[ 369.885176] rwsem_down_read_failed+0x102/0x1c0
[ 369.885178] ? __percpu_down_read+0x93/0xb0
[ 369.885179] __percpu_down_read+0x93/0xb0
[ 369.885182] __sb_start_write+0x5f/0x70
[ 369.885183] mnt_want_write+0x20/0x50
[ 369.885184] do_renameat2+0x1f3/0x550
[ 369.885186] __x64_sys_rename+0x1c/0x20
[ 369.885187] do_syscall_64+0x5b/0x1b0
[ 369.885188] entry_SYSCALL_64_after_hwframe+0x65/0xca
[ 369.885189] RIP: 0033:0x7f5e6e34ccb7
[ 369.885190] Code: Bad RIP value.
[ 369.885191] RSP: 002b:00007ffef4a83788 EFLAGS: 00000206 ORIG_RAX: 0000000000000052
[ 369.885191] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5e6e34ccb7
[ 369.885192] RDX: 0000000000000000 RSI: 0000000001b09500 RDI: 0000000001b09f90
[ 369.885192] RBP: 0000000000000000 R08: 0000000000000021 R09: 0000000000000000
[ 369.885193] R10: 0000000000000692 R11: 0000000000000206 R12: 00007ffef4a83a30
[ 369.885193] R13: 00007ffef4a83a40 R14: 00007ffef4a83a40 R15: 0000000000000001
The root cause is that when offline/onlines disks, the filesystem can easily get into
a error state and this makes it change to be read-only. Function freeze_super() will hold
all sb_writers rwsems including rwsem of SB_FREEZE_WRITE when filesystem not read-only,
but thaw_super_locked() cannot release these while the filesystem suddenly become read-only,
because the logic will go to out.
freeze_super
hold sb_writers rwsems
sb->s_writers.frozen = SB_FREEZE_COMPLETE
thaw_super_locked
sb_rdonly
sb->s_writers.frozen = SB_UNFROZEN;
goto out // not release rwsems
And at this time, if we call mnt_want_write(), the process will be blocked.
This patch fixes this problem, when filesystem is read-only, just not to set sb_writers.frozen
be SB_FREEZE_COMPLETE in freeze_super() and then release all rwsems in thaw_super_locked.
Signed-off-by: Shijie Luo <luoshijie1@xxxxxxxxxx>
Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx>
Fix some descriptions errors and resend the patch.
---
fs/super.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 2c6cdea2ab2d..50d79213f678 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1672,9 +1672,7 @@ int freeze_super(struct super_block *sb)
}
if (sb_rdonly(sb)) {
- /* Nothing to do really... */
- sb->s_writers.frozen = SB_FREEZE_COMPLETE;
- up_write(&sb->s_umount);
+ deactivate_locked_super(sb);
return 0;
}
@@ -1733,13 +1731,11 @@ static int thaw_super_locked(struct super_block *sb)
return -EINVAL;
}
- if (sb_rdonly(sb)) {
- sb->s_writers.frozen = SB_UNFROZEN;
- goto out;
- }
-
lockdep_sb_freeze_acquire(sb);
+ if (sb_rdonly(sb))
+ goto out;
+
if (sb->s_op->unfreeze_fs) {
error = sb->s_op->unfreeze_fs(sb);
if (error) {
@@ -1751,9 +1747,9 @@ static int thaw_super_locked(struct super_block *sb)
}
}
+out:
sb->s_writers.frozen = SB_UNFROZEN;
sb_freeze_unlock(sb);
-out:
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);
return 0;
--
2.19.1
