Greetings,
Using openSUSE's "partitioner" gizmo to set up a reiserfs partition with
quotas and whatnot enabled rewarded me with a deadlock.
In reiserfs/lock.c we see:
...
* Also this lock is often released before a call that could block because
* reiserfs performances were partially based on the release while schedule()
* property of the Bkl.
*/
void reiserfs_write_lock(struct super_block *s)
And in the problematic reiserfs_fill_super():
/*
* This function is called with the bkl, which also was the old
* locking used here.
* do_journal_begin() will soon check if we hold the lock (ie: was the
* bkl). This is likely because do_journal_begin() has several another
* callers because at this time, it doesn't seem to be necessary to
* protect against anything.
* Anyway, let's be conservative and lock for now.
*/
reiserfs_write_lock(s);
Given wishy-washy "be conservative for now", and "this lock is often
released before a call that could block", it seemed reasonable to trade
a little conservatism for a chance to return from the blocking
function.
If we hold the super block lock while calling reiserfs_quota_on_mount(), we can
deadlock - mount blocks kworker/3:2, and sleeps forever more.
crash> ps|grep UN
715 2 3 ffff880220734d30 UN 0.0 0 0 [kworker/3:2]
9369 9341 2 ffff88021ffb7560 UN 1.3 493404 123184 Xorg
9665 9664 3 ffff880225b92ab0 UN 0.0 47368 812 udisks-daemon
10635 10403 3 ffff880222f22c70 UN 0.0 14904 936 mount
crash> bt ffff880220734d30
PID: 715 TASK: ffff880220734d30 CPU: 3 COMMAND: "kworker/3:2"
#0 [ffff8802244c3c20] schedule at ffffffff8144584b
#1 [ffff8802244c3cc8] __rt_mutex_slowlock at ffffffff814472b3
#2 [ffff8802244c3d28] rt_mutex_slowlock at ffffffff814473f5
#3 [ffff8802244c3dc8] reiserfs_write_lock at ffffffffa05f28fd [reiserfs]
#4 [ffff8802244c3de8] flush_async_commits at ffffffffa05ec91d [reiserfs]
#5 [ffff8802244c3e08] process_one_work at ffffffff81073726
#6 [ffff8802244c3e68] worker_thread at ffffffff81073eba
#7 [ffff8802244c3ec8] kthread at ffffffff810782e0
#8 [ffff8802244c3f48] kernel_thread_helper at ffffffff81450064
crash> struct rt_mutex ffff880222e8f628
struct rt_mutex {
wait_lock = {
raw_lock = {
slock = 65537
}
},
wait_list = {
node_list = {
next = 0xffff8802244c3d48,
prev = 0xffff8802244c3d48
}
},
owner = 0xffff880222f22c71,
save_state = 0
}
crash> bt 0xffff880222f22c70
PID: 10635 TASK: ffff880222f22c70 CPU: 3 COMMAND: "mount"
#0 [ffff8802216a9868] schedule at ffffffff8144584b
#1 [ffff8802216a9910] schedule_timeout at ffffffff81446865
#2 [ffff8802216a99a0] wait_for_common at ffffffff81445f74
#3 [ffff8802216a9a30] flush_work at ffffffff810712d3
#4 [ffff8802216a9ab0] schedule_on_each_cpu at ffffffff81074463
#5 [ffff8802216a9ae0] invalidate_bdev at ffffffff81178aba
#6 [ffff8802216a9af0] vfs_load_quota_inode at ffffffff811a3632
#7 [ffff8802216a9b50] dquot_quota_on_mount at ffffffff811a375c
#8 [ffff8802216a9b80] finish_unfinished at ffffffffa05dd8b0 [reiserfs]
#9 [ffff8802216a9cc0] reiserfs_fill_super at ffffffffa05de825 [reiserfs]
#10 [ffff8802216a9d90] mount_bdev at ffffffff8114c93f
#11 [ffff8802216a9e00] mount_fs at ffffffff8114d035
#12 [ffff8802216a9e50] vfs_kern_mount at ffffffff81167d36
#13 [ffff8802216a9e90] do_kern_mount at ffffffff811692c3
#14 [ffff8802216a9ed0] do_mount at ffffffff8116adb5
#15 [ffff8802216a9f30] sys_mount at ffffffff8116b25a
#16 [ffff8802216a9f80] system_call_fastpath at ffffffff8144ef12
RIP: 00007f7b9303997a RSP: 00007ffff443c7a8 RFLAGS: 00010202
RAX: 00000000000000a5 RBX: ffffffff8144ef12 RCX: 00007f7b932e9ee0
RDX: 00007f7b93d9a400 RSI: 00007f7b93d9a3e0 RDI: 00007f7b93d9a3c0
RBP: 00007f7b93d9a2c0 R8: 00007f7b93d9a550 R9: 0000000000000001
R10: ffffffffc0ed040e R11: 0000000000000202 R12: 000000000000040e
R13: 0000000000000000 R14: 00000000c0ed040e R15: 00007ffff443ca20
ORIG_RAX: 00000000000000a5 CS: 0033 SS: 002b
Signed-off-by: Mike Galbraith <efault@xxxxxx>
---
fs/reiserfs/super.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -140,7 +140,13 @@ static int remove_save_link_only(struct
static int reiserfs_quota_on_mount(struct super_block *, int);
#endif
-/* look for uncompleted unlinks and truncates and complete them */
+/*
+ *look for uncompleted unlinks and truncates and complete them
+ *
+ * Called with super_block write locked. If quotas are enabled,
+ * we have to release/retake lest we call dquot_quota_on_mount(),
+ * proceed to schedule_on_each_cpu() and deadlock our own worker.
+ */
static int finish_unfinished(struct super_block *s)
{
INITIALIZE_PATH(path);
@@ -187,7 +193,9 @@ static int finish_unfinished(struct supe
quota_enabled[i] = 0;
continue;
}
+ reiserfs_write_unlock(s);
ret = reiserfs_quota_on_mount(s, i);
+ reiserfs_write_lock(s);
if (ret < 0)
reiserfs_warning(s, "reiserfs-2500",
"cannot turn on journaled "
--
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