This is a note to let you know that I've just added the patch titled
fscache: Use wait_on_bit() to wait for the freeing of relinquished volume
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fscache-use-wait_on_bit-to-wait-for-the-freeing-of-r.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 97b1dc985ce1d6235a025671abbaf83173e3c1c5
Author: Hou Tao <houtao1@xxxxxxxxxx>
Date: Fri Jan 13 19:52:10 2023 +0800
fscache: Use wait_on_bit() to wait for the freeing of relinquished volume
[ Upstream commit 8226e37d82f43657da34dd770e2b38f20242ada7 ]
The freeing of relinquished volume will wake up the pending volume
acquisition by using wake_up_bit(), however it is mismatched with
wait_var_event() used in fscache_wait_on_volume_collision() and it will
never wake up the waiter in the wait-queue because these two functions
operate on different wait-queues.
According to the implementation in fscache_wait_on_volume_collision(),
if the wake-up of pending acquisition is delayed longer than 20 seconds
(e.g., due to the delay of on-demand fd closing), the first
wait_var_event_timeout() will timeout and the following wait_var_event()
will hang forever as shown below:
FS-Cache: Potential volume collision new=00000024 old=00000022
......
INFO: task mount:1148 blocked for more than 122 seconds.
Not tainted 6.1.0-rc6+ #1
task:mount state:D stack:0 pid:1148 ppid:1
Call Trace:
<TASK>
__schedule+0x2f6/0xb80
schedule+0x67/0xe0
fscache_wait_on_volume_collision.cold+0x80/0x82
__fscache_acquire_volume+0x40d/0x4e0
erofs_fscache_register_volume+0x51/0xe0 [erofs]
erofs_fscache_register_fs+0x19c/0x240 [erofs]
erofs_fc_fill_super+0x746/0xaf0 [erofs]
vfs_get_super+0x7d/0x100
get_tree_nodev+0x16/0x20
erofs_fc_get_tree+0x20/0x30 [erofs]
vfs_get_tree+0x24/0xb0
path_mount+0x2fa/0xa90
do_mount+0x7c/0xa0
__x64_sys_mount+0x8b/0xe0
do_syscall_64+0x30/0x60
entry_SYSCALL_64_after_hwframe+0x46/0xb0
Considering that wake_up_bit() is more selective, so fix it by using
wait_on_bit() instead of wait_var_event() to wait for the freeing of
relinquished volume. In addition because waitqueue_active() is used in
wake_up_bit() and clear_bit() doesn't imply any memory barrier, use
clear_and_wake_up_bit() to add the missing memory barrier between
cursor->flags and waitqueue_active().
Fixes: 62ab63352350 ("fscache: Implement volume registration")
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230113115211.2895845-2-houtao@xxxxxxxxxxxxxxx/ # v3
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c
index ab8ceddf9efa..903af9d85f8b 100644
--- a/fs/fscache/volume.c
+++ b/fs/fscache/volume.c
@@ -141,13 +141,14 @@ static bool fscache_is_acquire_pending(struct fscache_volume *volume)
static void fscache_wait_on_volume_collision(struct fscache_volume *candidate,
unsigned int collidee_debug_id)
{
- wait_var_event_timeout(&candidate->flags,
- !fscache_is_acquire_pending(candidate), 20 * HZ);
+ wait_on_bit_timeout(&candidate->flags, FSCACHE_VOLUME_ACQUIRE_PENDING,
+ TASK_UNINTERRUPTIBLE, 20 * HZ);
if (fscache_is_acquire_pending(candidate)) {
pr_notice("Potential volume collision new=%08x old=%08x",
candidate->debug_id, collidee_debug_id);
fscache_stat(&fscache_n_volumes_collision);
- wait_var_event(&candidate->flags, !fscache_is_acquire_pending(candidate));
+ wait_on_bit(&candidate->flags, FSCACHE_VOLUME_ACQUIRE_PENDING,
+ TASK_UNINTERRUPTIBLE);
}
}
@@ -347,8 +348,8 @@ static void fscache_wake_pending_volume(struct fscache_volume *volume,
hlist_bl_for_each_entry(cursor, p, h, hash_link) {
if (fscache_volume_same(cursor, volume)) {
fscache_see_volume(cursor, fscache_volume_see_hash_wake);
- clear_bit(FSCACHE_VOLUME_ACQUIRE_PENDING, &cursor->flags);
- wake_up_bit(&cursor->flags, FSCACHE_VOLUME_ACQUIRE_PENDING);
+ clear_and_wake_up_bit(FSCACHE_VOLUME_ACQUIRE_PENDING,
+ &cursor->flags);
return;
}
}
