| Message ID | 20230113115211.2895845-2-houtao@huaweicloud.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fixes for fscache volume operations | expand |
On Fri, 2023-01-13 at 19:52 +0800, Hou Tao wrote: > From: Hou Tao <houtao1@huawei.com> > > 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@linux.alibaba.com> > Signed-off-by: Hou Tao <houtao1@huawei.com> > --- > fs/fscache/volume.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > 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; > } > } Reviewed-by: Jeff Layton <jlayton@kernel.org>
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; } }