[PATCH 5.16 232/285] btrfs: zoned: traverse devices under chunk_mutex in btrfs_can_activate_zone

Greg Kroah-Hartman
2022-04-12T08:07:24Z

From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

commit 0b9e66762aa0cda2a9c2d5542d64e04dac528fa6 upstream.

btrfs_can_activate_zone() can be called with the device_list_mutex already
held, which will lead to a deadlock:

insert_dev_extents() // Takes device_list_mutex
`-> insert_dev_extent()
`-> btrfs_insert_empty_item()
`-> btrfs_insert_empty_items()
`-> btrfs_search_slot()
`-> btrfs_cow_block()
`-> __btrfs_cow_block()
`-> btrfs_alloc_tree_block()
`-> btrfs_reserve_extent()
`-> find_free_extent()
`-> find_free_extent_update_loop()
`-> can_allocate_chunk()
`-> btrfs_can_activate_zone() // Takes device_list_mutex again

Instead of using the RCU on fs_devices->device_list we
can use fs_devices->alloc_list, protected by the chunk_mutex to traverse
the list of active devices.

We are in the chunk allocation thread. The newer chunk allocation
happens from the devices in the fs_device->alloc_list protected by the
chunk_mutex.

btrfs_create_chunk()
lockdep_assert_held(&info->chunk_mutex);
gather_device_info
list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list)

Also, a device that reappears after the mount won't join the alloc_list
yet and, it will be in the dev_list, which we don't want to consider in
the context of the chunk alloc.

[15.166572] WARNING: possible recursive locking detected
[15.167117] 5.17.0-rc6-dennis #79 Not tainted
[15.167487] --------------------------------------------
[15.167733] kworker/u8:3/146 is trying to acquire lock:
[15.167733] ffff888102962ee0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: find_free_extent+0x15a/0x14f0 [btrfs]
[15.167733]
[15.167733] but task is already holding lock:
[15.167733] ffff888102962ee0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: btrfs_create_pending_block_groups+0x20a/0x560 [btrfs]
[15.167733]
[15.167733] other info that might help us debug this:
[15.167733] Possible unsafe locking scenario:
[15.167733]
[15.171834] CPU0
[15.171834] ----
[15.171834] lock(&fs_devs->device_list_mutex);
[15.171834] lock(&fs_devs->device_list_mutex);
[15.171834]
[15.171834] *** DEADLOCK ***
[15.171834]
[15.171834] May be due to missing lock nesting notation
[15.171834]
[15.171834] 5 locks held by kworker/u8:3/146:
[15.171834] #0: ffff888100050938 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x1c3/0x5a0
[15.171834] #1: ffffc9000067be80 ((work_completion)(&fs_info->async_data_reclaim_work)){+.+.}-{0:0}, at: process_one_work+0x1c3/0x5a0
[15.176244] #2: ffff88810521e620 (sb_internal){.+.+}-{0:0}, at: flush_space+0x335/0x600 [btrfs]
[15.176244] #3: ffff888102962ee0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: btrfs_create_pending_block_groups+0x20a/0x560 [btrfs]
[15.176244] #4: ffff8881152e4b78 (btrfs-dev-00){++++}-{3:3}, at: __btrfs_tree_lock+0x27/0x130 [btrfs]
[15.179641]
[15.179641] stack backtrace:
[15.179641] CPU: 1 PID: 146 Comm: kworker/u8:3 Not tainted 5.17.0-rc6-dennis #79
[15.179641] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35 04/01/2014
[15.179641] Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]
[15.179641] Call Trace:
[15.179641] <TASK>
[15.179641] dump_stack_lvl+0x45/0x59
[15.179641] __lock_acquire.cold+0x217/0x2b2
[15.179641] lock_acquire+0xbf/0x2b0
[15.183838] ? find_free_extent+0x15a/0x14f0 [btrfs]
[15.183838] __mutex_lock+0x8e/0x970
[15.183838] ? find_free_extent+0x15a/0x14f0 [btrfs]
[15.183838] ? find_free_extent+0x15a/0x14f0 [btrfs]
[15.183838] ? lock_is_held_type+0xd7/0x130
[15.183838] ? find_free_extent+0x15a/0x14f0 [btrfs]
[15.183838] find_free_extent+0x15a/0x14f0 [btrfs]
[15.183838] ? _raw_spin_unlock+0x24/0x40
[15.183838] ? btrfs_get_alloc_profile+0x106/0x230 [btrfs]
[15.187601] btrfs_reserve_extent+0x131/0x260 [btrfs]
[15.187601] btrfs_alloc_tree_block+0xb5/0x3b0 [btrfs]
[15.187601] __btrfs_cow_block+0x138/0x600 [btrfs]
[15.187601] btrfs_cow_block+0x10f/0x230 [btrfs]
[15.187601] btrfs_search_slot+0x55f/0xbc0 [btrfs]
[15.187601] ? lock_is_held_type+0xd7/0x130
[15.187601] btrfs_insert_empty_items+0x2d/0x60 [btrfs]
[15.187601] btrfs_create_pending_block_groups+0x2b3/0x560 [btrfs]
[15.187601] __btrfs_end_transaction+0x36/0x2a0 [btrfs]
[15.192037] flush_space+0x374/0x600 [btrfs]
[15.192037] ? find_held_lock+0x2b/0x80
[15.192037] ? btrfs_async_reclaim_data_space+0x49/0x180 [btrfs]
[15.192037] ? lock_release+0x131/0x2b0
[15.192037] btrfs_async_reclaim_data_space+0x70/0x180 [btrfs]
[15.192037] process_one_work+0x24c/0x5a0
[15.192037] worker_thread+0x4a/0x3d0

Fixes: a85f05e59bc1 ("btrfs: zoned: avoid chunk allocation if active block group has enough space")
CC: stable@vger.kernel.org # 5.16+
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/zoned.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -1936,18 +1936,19 @@ int btrfs_zone_finish(struct btrfs_block

bool btrfs_can_activate_zone(struct btrfs_fs_devices *fs_devices, u64 flags)
{
+ struct btrfs_fs_info *fs_info = fs_devices->fs_info;
struct btrfs_device *device;
bool ret = false;

- if (!btrfs_is_zoned(fs_devices->fs_info))
+ if (!btrfs_is_zoned(fs_info))
return true;

/* Non-single profiles are not supported yet */
ASSERT((flags & BTRFS_BLOCK_GROUP_PROFILE_MASK) == 0);

/* Check if there is a device with active zones left */
- mutex_lock(&fs_devices->device_list_mutex);
- list_for_each_entry(device, &fs_devices->devices, dev_list) {
+ mutex_lock(&fs_info->chunk_mutex);
+ list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
struct btrfs_zoned_device_info *zinfo = device->zone_info;

if (!device->bdev)
@@ -1959,7 +1960,7 @@ bool btrfs_can_activate_zone(struct btrf
break;
}
}
- mutex_unlock(&fs_devices->device_list_mutex);
+ mutex_unlock(&fs_info->chunk_mutex);

return ret;
}