| From | Greg Kroah-Hartman <> | Subject | [PATCH 5.7 136/166] btrfs: discard: add missing put when grabbing block group from unused list | Date | Tue, 14 Jul 2020 20:45:01 +0200 |
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From: Qu Wenruo <wqu@suse.com>
commit 04e484c5973ed0f9234c97685c3c5e1ebf0d6eb6 upstream.
[BUG] The following small test script can trigger ASSERT() at unmount time:
mkfs.btrfs -f $dev mount $dev $mnt mount -o remount,discard=async $mnt umount $mnt
The call trace: assertion failed: atomic_read(&block_group->count) == 1, in fs/btrfs/block-group.c:3431 ------------[ cut here ]------------ kernel BUG at fs/btrfs/ctree.h:3204! invalid opcode: 0000 [#1] PREEMPT SMP NOPTI CPU: 4 PID: 10389 Comm: umount Tainted: G O 5.8.0-rc3-custom+ #68 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: btrfs_free_block_groups.cold+0x22/0x55 [btrfs] close_ctree+0x2cb/0x323 [btrfs] btrfs_put_super+0x15/0x17 [btrfs] generic_shutdown_super+0x72/0x110 kill_anon_super+0x18/0x30 btrfs_kill_super+0x17/0x30 [btrfs] deactivate_locked_super+0x3b/0xa0 deactivate_super+0x40/0x50 cleanup_mnt+0x135/0x190 __cleanup_mnt+0x12/0x20 task_work_run+0x64/0xb0 __prepare_exit_to_usermode+0x1bc/0x1c0 __syscall_return_slowpath+0x47/0x230 do_syscall_64+0x64/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xa9
The code: ASSERT(atomic_read(&block_group->count) == 1); btrfs_put_block_group(block_group);
[CAUSE] Obviously it's some btrfs_get_block_group() call doesn't get its put call.
The offending btrfs_get_block_group() happens here:
void btrfs_mark_bg_unused(struct btrfs_block_group *bg) { if (list_empty(&bg->bg_list)) { btrfs_get_block_group(bg); list_add_tail(&bg->bg_list, &fs_info->unused_bgs); } }
So every call sites removing the block group from unused_bgs list should reduce the ref count of that block group.
However for async discard, it didn't follow the call convention:
void btrfs_discard_punt_unused_bgs_list(struct btrfs_fs_info *fs_info) { list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs, bg_list) { list_del_init(&block_group->bg_list); btrfs_discard_queue_work(&fs_info->discard_ctl, block_group); } }
And in btrfs_discard_queue_work(), it doesn't call btrfs_put_block_group() either.
[FIX] Fix the problem by reducing the reference count when we grab the block group from unused_bgs list.
Reported-by: Marcos Paulo de Souza <mpdesouza@suse.com> Fixes: 6e80d4f8c422 ("btrfs: handle empty block_group removal for async discard") CC: stable@vger.kernel.org # 5.6+ Tested-by: Marcos Paulo de Souza <mpdesouza@suse.com> Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: Qu Wenruo <wqu@suse.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/discard.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/btrfs/discard.c +++ b/fs/btrfs/discard.c @@ -619,6 +619,7 @@ void btrfs_discard_punt_unused_bgs_list( list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs, bg_list) { list_del_init(&block_group->bg_list); + btrfs_put_block_group(block_group); btrfs_discard_queue_work(&fs_info->discard_ctl, block_group); } spin_unlock(&fs_info->unused_bgs_lock);
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