From 6e37d245994189ba757df7dc2950a44d31421ac6 Mon Sep 17 00:00:00 2001 From: Johannes Thumshirn Date: Wed, 17 Feb 2021 16:06:18 +0900 Subject: [PATCH] btrfs: zoned: fix deadlock on log sync Lockdep with fstests test case btrfs/041 detected a unsafe locking scenario when we allocate the log node on a zoned filesystem. btrfs/041 ============================================ WARNING: possible recursive locking detected 5.11.0-rc7+ #939 Not tainted -------------------------------------------- xfs_io/698 is trying to acquire lock: ffff88810cd673a0 (&root->log_mutex){+.+.}-{3:3}, at: btrfs_sync_log+0x3d1/0xee0 [btrfs] but task is already holding lock: ffff88810b0fc3a0 (&root->log_mutex){+.+.}-{3:3}, at: btrfs_sync_log+0x313/0xee0 [btrfs] other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&root->log_mutex); lock(&root->log_mutex); *** DEADLOCK *** May be due to missing lock nesting notation 2 locks held by xfs_io/698: #0: ffff88810cd66620 (sb_internal){.+.+}-{0:0}, at: btrfs_sync_file+0x2c3/0x570 [btrfs] #1: ffff88810b0fc3a0 (&root->log_mutex){+.+.}-{3:3}, at: btrfs_sync_log+0x313/0xee0 [btrfs] stack backtrace: CPU: 0 PID: 698 Comm: xfs_io Not tainted 5.11.0-rc7+ #939 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4-rebuilt.opensuse.org 04/01/2014 Call Trace: dump_stack+0x77/0x97 __lock_acquire.cold+0xb9/0x32a lock_acquire+0xb5/0x400 ? btrfs_sync_log+0x3d1/0xee0 [btrfs] __mutex_lock+0x7b/0x8d0 ? btrfs_sync_log+0x3d1/0xee0 [btrfs] ? btrfs_sync_log+0x3d1/0xee0 [btrfs] ? find_first_extent_bit+0x9f/0x100 [btrfs] ? __mutex_unlock_slowpath+0x35/0x270 btrfs_sync_log+0x3d1/0xee0 [btrfs] btrfs_sync_file+0x3a8/0x570 [btrfs] __x64_sys_fsync+0x34/0x60 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 This happens, because we are taking the ->log_mutex albeit it has already been locked. Also while at it, fix the bogus unlock of the tree_log_mutex in the error handling. Fixes: 3ddebf27fcd3 ("btrfs: zoned: reorder log node allocation on zoned filesystem") Reviewed-by: Filipe Manana Signed-off-by: Johannes Thumshirn Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/tree-log.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index d90695c1ab6c..2f1acc9aea9e 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -3174,16 +3174,13 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, root_log_ctx.log_transid = log_root_tree->log_transid; if (btrfs_is_zoned(fs_info)) { - mutex_lock(&fs_info->tree_root->log_mutex); if (!log_root_tree->node) { ret = btrfs_alloc_log_tree_node(trans, log_root_tree); if (ret) { - mutex_unlock(&fs_info->tree_log_mutex); mutex_unlock(&log_root_tree->log_mutex); goto out; } } - mutex_unlock(&fs_info->tree_root->log_mutex); } /*