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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id j202sm6765637qke.108.2020.11.13.08.23.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2020 08:23:37 -0800 (PST) From: Josef Bacik To: linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: [PATCH v2 02/42] btrfs: fix lockdep splat in btrfs_recover_relocation Date: Fri, 13 Nov 2020 11:22:52 -0500 Message-Id: <44c756daa28122f0f51f52d154c1232a09e66872.1605284383.git.josef@toxicpanda.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org While testing the error paths of relocation I hit the following lockdep splat ====================================================== WARNING: possible circular locking dependency detected 5.10.0-rc2-btrfs-next-71 #1 Not tainted ------------------------------------------------------ find/324157 is trying to acquire lock: ffff8ebc48d293a0 (btrfs-tree-01#2/3){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] but task is already holding lock: ffff8eb9932c5088 (btrfs-tree-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (btrfs-tree-00){++++}-{3:3}: lock_acquire+0xd8/0x490 down_write_nested+0x44/0x120 __btrfs_tree_lock+0x27/0x120 [btrfs] btrfs_search_slot+0x2a3/0xc50 [btrfs] btrfs_insert_empty_items+0x58/0xa0 [btrfs] insert_with_overflow+0x44/0x110 [btrfs] btrfs_insert_xattr_item+0xb8/0x1d0 [btrfs] btrfs_setxattr+0xd6/0x4c0 [btrfs] btrfs_setxattr_trans+0x68/0x100 [btrfs] __vfs_setxattr+0x66/0x80 __vfs_setxattr_noperm+0x70/0x200 vfs_setxattr+0x6b/0x120 setxattr+0x125/0x240 path_setxattr+0xba/0xd0 __x64_sys_setxattr+0x27/0x30 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #0 (btrfs-tree-01#2/3){++++}-{3:3}: check_prev_add+0x91/0xc60 __lock_acquire+0x1689/0x3130 lock_acquire+0xd8/0x490 down_read_nested+0x45/0x220 __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] btrfs_next_old_leaf+0x27d/0x580 [btrfs] btrfs_real_readdir+0x1e3/0x4b0 [btrfs] iterate_dir+0x170/0x1c0 __x64_sys_getdents64+0x83/0x140 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(btrfs-tree-00); lock(btrfs-tree-01#2/3); lock(btrfs-tree-00); lock(btrfs-tree-01#2/3); *** DEADLOCK *** 5 locks held by find/324157: #0: ffff8ebc502c6e00 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x4d/0x60 #1: ffff8eb97f689980 (&type->i_mutex_dir_key#10){++++}-{3:3}, at: iterate_dir+0x52/0x1c0 #2: ffff8ebaec00ca58 (btrfs-tree-02#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] #3: ffff8eb98f986f78 (btrfs-tree-01#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] #4: ffff8eb9932c5088 (btrfs-tree-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] stack backtrace: CPU: 2 PID: 324157 Comm: find Not tainted 5.10.0-rc2-btrfs-next-71 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack+0x8d/0xb5 check_noncircular+0xff/0x110 ? mark_lock.part.0+0x468/0xe90 check_prev_add+0x91/0xc60 __lock_acquire+0x1689/0x3130 ? kvm_clock_read+0x14/0x30 ? kvm_sched_clock_read+0x5/0x10 lock_acquire+0xd8/0x490 ? __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] down_read_nested+0x45/0x220 ? __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] __btrfs_tree_read_lock+0x32/0x1a0 [btrfs] btrfs_next_old_leaf+0x27d/0x580 [btrfs] btrfs_real_readdir+0x1e3/0x4b0 [btrfs] iterate_dir+0x170/0x1c0 __x64_sys_getdents64+0x83/0x140 ? filldir+0x1d0/0x1d0 do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xa9 This is thankfully straightforward to fix, simply release the path before we setup the reloc_ctl. Signed-off-by: Josef Bacik --- fs/btrfs/volumes.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index bb1aa96e1233..ece8bb62fcc1 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -4283,6 +4283,8 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info) btrfs_warn(fs_info, "balance: cannot set exclusive op status, resume manually"); + btrfs_release_path(path); + mutex_lock(&fs_info->balance_mutex); BUG_ON(fs_info->balance_ctl); spin_lock(&fs_info->balance_lock);