From e0cb5722e112811d32d600ef750f9b39e6f684ca Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Fri, 7 Jun 2024 21:02:06 -0400 Subject: [PATCH] bcachefs: Fix snapshot_create_lock lock ordering ====================================================== WARNING: possible circular locking dependency detected 6.10.0-rc2-ktest-00018-gebd1d148b278 #144 Not tainted ------------------------------------------------------ fio/1345 is trying to acquire lock: ffff88813e200ab8 (&c->snapshot_create_lock){++++}-{3:3}, at: bch2_truncate+0x76/0xf0 but task is already holding lock: ffff888105a1fa38 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}, at: do_truncate+0x7b/0xc0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}: down_write+0x3d/0xd0 bch2_write_iter+0x1c0/0x10f0 vfs_write+0x24a/0x560 __x64_sys_pwrite64+0x77/0xb0 x64_sys_call+0x17e5/0x1ab0 do_syscall_64+0x68/0x130 entry_SYSCALL_64_after_hwframe+0x4b/0x53 -> #1 (sb_writers#10){.+.+}-{0:0}: mnt_want_write+0x4a/0x1d0 filename_create+0x69/0x1a0 user_path_create+0x38/0x50 bch2_fs_file_ioctl+0x315/0xbf0 __x64_sys_ioctl+0x297/0xaf0 x64_sys_call+0x10cb/0x1ab0 do_syscall_64+0x68/0x130 entry_SYSCALL_64_after_hwframe+0x4b/0x53 -> #0 (&c->snapshot_create_lock){++++}-{3:3}: __lock_acquire+0x1445/0x25b0 lock_acquire+0xbd/0x2b0 down_read+0x40/0x180 bch2_truncate+0x76/0xf0 bchfs_truncate+0x240/0x3f0 bch2_setattr+0x7b/0xb0 notify_change+0x322/0x4b0 do_truncate+0x8b/0xc0 do_ftruncate+0x110/0x270 __x64_sys_ftruncate+0x43/0x80 x64_sys_call+0x1373/0x1ab0 do_syscall_64+0x68/0x130 entry_SYSCALL_64_after_hwframe+0x4b/0x53 other info that might help us debug this: Chain exists of: &c->snapshot_create_lock --> sb_writers#10 --> &sb->s_type->i_mutex_key#13 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sb->s_type->i_mutex_key#13); lock(sb_writers#10); lock(&sb->s_type->i_mutex_key#13); rlock(&c->snapshot_create_lock); *** DEADLOCK *** Signed-off-by: Kent Overstreet --- fs/bcachefs/fs-ioctl.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-) diff --git a/fs/bcachefs/fs-ioctl.c b/fs/bcachefs/fs-ioctl.c index 205a323ffc6ddd..3551a737181b2e 100644 --- a/fs/bcachefs/fs-ioctl.c +++ b/fs/bcachefs/fs-ioctl.c @@ -308,8 +308,8 @@ static int bch2_ioc_goingdown(struct bch_fs *c, u32 __user *arg) return ret; } -static long __bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp, - struct bch_ioctl_subvolume arg) +static long bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp, + struct bch_ioctl_subvolume arg) { struct inode *dir; struct bch_inode_info *inode; @@ -406,9 +406,12 @@ static long __bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp, !arg.src_ptr) snapshot_src.subvol = inode_inum(to_bch_ei(dir)).subvol; + down_write(&c->snapshot_create_lock); inode = __bch2_create(file_mnt_idmap(filp), to_bch_ei(dir), dst_dentry, arg.mode|S_IFDIR, 0, snapshot_src, create_flags); + up_write(&c->snapshot_create_lock); + error = PTR_ERR_OR_ZERO(inode); if (error) goto err3; @@ -429,16 +432,6 @@ static long __bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp, return error; } -static long bch2_ioctl_subvolume_create(struct bch_fs *c, struct file *filp, - struct bch_ioctl_subvolume arg) -{ - down_write(&c->snapshot_create_lock); - long ret = __bch2_ioctl_subvolume_create(c, filp, arg); - up_write(&c->snapshot_create_lock); - - return ret; -} - static long bch2_ioctl_subvolume_destroy(struct bch_fs *c, struct file *filp, struct bch_ioctl_subvolume arg) {