Setting a large xattr value may require writing the attribute contents
to an external inode. In this case we may need to lock the xattr inode
along with the parent inode. This doesn't pose a deadlock risk because
xattr inodes are not directly visible to the user and their access is
restricted.
Assign a lockdep subclass to xattr inode's lock.
============================================
WARNING: possible recursive locking detected
4.12.0-rc1+ #740 Not tainted
--------------------------------------------
python/1822 is trying to acquire lock:
(&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff804912ca>] ext4_xattr_set_entry+0x65a/0x7b0
but task is already holding lock:
(&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&sb->s_type->i_mutex_key#15);
lock(&sb->s_type->i_mutex_key#15);
*** DEADLOCK ***
May be due to missing lock nesting notation
4 locks held by python/1822:
#0: (sb_writers#10){.+.+.+}, at: [<ffffffff803d0eef>] mnt_want_write+0x1f/0x50
#1: (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0
#2: (jbd2_handle){.+.+..}, at: [<ffffffff80493f40>] start_this_handle+0xf0/0x420
#3: (&ei->xattr_sem){++++..}, at: [<ffffffff804920ba>] ext4_xattr_set_handle+0x9a/0x4f0
stack backtrace:
CPU: 0 PID: 1822 Comm: python Not tainted 4.12.0-rc1+ #740
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
dump_stack+0x67/0x9e
__lock_acquire+0x5f3/0x1750
lock_acquire+0xb5/0x1d0
down_write+0x2c/0x60
ext4_xattr_set_entry+0x65a/0x7b0
ext4_xattr_block_set+0x1b2/0x9b0
ext4_xattr_set_handle+0x322/0x4f0
ext4_xattr_set+0x144/0x1a0
ext4_xattr_user_set+0x34/0x40
__vfs_setxattr+0x66/0x80
__vfs_setxattr_noperm+0x69/0x1c0
vfs_setxattr+0xa2/0xb0
setxattr+0x12e/0x150
path_setxattr+0x87/0xb0
SyS_setxattr+0xf/0x20
entry_SYSCALL_64_fastpath+0x18/0xad
Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>
---
fs/ext4/inode.c | 2 ++
fs/ext4/xattr.c | 8 ++++++++
fs/ext4/xattr.h | 6 ++++++
3 files changed, 16 insertions(+)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e5535e5b3dc5..d095bf7ad390 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4877,6 +4877,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
}
brelse(iloc.bh);
ext4_set_inode_flags(inode);
+ if (ei->i_flags & EXT4_EA_INODE_FL)
+ ext4_xattr_inode_set_class(inode);
unlock_new_inode(inode);
return inode;
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 444be5c7a1d5..26d2705950a5 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -107,6 +107,13 @@ const struct xattr_handler *ext4_xattr_handlers[] = {
#define EXT4_GET_MB_CACHE(inode) (((struct ext4_sb_info *) \
inode->i_sb->s_fs_info)->s_mb_cache)
+#ifdef CONFIG_LOCKDEP
+void ext4_xattr_inode_set_class(struct inode *ea_inode)
+{
+ lockdep_set_subclass(&ea_inode->i_rwsem, 1);
+}
+#endif
+
static __le32 ext4_xattr_block_csum(struct inode *inode,
sector_t block_nr,
struct ext4_xattr_header *hdr)
@@ -830,6 +837,7 @@ static struct inode *ext4_xattr_inode_create(handle_t *handle,
ea_inode->i_op = &ext4_file_inode_operations;
ea_inode->i_fop = &ext4_file_operations;
ext4_set_aops(ea_inode);
+ ext4_xattr_inode_set_class(ea_inode);
ea_inode->i_generation = inode->i_generation;
EXT4_I(ea_inode)->i_flags |= EXT4_EA_INODE_FL;
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index 6e10ff9393d4..e8bef79bdc38 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -196,3 +196,9 @@ static inline int ext4_init_security(handle_t *handle, struct inode *inode,
return 0;
}
#endif
+
+#ifdef CONFIG_LOCKDEP
+extern void ext4_xattr_inode_set_class(struct inode *ea_inode);
+#else
+static inline void ext4_xattr_inode_set_class(struct inode *ea_inode) { }
+#endif
--
2.13.1.611.g7e3b11ae1-goog
