Commit bc36dfff authored Feb 24, 2020 by Jan Kara

ext2: Silence lockdep warning about reclaim under xattr_sem



Lockdep complains about a chain:
  sb_internal#2 --> &ei->xattr_sem#2 --> fs_reclaim

and shrink_dentry_list -> ext2_evict_inode -> ext2_xattr_delete_inode ->
down_write(ei->xattr_sem) creating a locking cycle in the reclaim path.
This is however a false positive because when we are in
ext2_evict_inode() we are the only holder of the inode reference and
nobody else should touch xattr_sem of that inode. So we cannot ever
block on acquiring the xattr_sem in the reclaim path.

Silence the lockdep warning by using down_write_trylock() in
ext2_xattr_delete_inode() to not create false locking dependency.

Reported-by: "J. R. Okajima" <hooanon05g@gmail.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Jan Kara <jack@suse.cz>

parent f8788d86

fs/ext2/xattr.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -790,7 +790,15 @@ ext2_xattr_delete_inode(struct inode *inode)
		struct buffer_head *bh = NULL;
		struct ext2_sb_info *sbi = EXT2_SB(inode->i_sb);

		down_write(&EXT2_I(inode)->xattr_sem);
		/*
		* We are the only ones holding inode reference. The xattr_sem should
		* better be unlocked! We could as well just not acquire xattr_sem at
		* all but this makes the code more futureproof. OTOH we need trylock
		* here to avoid false-positive warning from lockdep about reclaim
		* circular dependency.
		*/
		if (WARN_ON_ONCE(!down_write_trylock(&EXT2_I(inode)->xattr_sem)))
		return;
		if (!EXT2_I(inode)->i_file_acl)
		goto cleanup;

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