ext4: avoid deadlock on sync-mounted FS w/o journal

PATCH Applied Eric Sandeen 2 participants 2 messages Feb 16, 2012 – Feb 21, 2012 ext4 file system

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Eric Sandeen

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2012-02-16 23:41 UTC #0 lore raw

PATCH v2 1/1 ext4: avoid deadlock on sync-mounted FS w/o journal

From: [email protected]

Processes hang forever on a sync-mounted ext2 file system that is mounted with the ext4 module (default in Fedora 16).

I can reproduce this reliably by mounting an ext2 partition with "-o sync" and opening a new file an that partition with vim. vim will hang in "D" state forever. The same happens on ext4 without a journal.

I am attaching a small patch here that solves this issue for me. In the sync mounted case without a journal, ext4_handle_dirty_metadata() may call sync_dirty_buffer(), which can't be called with buffer lock held.

Also move mb_cache_entry_release inside lock to avoid race fixed previously by 8a2bfdcb ext[34]: EA block reference count racing fix Nonte too that ext2 fixed this same problem in 2006 with b2f49033 [PATCH] fix deadlock in ext2

Signed-off-by [email protected]

[[email protected]: move mb_cache_entry_release before unlock, edit commit msg]

Signed-off-by Eric Sandeen <[email protected]>

---

fs/ext4/xattr.c +4 -3

index 93a00d8..4410ae7 100644
@@ -487,18 +487,19 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
 		ext4_free_blocks(handle, inode, bh, 0, 1,
 				 EXT4_FREE_BLOCKS_METADATA |
 				 EXT4_FREE_BLOCKS_FORGET);
+		unlock_buffer(bh);
 	} else {
 		le32_add_cpu(&BHDR(bh)->h_refcount, -1);
+		if (ce)
+			mb_cache_entry_release(ce);
+		unlock_buffer(bh);
 		error = ext4_handle_dirty_metadata(handle, inode, bh);
 		if (IS_SYNC(inode))
 			ext4_handle_sync(handle);
 		dquot_free_block(inode, 1);
 		ea_bdebug(bh, "refcount now=%d; releasing",
 			  le32_to_cpu(BHDR(bh)->h_refcount));
-		if (ce)
-			mb_cache_entry_release(ce);
 	}
-	unlock_buffer(bh);
 out:
 	ext4_std_error(inode->i_sb, error);
 	return;

Ted Ts'o

maintainer Applied

2012-02-21 04:08 UTC #1 lore raw

Quoted 15 lines · Eric Sandeen

From: [email protected]
Processes hang forever on a sync-mounted ext2 file system that is mounted with the ext4 module (default in Fedora 16).
I can reproduce this reliably by mounting an ext2 partition with "-o sync" and opening a new file an that partition with vim. vim will hang in "D" state forever. The same happens on ext4 without a journal.
I am attaching a small patch here that solves this issue for me. In the sync mounted case without a journal, ext4_handle_dirty_metadata() may call sync_dirty_buffer(), which can't be called with buffer lock held.

Quoted 8 lines

Also move mb_cache_entry_release inside lock to avoid race fixed previously by 8a2bfdcb ext[34]: EA block reference count racing fix Nonte too that ext2 fixed this same problem in 2006 with b2f49033 [PATCH] fix deadlock in ext2
Signed-off-by [email protected]
[[email protected]: move mb_cache_entry_release before unlock, edit commit msg]
Signed-off-by Eric Sandeen <[email protected]>

Thanks, applied.

- Ted