Re: [resend PATCH] ext4: avoid deadlock on sync-mounted ext2 FS
From: Eric Sandeen <hidden>
Date: 2012-02-10 22:43:24
On 02/10/2012 04:31 AM, Martin Wilck wrote:
I don't want to bother, but could someone have a look at this patch please?
You have to bother, to get attention ;)
Martin 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. I am attaching a small patch here that solves this issue for me. In the sync mounted case, ext4_handle_dirty_metadata() may call sync_dirty_buffer(), which can't be called with buffer lock held. My knowledge of locking in ext4 is insufficient to judge if this patch is correct, but it may serve as starting point for others.
This looks an awful lot like: b2f49033d80c952a0ffc2d5647bc1a0b8a09c1b3 [PATCH] fix deadlock in ext2 from 2006! :) But I'm also eyeballing: 8a2bfdcbfa441d8b0e5cb9c9a7f45f77f80da465 [PATCH] ext[34]: EA block reference count racing fix to be sure it doesn't regress anything there. And I'd really like to know why this only happens on ext2-with-ext4 (ext4 nojournal seems ok... hm, actually, I can't repro it on ext2 either...) Ahah. Ok, makes sense, it has to be mkfs'd with a 128-byte inode, so that selinux xattrs will go into an external block. Now I can reproduce it on ext2. But still not on ext4, with 128-byte-inodes and nojournal. Odd. I'd like to sort that out. The patch also unlocks prior to mb_cache_entry_release(), and I think that might put some of the raciness back? -Eric
quoted hunk ↗ jump to hunk
Signed-off-by: Martin.Wilck@ts.fujitsu.com --- fs/ext4/xattr.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 93a00d8..eb771ea 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c@@ -487,8 +487,10 @@ 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); + unlock_buffer(bh); error = ext4_handle_dirty_metadata(handle, inode, bh); if (IS_SYNC(inode)) ext4_handle_sync(handle);@@ -498,7 +500,6 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode, if (ce) mb_cache_entry_release(ce); } - unlock_buffer(bh); out: ext4_std_error(inode->i_sb, error); return;