From ec4cb1aa2b7bae18dd8164f2e9c7c51abcf61280 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 7 Apr 2014 10:54:21 -0400 Subject: [PATCH] ext4: fix jbd2 warning under heavy xattr load When heavily exercising xattr code the assertion that jbd2_journal_dirty_metadata() shouldn't return error was triggered: WARNING: at /srv/autobuild-ceph/gitbuilder.git/build/fs/jbd2/transaction.c:1237 jbd2_journal_dirty_metadata+0x1ba/0x260() CPU: 0 PID: 8877 Comm: ceph-osd Tainted: G W 3.10.0-ceph-00049-g68d04c9 #1 Hardware name: Dell Inc. PowerEdge R410/01V648, BIOS 1.6.3 02/07/2011 ffffffff81a1d3c8 ffff880214469928 ffffffff816311b0 ffff880214469968 ffffffff8103fae0 ffff880214469958 ffff880170a9dc30 ffff8802240fbe80 0000000000000000 ffff88020b366000 ffff8802256e7510 ffff880214469978 Call Trace: [] dump_stack+0x19/0x1b [] warn_slowpath_common+0x70/0xa0 [] warn_slowpath_null+0x1a/0x20 [] jbd2_journal_dirty_metadata+0x1ba/0x260 [] __ext4_handle_dirty_metadata+0xa3/0x140 [] ext4_xattr_release_block+0x103/0x1f0 [] ext4_xattr_block_set+0x1e0/0x910 [] ext4_xattr_set_handle+0x38b/0x4a0 [] ? trace_hardirqs_on+0xd/0x10 [] ext4_xattr_set+0xc2/0x140 [] ext4_xattr_user_set+0x47/0x50 [] generic_setxattr+0x6e/0x90 [] __vfs_setxattr_noperm+0x7b/0x1c0 [] vfs_setxattr+0xc4/0xd0 [] setxattr+0x13e/0x1e0 [] ? __sb_start_write+0xe7/0x1b0 [] ? mnt_want_write_file+0x28/0x60 [] ? fget_light+0x3c/0x130 [] ? mnt_want_write_file+0x28/0x60 [] ? __mnt_want_write+0x58/0x70 [] SyS_fsetxattr+0xbe/0x100 [] system_call_fastpath+0x16/0x1b The reason for the warning is that buffer_head passed into jbd2_journal_dirty_metadata() didn't have journal_head attached. This is caused by the following race of two ext4_xattr_release_block() calls: CPU1 CPU2 ext4_xattr_release_block() ext4_xattr_release_block() lock_buffer(bh); /* False */ if (BHDR(bh)->h_refcount == cpu_to_le32(1)) } else { le32_add_cpu(&BHDR(bh)->h_refcount, -1); unlock_buffer(bh); lock_buffer(bh); /* True */ if (BHDR(bh)->h_refcount == cpu_to_le32(1)) get_bh(bh); ext4_free_blocks() ... jbd2_journal_forget() jbd2_journal_unfile_buffer() -> JH is gone error = ext4_handle_dirty_xattr_block(handle, inode, bh); -> triggers the warning We fix the problem by moving ext4_handle_dirty_xattr_block() under the buffer lock. Sadly this cannot be done in nojournal mode as that function can call sync_dirty_buffer() which would deadlock. Luckily in nojournal mode the race is harmless (we only dirty already freed buffer) and thus for nojournal mode we leave the dirtying outside of the buffer lock. Reported-by: Sage Weil Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" Cc: stable@vger.kernel.org --- fs/ext4/xattr.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 1f5cf5880718..4eec399ec807 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -520,8 +520,8 @@ static void ext4_xattr_update_super_block(handle_t *handle, } /* - * Release the xattr block BH: If the reference count is > 1, decrement - * it; otherwise free the block. + * Release the xattr block BH: If the reference count is > 1, decrement it; + * otherwise free the block. */ static void ext4_xattr_release_block(handle_t *handle, struct inode *inode, @@ -542,16 +542,31 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode, if (ce) mb_cache_entry_free(ce); get_bh(bh); + unlock_buffer(bh); 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); + /* + * Beware of this ugliness: Releasing of xattr block references + * from different inodes can race and so we have to protect + * from a race where someone else frees the block (and releases + * its journal_head) before we are done dirtying the buffer. In + * nojournal mode this race is harmless and we actually cannot + * call ext4_handle_dirty_xattr_block() with locked buffer as + * that function can call sync_dirty_buffer() so for that case + * we handle the dirtying after unlocking the buffer. + */ + if (ext4_handle_valid(handle)) + error = ext4_handle_dirty_xattr_block(handle, inode, + bh); unlock_buffer(bh); - error = ext4_handle_dirty_xattr_block(handle, inode, bh); + if (!ext4_handle_valid(handle)) + error = ext4_handle_dirty_xattr_block(handle, inode, + bh); if (IS_SYNC(inode)) ext4_handle_sync(handle); dquot_free_block(inode, EXT4_C2B(EXT4_SB(inode->i_sb), 1)); -- 2.34.1