xfs: empty xattr leaf header blocks are not corruption
TLDR: Revert commit 51e6104f ("xfs: detect empty attr leaf blocks in xfs_attr3_leaf_verify") because it was wrong. Every now and then we get a corruption report from the kernel or xfs_repair about empty leaf blocks in the extended attribute structure. We've long thought that these shouldn't be possible, but prior to 5.18 one would shake loose in the recoveryloop fstests about once a month. A new addition to the xattr leaf block verifier in 5.19-rc1 makes this happen every 7 minutes on my testing cloud. I added a ton of logging to detect any time we set the header count on an xattr leaf block to zero. This produced the following dmesg output on generic/388: XFS (sda4): ino 0x21fcbaf leaf 0x129bf78 hdcount==0! Call Trace: <TASK> dump_stack_lvl+0x34/0x44 xfs_attr3_leaf_create+0x187/0x230 xfs_attr_shortform_to_leaf+0xd1/0x2f0 xfs_attr_set_iter+0x73e/0xa90 xfs_xattri_finish_update+0x45/0x80 xfs_attr_finish_item+0x1b/0xd0 xfs_defer_finish_noroll+0x19c/0x770 __xfs_trans_commit+0x153/0x3e0 xfs_attr_set+0x36b/0x740 xfs_xattr_set+0x89/0xd0 __vfs_setxattr+0x67/0x80 __vfs_setxattr_noperm+0x6e/0x120 vfs_setxattr+0x97/0x180 setxattr+0x88/0xa0 path_setxattr+0xc3/0xe0 __x64_sys_setxattr+0x27/0x30 do_syscall_64+0x35/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0 So now we know that someone is creating empty xattr leaf blocks as part of converting a sf xattr structure into a leaf xattr structure. The conversion routine logs any existing sf attributes in the same transaction that creates the leaf block, so we know this is a setxattr to a file that has no attributes at all. Next, g/388 calls the shutdown ioctl and cycles the mount to trigger log recovery. I also augmented buffer item recovery to call ->verify_struct on any attr leaf blocks and complain if it finds a failure: XFS (sda4): Unmounting Filesystem XFS (sda4): Mounting V5 Filesystem XFS (sda4): Starting recovery (logdev: internal) XFS (sda4): xattr leaf daddr 0x129bf78 hdrcount == 0! Call Trace: <TASK> dump_stack_lvl+0x34/0x44 xfs_attr3_leaf_verify+0x3b8/0x420 xlog_recover_buf_commit_pass2+0x60a/0x6c0 xlog_recover_items_pass2+0x4e/0xc0 xlog_recover_commit_trans+0x33c/0x350 xlog_recovery_process_trans+0xa5/0xe0 xlog_recover_process_data+0x8d/0x140 xlog_do_recovery_pass+0x19b/0x720 xlog_do_log_recovery+0x62/0xc0 xlog_do_recover+0x33/0x1d0 xlog_recover+0xda/0x190 xfs_log_mount+0x14c/0x360 xfs_mountfs+0x517/0xa60 xfs_fs_fill_super+0x6bc/0x950 get_tree_bdev+0x175/0x280 vfs_get_tree+0x1a/0x80 path_mount+0x6f5/0xaa0 __x64_sys_mount+0x103/0x140 do_syscall_64+0x35/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0 RIP: 0033:0x7fc61e241eae And a moment later, the _delwri_submit of the recovered buffers trips the same verifier and recovery fails: XFS (sda4): Metadata corruption detected at xfs_attr3_leaf_verify+0x393/0x420 [xfs], xfs_attr3_leaf block 0x129bf78 XFS (sda4): Unmount and run xfs_repair XFS (sda4): First 128 bytes of corrupted metadata buffer: 00000000: 00 00 00 00 00 00 00 00 3b ee 00 00 00 00 00 00 ........;....... 00000010: 00 00 00 00 01 29 bf 78 00 00 00 00 00 00 00 00 .....).x........ 00000020: a5 1b d0 02 b2 9a 49 df 8e 9c fb 8d f8 31 3e 9d ......I......1>. 00000030: 00 00 00 00 02 1f cb af 00 00 00 00 10 00 00 00 ................ 00000040: 00 50 0f b0 00 00 00 00 00 00 00 00 00 00 00 00 .P.............. 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ XFS (sda4): Corruption of in-memory data (0x8) detected at _xfs_buf_ioapply+0x37f/0x3b0 [xfs] (fs/xfs/xfs_buf.c:1518). Shutting down filesystem. XFS (sda4): Please unmount the filesystem and rectify the problem(s) XFS (sda4): log mount/recovery failed: error -117 XFS (sda4): log mount failed I think I see what's going on here -- setxattr is racing with something that shuts down the filesystem: Thread 1 Thread 2 -------- -------- xfs_attr_sf_addname xfs_attr_shortform_to_leaf <create empty leaf> xfs_trans_bhold(leaf) xattri_dela_state = XFS_DAS_LEAF_ADD <roll transaction> <flush log> <shut down filesystem> xfs_trans_bhold_release(leaf) <discover fs is dead, bail> Thread 3 -------- <cycle mount, start recovery> xlog_recover_buf_commit_pass2 xlog_recover_do_reg_buffer <replay empty leaf buffer from recovered buf item> xfs_buf_delwri_queue(leaf) xfs_buf_delwri_submit _xfs_buf_ioapply(leaf) xfs_attr3_leaf_write_verify <trip over empty leaf buffer> <fail recovery> As you can see, the bhold keeps the leaf buffer locked and thus prevents the *AIL* from tripping over the ichdr.count==0 check in the write verifier. Unfortunately, it doesn't prevent the log from getting flushed to disk, which sets up log recovery to fail. So. It's clear that the kernel has always had the ability to persist attr leaf blocks with ichdr.count==0, which means that it's part of the ondisk format now. Unfortunately, this check has been added and removed multiple times throughout history. It first appeared in[1] kernel 3.10 as part of the early V5 format patches. The check was later discovered to break log recovery and hence disabled[2] during log recovery in kernel 4.10. Simultaneously, the check was added[3] to xfs_repair 4.9.0 to try to weed out the empty leaf blocks. This was still not correct because log recovery would recover an empty attr leaf block successfully only for regular xattr operations to trip over the empty block during of the block during regular operation. Therefore, the check was removed entirely[4] in kernel 5.7 but removal of the xfs_repair check was forgotten. The continued complaints from xfs_repair lead to us mistakenly re-adding[5] the verifier check for kernel 5.19. Remove it once again. [1] 517c2220 ("xfs: add CRCs to attr leaf blocks") [2] 2e1d2337 ("xfs: ignore leaf attr ichdr.count in verifier during log replay") [3] f7140161 ("xfs_repair: junk leaf attribute if count == 0") [4] f28cef9e ("xfs: don't fail verifier on empty attr3 leaf block") [5] 51e6104f ("xfs: detect empty attr leaf blocks in xfs_attr3_leaf_verify") Looking at the rest of the xattr code, it seems that files with empty leaf blocks behave as expected -- listxattr reports no attributes; getxattr on any xattr returns nothing as expected; removexattr does nothing; and setxattr can add attributes just fine. Original-bug: 517c2220 ("xfs: add CRCs to attr leaf blocks") Still-not-fixed-by: 2e1d2337 ("xfs: ignore leaf attr ichdr.count in verifier during log replay") Removed-in: f28cef9e ("xfs: don't fail verifier on empty attr3 leaf block") Fixes: 51e6104f ("xfs: detect empty attr leaf blocks in xfs_attr3_leaf_verify") Signed-off-by:Darrick J. Wong <djwong@kernel.org> Reviewed-by:
Dave Chinner <dchinner@redhat.com>
Showing
Please register or sign in to comment