From: Dave Chinner dchinner@redhat.com
[ Upstream commit 348a1983cf4cf5099fc398438a968443af4c9f65 ]
Luis has been reporting an assert failure when freeing an inode cluster during inode inactivation for a while. The assert looks like:
XFS: Assertion failed: bp->b_flags & XBF_DONE, file: fs/xfs/xfs_trans_buf.c, line: 241 ------------[ cut here ]------------ kernel BUG at fs/xfs/xfs_message.c:102! Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 4 PID: 73 Comm: kworker/4:1 Not tainted 6.10.0-rc1 #4 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: xfs-inodegc/loop5 xfs_inodegc_worker [xfs] RIP: 0010:assfail (fs/xfs/xfs_message.c:102) xfs RSP: 0018:ffff88810188f7f0 EFLAGS: 00010202 RAX: 0000000000000000 RBX: ffff88816e748250 RCX: 1ffffffff844b0e7 RDX: 0000000000000004 RSI: ffff88810188f558 RDI: ffffffffc2431fa0 RBP: 1ffff11020311f01 R08: 0000000042431f9f R09: ffffed1020311e9b R10: ffff88810188f4df R11: ffffffffac725d70 R12: ffff88817a3f4000 R13: ffff88812182f000 R14: ffff88810188f998 R15: ffffffffc2423f80 FS: 0000000000000000(0000) GS:ffff8881c8400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055fe9d0f109c CR3: 000000014426c002 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> xfs_trans_read_buf_map (fs/xfs/xfs_trans_buf.c:241 (discriminator 1)) xfs xfs_imap_to_bp (fs/xfs/xfs_trans.h:210 fs/xfs/libxfs/xfs_inode_buf.c:138) xfs xfs_inode_item_precommit (fs/xfs/xfs_inode_item.c:145) xfs xfs_trans_run_precommits (fs/xfs/xfs_trans.c:931) xfs __xfs_trans_commit (fs/xfs/xfs_trans.c:966) xfs xfs_inactive_ifree (fs/xfs/xfs_inode.c:1811) xfs xfs_inactive (fs/xfs/xfs_inode.c:2013) xfs xfs_inodegc_worker (fs/xfs/xfs_icache.c:1841 fs/xfs/xfs_icache.c:1886) xfs process_one_work (kernel/workqueue.c:3231) worker_thread (kernel/workqueue.c:3306 (discriminator 2) kernel/workqueue.c:3393 (discriminator 2)) kthread (kernel/kthread.c:389) ret_from_fork (arch/x86/kernel/process.c:147) ret_from_fork_asm (arch/x86/entry/entry_64.S:257) </TASK>
And occurs when the the inode precommit handlers is attempt to look up the inode cluster buffer to attach the inode for writeback.
The trail of logic that I can reconstruct is as follows.
1. the inode is clean when inodegc runs, so it is not attached to a cluster buffer when precommit runs.
2. #1 implies the inode cluster buffer may be clean and not pinned by dirty inodes when inodegc runs.
3. #2 implies that the inode cluster buffer can be reclaimed by memory pressure at any time.
4. The assert failure implies that the cluster buffer was attached to the transaction, but not marked done. It had been accessed earlier in the transaction, but not marked done.
5. #4 implies the cluster buffer has been invalidated (i.e. marked stale).
6. #5 implies that the inode cluster buffer was instantiated uninitialised in the transaction in xfs_ifree_cluster(), which only instantiates the buffers to invalidate them and never marks them as done.
Given factors 1-3, this issue is highly dependent on timing and environmental factors. Hence the issue can be very difficult to reproduce in some situations, but highly reliable in others. Luis has an environment where it can be reproduced easily by g/531 but, OTOH, I've reproduced it only once in ~2000 cycles of g/531.
I think the fix is to have xfs_ifree_cluster() set the XBF_DONE flag on the cluster buffers, even though they may not be initialised. The reasons why I think this is safe are:
1. A buffer cache lookup hit on a XBF_STALE buffer will clear the XBF_DONE flag. Hence all future users of the buffer know they have to re-initialise the contents before use and mark it done themselves.
2. xfs_trans_binval() sets the XFS_BLI_STALE flag, which means the buffer remains locked until the journal commit completes and the buffer is unpinned. Hence once marked XBF_STALE/XFS_BLI_STALE by xfs_ifree_cluster(), the only context that can access the freed buffer is the currently running transaction.
3. #2 implies that future buffer lookups in the currently running transaction will hit the transaction match code and not the buffer cache. Hence XBF_STALE and XFS_BLI_STALE will not be cleared unless the transaction initialises and logs the buffer with valid contents again. At which point, the buffer will be marked marked XBF_DONE again, so having XBF_DONE already set on the stale buffer is a moot point.
4. #2 also implies that any concurrent access to that cluster buffer will block waiting on the buffer lock until the inode cluster has been fully freed and is no longer an active inode cluster buffer.
5. #4 + #1 means that any future user of the disk range of that buffer will always see the range of disk blocks covered by the cluster buffer as not done, and hence must initialise the contents themselves.
6. Setting XBF_DONE in xfs_ifree_cluster() then means the unlinked inode precommit code will see a XBF_DONE buffer from the transaction match as it expects. It can then attach the stale but newly dirtied inode to the stale but newly dirtied cluster buffer without unexpected failures. The stale buffer will then sail through the journal and do the right thing with the attached stale inode during unpin.
Hence the fix is just one line of extra code. The explanation of why we have to set XBF_DONE in xfs_ifree_cluster, OTOH, is long and complex....
Fixes: 82842fee6e59 ("xfs: fix AGF vs inode cluster buffer deadlock") Signed-off-by: Dave Chinner dchinner@redhat.com Tested-by: Luis Chamberlain mcgrof@kernel.org Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Chandan Babu R chandanbabu@kernel.org Signed-off-by: Leah Rumancik leah.rumancik@gmail.com Acked-by: Chandan Babu R chandanbabu@kernel.org --- fs/xfs/xfs_inode.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c index 4e73dd4a4d82..8c7cbe7f47ef 100644 --- a/fs/xfs/xfs_inode.c +++ b/fs/xfs/xfs_inode.c @@ -2297,11 +2297,26 @@ xfs_ifree_cluster( * This buffer may not have been correctly initialised as we * didn't read it from disk. That's not important because we are * only using to mark the buffer as stale in the log, and to - * attach stale cached inodes on it. That means it will never be - * dispatched for IO. If it is, we want to know about it, and we - * want it to fail. We can acheive this by adding a write - * verifier to the buffer. + * attach stale cached inodes on it. + * + * For the inode that triggered the cluster freeing, this + * attachment may occur in xfs_inode_item_precommit() after we + * have marked this buffer stale. If this buffer was not in + * memory before xfs_ifree_cluster() started, it will not be + * marked XBF_DONE and this will cause problems later in + * xfs_inode_item_precommit() when we trip over a (stale, !done) + * buffer to attached to the transaction. + * + * Hence we have to mark the buffer as XFS_DONE here. This is + * safe because we are also marking the buffer as XBF_STALE and + * XFS_BLI_STALE. That means it will never be dispatched for + * IO and it won't be unlocked until the cluster freeing has + * been committed to the journal and the buffer unpinned. If it + * is written, we want to know about it, and we want it to + * fail. We can acheive this by adding a write verifier to the + * buffer. */ + bp->b_flags |= XBF_DONE; bp->b_ops = &xfs_inode_buf_ops;
/*