On Tue, May 08, 2018 at 01:41:57PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Been hitting AIL ordering assert failures recently, but been unable
> to trace them down because the system immediately hangs up onteh
> spinlock that was held when this assert fires:
>
> XFS: Assertion failed: XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0, file: fs/xfs/xfs_trans_ail.c, line: 52
>
> Move the assertions outside of the spinlock so the corpse can
> be dissected. Thanks to Brian Foster for supplying a clean
> way of doing this.
>
> Signed-Off-By: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> fs/xfs/xfs_trans_ail.c | 43 +++++++++++++++++++++++++++++++-----------
> 1 file changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> index 50611d2bcbc2..41e280ef1483 100644
> --- a/fs/xfs/xfs_trans_ail.c
> +++ b/fs/xfs/xfs_trans_ail.c
> @@ -32,30 +32,51 @@
> #ifdef DEBUG
> /*
> * Check that the list is sorted as it should be.
> + *
> + * Called with the ail lock held, but we don't want to assert fail with it
> + * held otherwise we'll lock everything up and won't be able to debug the
> + * cause. Hence we sample and check the state under the AIL lock and return if
> + * everything is fine, otherwise we drop the lock and run the ASSERT checks.
> + * Asserts may not be fatal, so pick the lock back up and continue onwards.
> */
> STATIC void
> xfs_ail_check(
> - struct xfs_ail *ailp,
> - xfs_log_item_t *lip)
> + struct xfs_ail *ailp,
> + struct xfs_log_item *lip)
> {
> - xfs_log_item_t *prev_lip;
> + struct xfs_log_item *prev_lip;
> + struct xfs_log_item *next_lip;
> + xfs_lsn_t prev_lsn = NULLCOMMITLSN;
> + xfs_lsn_t next_lsn = NULLCOMMITLSN;
> + xfs_lsn_t lsn;
> + bool in_ail;
> +
>
> if (list_empty(&ailp->ail_head))
> return;
>
> /*
> - * Check the next and previous entries are valid.
> + * Sample then check the next and previous entries are valid.
> */
> - ASSERT(test_bit(XFS_LI_IN_AIL, &lip->li_flags));
> - prev_lip = list_entry(lip->li_ail.prev, xfs_log_item_t, li_ail);
> + in_ail = test_bit(XFS_LI_IN_AIL, &lip->li_flags);
> + prev_lip = list_entry(lip->li_ail.prev, struct xfs_log_item, li_ail);
> if (&prev_lip->li_ail != &ailp->ail_head)
> - ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
> -
> - prev_lip = list_entry(lip->li_ail.next, xfs_log_item_t, li_ail);
> - if (&prev_lip->li_ail != &ailp->ail_head)
> - ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);
> + prev_lsn = prev_lip->li_lsn;
> + next_lip = list_entry(lip->li_ail.next, struct xfs_log_item, li_ail);
> + if (&next_lip->li_ail != &ailp->ail_head)
> + next_lsn = next_lip->li_lsn;
> + lsn = lip->li_lsn;
>
> + if (in_ail &&
> + (prev_lsn == NULLCOMMITLSN || XFS_LSN_CMP(prev_lsn, lsn) <= 0) &&
> + (next_lsn == NULLCOMMITLSN || XFS_LSN_CMP(next_lsn, lsn) >= 0))
> + return;
>
> + spin_unlock(&ailp->ail_lock);
> + ASSERT(in_ail);
> + ASSERT(prev_lsn == NULLCOMMITLSN || XFS_LSN_CMP(prev_lsn, lsn) <= 0);
> + ASSERT(next_lsn == NULLCOMMITLSN || XFS_LSN_CMP(next_lsn, lsn) >= 0);
> + spin_lock(&ailp->ail_lock);
> }
> #else /* !DEBUG */
> #define xfs_ail_check(a,l)
> --
> 2.17.0
>
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