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Re: [PATCH] xfs: free the efi AIL entry on log recovery failure

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: free the efi AIL entry on log recovery failure
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Thu, 05 Dec 2013 17:06:52 -0600
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131205223244.GJ29897@dastard>
References: <20131205214054.330817383@xxxxxxx> <20131205223244.GJ29897@dastard>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 12/05/13 16:32, Dave Chinner wrote:
On Thu, Dec 05, 2013 at 03:40:07PM -0600, Mark Tinguely wrote:
If freeing an extent fails during recovery, then the filesystem
will be forced down with the EFI entry still on the AIL. This
will result in hanging the function xfs_ail_push_all_sync().

This patch is similar to the patches that removed the dquot and
inode in commits 32ce90a and dea9609.

Found by mounting an metadata dump that triggers a
XFS_WANT_CORRUPTED_RETURN() on log recovery.

Signed-off-by: Mark Tinguely<tinguely@xxxxxxx>
---
  fs/xfs/xfs_log_recover.c |    5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

Index: b/fs/xfs/xfs_log_recover.c
===================================================================
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -3668,7 +3668,7 @@ xlog_recover_process_efi(
                extp =&(efip->efi_format.efi_extents[i]);
                error = xfs_free_extent(tp, extp->ext_start, extp->ext_len);
                if (error)
-                       goto abort_error;
+                       goto free_abort;
                xfs_trans_log_efd_extent(tp, efdp, extp->ext_start,
                                         extp->ext_len);
        }
@@ -3677,6 +3677,9 @@ xlog_recover_process_efi(
        error = xfs_trans_commit(tp, 0);
        return error;

+free_abort:
+       set_bit(XFS_EFI_RECOVERED,&efip->efi_flags);
+       xfs_efi_release(efip, efip->efi_format.efi_nextents);
  abort_error:
        xfs_trans_cancel(tp, XFS_TRANS_ABORT);
        return error;

Why does a failure of xfs_trans_reserve() in this function
not require the XFS_EFI_RECOVERED bit to be set?

If it does require setting the XFS_EFI_RECOVERED bit (I think it
does), then we unconditionally set that bit in
xlog_recover_process_efi() so it should be pulled up to be the first
thing the function does, not something that is handled in the error
paths. IOWs, we leave this function having guaranteed that we've
pulled the EFI from the AIL on any failure.

or not if we move where we remove the entries from the AIL....


Bigger picture: if we fail to recover this EFI, we abort the AIL
walk across all the EFIs in the AIL. That means all unrecovered EFIs
get left in the AIL and this will result in hanging the function
xfs_ail_push_all_sync().  IOWs, this patch only fixes the case where
we get an error on the last EFI in the AIL during recovery.

Hence a larger fix is needed here - if we fail to recover an EFI, we
need to continue to walk the AIL and set the XFS_EFI_RECOVERED bit
on all the EFIs still in the AIL and release them.

...pretty sure the forced shutdown will happen later and the caller, xlog_recover_process_efis(), is already walking the ail with a xfs_ail_cursor. As you mention, there can be more entries, then xlog_recover_process_efis() could continue to use the cursor to the remove the remaining entries from the AIL on error.

Thanks for the feedback.

--Mark.

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