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xfs: set buffer ops when repair probes for btree type

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In xrep_findroot_block, we work out the btree type and correctness of a
given block by calling different btree verifiers on root block
candidates.  However, we leave the NULL b_ops while ->verify_read
validates the block, which means that if the verifier calls
xfs_buf_verifier_error it'll crash on the null b_ops.  Fix it to set
b_ops before calling the verifier and unsetting it if the verifier
fails.

Furthermore, improve the documentation around xfs_buf_ensure_ops, which
is the function that is responsible for cleaning up the b_ops state of
buffers that go through xrep_findroot_block but don't match anything.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
This commit is contained in:
Darrick J. Wong 2019-02-03 14:03:59 -08:00
parent 465fa17f4a
commit add46b3b02
2 changed files with 24 additions and 3 deletions
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11
fs/xfs/scrub/repair.c
View File

@ -768,18 +768,23 @@ xrep_findroot_block(
if (!uuid_equal(&btblock->bb_u.s.bb_uuid,
&mp->m_sb.sb_meta_uuid))
goto out;
/*
* Read verifiers can reference b_ops, so we set the pointer
* here. If the verifier fails we'll reset the buffer state
* to what it was before we touched the buffer.
*/
bp->b_ops = fab->buf_ops;
fab->buf_ops->verify_read(bp);
if (bp->b_error) {
bp->b_ops = NULL;
bp->b_error = 0;
goto out;
}
/*
* Some read verifiers will (re)set b_ops, so we must be
* careful not to blow away any such assignment.
* careful not to change b_ops after running the verifier.
*/
if (!bp->b_ops)
bp->b_ops = fab->buf_ops;
}
/*

16
fs/xfs/xfs_buf.c
View File

@ -776,10 +776,26 @@ _xfs_buf_read(
}
/*
* Set buffer ops on an unchecked buffer and validate it, if possible.
*
* If the caller passed in an ops structure and the buffer doesn't have ops
* assigned, set the ops and use them to verify the contents. If the contents
* cannot be verified, we'll clear XBF_DONE. We assume the buffer has no
* recorded errors and is already in XBF_DONE state.
*
* Under normal operations, every in-core buffer must have buffer ops assigned
* to them when the buffer is read in from disk so that we can validate the
* metadata.
*
* However, there are two scenarios where one can encounter in-core buffers
* that don't have buffer ops. The first is during log recovery of buffers on
* a V4 filesystem, though these buffers are purged at the end of recovery.
*
* The other is online repair, which tries to match arbitrary metadata blocks
* with btree types in order to find the root. If online repair doesn't match
* the buffer with /any/ btree type, the buffer remains in memory in DONE state
* with no ops, and a subsequent read_buf call from elsewhere will not set the
* ops. This function helps us fix this situation.
*/
int
xfs_buf_ensure_ops(