xfs: get rid of assert from xfs_btree_islastblock

mainline inclusion
from mainline-v6.1-rc4
commit 8c25febf
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8c25febf23963431686f04874b96321288504127

--------------------------------

xfs_btree_check_block contains debugging knobs. With XFS_DEBUG setting up,
turn on the debugging knob can trigger the assert of xfs_btree_islastblock,
test script as follows:

while true
do
    mount $disk $mountpoint
    fsstress -d $testdir -l 0 -n 10000 -p 4 >/dev/null
    echo 1 > /sys/fs/xfs/sda/errortag/btree_chk_sblk
    sleep 10
    umount $mountpoint
done

Kick off fsstress and only *then* turn on the debugging knob. If it
happens that the knob gets turned on after the cntbt lookup succeeds
but before the call to xfs_btree_islastblock, then we *can* end up in
the situation where a previously checked btree block suddenly starts
returning EFSCORRUPTED from xfs_btree_check_block. Kaboom.

Darrick give a very detailed explanation as follows:
Looking back at commit 27d9ee57, I think the point of all this was
to make sure that the cursor has actually performed a lookup, and that
the btree block at whatever level we're asking about is ok.

If the caller hasn't ever done a lookup, the bc_levels array will be
empty, so cur->bc_levels[level].bp pointer will be NULL.  The call to
xfs_btree_get_block will crash anyway, so the "ASSERT(block);" part is
pointless.

If the caller did a lookup but the lookup failed due to block
corruption, the corresponding cur->bc_levels[level].bp pointer will also
be NULL, and we'll still crash.  The "ASSERT(xfs_btree_check_block);"
logic is also unnecessary.

If the cursor level points to an inode root, the block buffer will be
incore, so it had better always be consistent.

If the caller ignores a failed lookup after a successful one and calls
this function, the cursor state is garbage and the assert wouldn't have
tripped anyway. So get rid of the assert.

Fixes: 27d9ee57 ("xfs: actually check xfs_btree_check_block return in xfs_btree_islastblock")
Signed-off-by: NGuo Xuenan <guoxuenan@huawei.com>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NGuo Xuenan <guoxuenan@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/xfs/libxfs/xfs_btree.h

@@ -523,7 +523,6 @@ xfs_btree_islastblock(
 	struct xfs_buf		*bp;
 
 	block = xfs_btree_get_block(cur, level, &bp);
-	ASSERT(block && xfs_btree_check_block(cur, block, level, bp) == 0);
 
 	if (cur->bc_flags & XFS_BTREE_LONG_PTRS)
 		return block->bb_u.l.bb_rightsib == cpu_to_be64(NULLFSBLOCK);