| Message ID | 20221130040237.2434259-1-guoxuenan@huawei.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] xfs: get rid of assert from xfs_btree_islastblock | expand |
On Wed, Nov 30, 2022 at 12:02:37PM +0800, Guo Xuenan wrote: > 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 27d9ee577dcce, 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: 27d9ee577dcc ("xfs: actually check xfs_btree_check_block return in xfs_btree_islastblock") > Signed-off-by: Guo Xuenan <guoxuenan@huawei.com> Seems fine to me, but what does everyone else think? Tentatively, Reviewed-by: Darrick J. Wong <djwong@kernel.org> --D > --- > fs/xfs/libxfs/xfs_btree.h | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h > index eef27858a013..29c4b4ccb909 100644 > --- a/fs/xfs/libxfs/xfs_btree.h > +++ b/fs/xfs/libxfs/xfs_btree.h > @@ -556,7 +556,6 @@ 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); > -- > 2.31.1 >
diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h index eef27858a013..29c4b4ccb909 100644 --- a/fs/xfs/libxfs/xfs_btree.h +++ b/fs/xfs/libxfs/xfs_btree.h @@ -556,7 +556,6 @@ 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);
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 27d9ee577dcce, 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: 27d9ee577dcc ("xfs: actually check xfs_btree_check_block return in xfs_btree_islastblock") Signed-off-by: Guo Xuenan <guoxuenan@huawei.com> --- fs/xfs/libxfs/xfs_btree.h | 1 - 1 file changed, 1 deletion(-)