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Subject[PATCH] ext4: implement error handling of ext4_mb_new_preallocation()
Date
If memory allocation in ext4_mb_new_group_pa() is failed,
it returns error code, ext4_mb_new_preallocation() propages it,
but ext4_mb_new_blocks() ignores it.

An observed result was:
- allocation fail means ext4_mb_new_group_pa() does not update ext4_allocation_context;
- ext4_mb_new_blocks() sets ext4_allocation_request->len (ar->len = ac->ac_b_ex.fe_len;)
to number of blocks preallocated (512) instead of number of blocks requested (1);
- that activates update cycle in ext4_splice_branch():
for (i = 1; i < blks; i++) <-- blks is 512 instead of 1 here
*(where->p + i) = cpu_to_le32(current_block++);
- it iterates 511 times and corrupts a chunk of memory including inode structure;
- page fault happens at EXT4_SB(inode->i_sb) in ext4_mark_inode_dirty();
- system hangs with 'scheduling while atomic' BUG.

The patch implements a check for ext4_mb_new_preallocation() error code
and handles its failure as if ext4_mb_regular_allocator() fails.

Found by Linux File System Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
---
fs/ext4/mballoc.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index b1ed9e0..95c6b0d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4401,17 +4401,18 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
repeat:
/* allocate space in core */
*errp = ext4_mb_regular_allocator(ac);
+ if (!*errp) {
+ /* as we've just preallocated more space than
+ * user requested orinally, we store allocated
+ * space in a special descriptor */
+ if (ac->ac_status == AC_STATUS_FOUND &&
+ ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
+ *errp = ext4_mb_new_preallocation(ac);
+ }
if (*errp) {
ext4_discard_allocated_blocks(ac);
goto errout;
}
-
- /* as we've just preallocated more space than
- * user requested orinally, we store allocated
- * space in a special descriptor */
- if (ac->ac_status == AC_STATUS_FOUND &&
- ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
- ext4_mb_new_preallocation(ac);
}
if (likely(ac->ac_status == AC_STATUS_FOUND)) {
*errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
--
1.7.9.5


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