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ext4: implement error handling of ext4_mb_new_preallocation()

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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).

[ Patch restructed by tytso to make the flow of control easier to follow. ]

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Alexey Khoroshilov 2013-07-01 08:12:36 -04:00 committed by Theodore Ts'o
parent 6ca792edc1
commit 2c00ef3ee3
1 changed files with 10 additions and 7 deletions
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17
fs/ext4/mballoc.c
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@ -4406,17 +4406,20 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
repeat:
/* allocate space in core */
*errp = ext4_mb_regular_allocator(ac);
if (*errp)
goto discard_and_exit;
/* as we've just preallocated more space than
* user requested originally, 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) {
discard_and_exit:
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);