From: Theodore Ts'o Subject: Re: [PATCH] ext4: implement error handling of ext4_mb_new_preallocation() Date: Mon, 17 Jun 2013 09:17:37 -0400 Message-ID: <20130617131737.GA22317@thunk.org> References: <1367787075-11626-1-git-send-email-khoroshilov@ispras.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, spruce-project@linuxtesting.org To: Alexey Khoroshilov Return-path: Content-Disposition: inline In-Reply-To: <1367787075-11626-1-git-send-email-khoroshilov@ispras.ru> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Mon, May 06, 2013 at 12:51:15AM +0400, Alexey Khoroshilov wrote: > 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 Hi Alexey, Thanks for reporting this bug, and proposing a fix. I've restructured the patch slightly to make the flow of control slightly easier to follow, and more consistent with the coding style in ext4. Thanks again! - Ted >From fa4f073ab981d4aabb61f9262405af53072a0d8d Mon Sep 17 00:00:00 2001 From: Alexey Khoroshilov Date: Mon, 17 Jun 2013 09:15:34 -0400 Subject: [PATCH] ext4: implement error handling of ext4_mb_new_preallocation() 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 Signed-off-by: "Theodore Ts'o" --- fs/ext4/mballoc.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 1a9c22b..a9ff5e5 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -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) { - ext4_discard_allocated_blocks(ac); - goto errout; - } + if (*errp) + goto discard_and_exit; /* as we've just preallocated more space than - * user requested orinally, we store allocated + * 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) - ext4_mb_new_preallocation(ac); + 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; + } } if (likely(ac->ac_status == AC_STATUS_FOUND)) { *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs); -- 1.7.12.rc0.22.gcdd159b