This is a note to let you know that I've just added the patch titled
ext4: prevent the normalized size from exceeding EXT_MAX_BLOCKS
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ext4-prevent-the-normalized-size-from-exceeding-ext_max_blocks.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2dcf5fde6dffb312a4bfb8ef940cea2d1f402e32 Mon Sep 17 00:00:00 2001
From: Baokun Li <libaokun1@xxxxxxxxxx>
Date: Mon, 27 Nov 2023 14:33:13 +0800
Subject: ext4: prevent the normalized size from exceeding EXT_MAX_BLOCKS
From: Baokun Li <libaokun1@xxxxxxxxxx>
commit 2dcf5fde6dffb312a4bfb8ef940cea2d1f402e32 upstream.
For files with logical blocks close to EXT_MAX_BLOCKS, the file size
predicted in ext4_mb_normalize_request() may exceed EXT_MAX_BLOCKS.
This can cause some blocks to be preallocated that will not be used.
And after [Fixes], the following issue may be triggered:
=========================================================
kernel BUG at fs/ext4/mballoc.c:4653!
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
CPU: 1 PID: 2357 Comm: xfs_io 6.7.0-rc2-00195-g0f5cc96c367f
Hardware name: linux,dummy-virt (DT)
pc : ext4_mb_use_inode_pa+0x148/0x208
lr : ext4_mb_use_inode_pa+0x98/0x208
Call trace:
ext4_mb_use_inode_pa+0x148/0x208
ext4_mb_new_inode_pa+0x240/0x4a8
ext4_mb_use_best_found+0x1d4/0x208
ext4_mb_try_best_found+0xc8/0x110
ext4_mb_regular_allocator+0x11c/0xf48
ext4_mb_new_blocks+0x790/0xaa8
ext4_ext_map_blocks+0x7cc/0xd20
ext4_map_blocks+0x170/0x600
ext4_iomap_begin+0x1c0/0x348
=========================================================
Here is a calculation when adjusting ac_b_ex in ext4_mb_new_inode_pa():
ex.fe_logical = orig_goal_end - EXT4_C2B(sbi, ex.fe_len);
if (ac->ac_o_ex.fe_logical >= ex.fe_logical)
goto adjust_bex;
The problem is that when orig_goal_end is subtracted from ac_b_ex.fe_len
it is still greater than EXT_MAX_BLOCKS, which causes ex.fe_logical to
overflow to a very small value, which ultimately triggers a BUG_ON in
ext4_mb_new_inode_pa() because pa->pa_free < len.
The last logical block of an actual write request does not exceed
EXT_MAX_BLOCKS, so in ext4_mb_normalize_request() also avoids normalizing
the last logical block to exceed EXT_MAX_BLOCKS to avoid the above issue.
The test case in [Link] can reproduce the above issue with 64k block size.
Link: https://patchwork.kernel.org/project/fstests/list/?series=804003
Cc: <stable@xxxxxxxxxx> # 6.4
Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/20231127063313.3734294-1-libaokun1@xxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/ext4/mballoc.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3207,6 +3207,10 @@ ext4_mb_normalize_request(struct ext4_al
start = max(start, rounddown(ac->ac_o_ex.fe_logical,
(ext4_lblk_t)EXT4_BLOCKS_PER_GROUP(ac->ac_sb)));
+ /* avoid unnecessary preallocation that may trigger assertions */
+ if (start + size > EXT_MAX_BLOCKS)
+ size = EXT_MAX_BLOCKS - start;
+
/* don't cover already allocated blocks in selected range */
if (ar->pleft && start <= ar->lleft) {
size -= ar->lleft + 1 - start;
Patches currently in stable-queue which might be from libaokun1@xxxxxxxxxx are
queue-4.14/ext4-prevent-the-normalized-size-from-exceeding-ext_max_blocks.patch
