On Sat 17-02-24 15:41:43, Baokun Li wrote:
On 2024/2/14 0:58, Jan Kara wrote:
On Fri 26-01-24 16:57:13, Baokun Li wrote:
We can easily trigger a BUG_ON by using the following commands:
mount /dev/$disk /tmp/test echo 2147483650 > /sys/fs/ext4/$disk/mb_group_prealloc echo test > /tmp/test/file && sync================================================================== kernel BUG at fs/ext4/mballoc.c:2029! invalid opcode: 0000 [#1] PREEMPT SMP PTI CPU: 3 PID: 320 Comm: kworker/u36:1 Not tainted 6.8.0-rc1 #462 RIP: 0010:mb_mark_used+0x358/0x370 [...] Call Trace: ext4_mb_use_best_found+0x56/0x140 ext4_mb_complex_scan_group+0x196/0x2f0 ext4_mb_regular_allocator+0xa92/0xf00 ext4_mb_new_blocks+0x302/0xbc0 ext4_ext_map_blocks+0x95a/0xef0 ext4_map_blocks+0x2b1/0x680 ext4_do_writepages+0x733/0xbd0 [...] ==================================================================
In ext4_mb_normalize_group_request(): ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
Here fe_len is of type int, but s_mb_group_prealloc is of type unsigned int, so setting s_mb_group_prealloc to 2147483650 overflows fe_len to a negative number, which ultimately triggers a BUG_ON() in mb_mark_used().
Therefore, we add attr_pointer_pi (aka positive int attr pointer) with a value range of 0-INT_MAX to avoid the above problem. In addition to the mb_group_prealloc sysfs interface, the following interfaces also have uint to int conversions that result in overflows, and are also fixed.
err_ratelimit_burst msg_ratelimit_burst warning_ratelimit_burst err_ratelimit_interval_ms msg_ratelimit_interval_ms warning_ratelimit_interval_ms mb_best_avail_max_trim_order
CC: stable@vger.kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com
I don't think you need to change s_mb_group_prealloc here and then restrict it even further in the next patch. I'd just leave it alone here.
Yes, we could put the next patch before this one, but using s_mb_group_prealloc as an example makes it easier to understand why the attr_pointer_pi case is added here.There are several other variables that don't have more convincing examples.
Yes, I think reordering would be good. Because I've read the convertion and started wondering: "is this enough?"
Also I think that limiting mb_best_avail_max_trim_order to 64 instead of INT_MAX will make us more resilient to surprises in the future :) But I don't really insist.
HonzaI think it's enough here to make sure that mb_best_avail_max_trim_order is a positive number, since we always make sure that min_order is not less than 0, as follows:
order = fls(ac->ac_g_ex.fe_len) - 1; min_order = order - sbi->s_mb_best_avail_max_trim_order; if (min_order < 0) min_order = 0;
An oversized mb_best_avail_max_trim_order can be interpreted as always being CR_ANY_FREE. 😄
Well, s_mb_best_avail_max_trim_order is not about allocation passes but about how many times are we willing to shorten the goal extent to half and still use the advanced free blocks search. And I agree that the mballoc code is careful enough that large numbers don't matter there but still why allowing storing garbage values? It is nicer to tell sysadmin he did something wrong right away.
Honza