Re: [syzbot] [mm?] WARNING in xfs_init_fs_context

[Tetsuo Handa]

On 2025/07/08 17:50, Vlastimil Babka wrote:
> On 7/8/25 00:10, Dave Chinner wrote:
>> On Wed, Jul 02, 2025 at 09:30:30AM +0200, Vlastimil Babka wrote:
>>> On 7/2/25 3:41 AM, Tetsuo Handa wrote:
>>>> By the way, why is xfs_init_fs_context() using __GFP_NOFAIL ?
>>>>
>>>> 	mp = kzalloc(sizeof(struct xfs_mount), GFP_KERNEL | __GFP_NOFAIL);
>>>> 	if (!mp)
>>>> 		return -ENOMEM;
>>>>
>>>> This looks an allocation attempt which can fail safely.
>>
>> It's irrelevant - it shouldn't fail regardless of __GFP_NOFAIL being
>> specified.
> 
> If you mean the "too small to fail" behavior then it's generally true,
> except in some corner cases like being an oom victim, in which case the
> allocation can fail - the userspace process is doomed anyway. But a (small)
> kernel allocation not handling NULL would still need __GFP_NOFAIL to prevent
> that corner case.

init_fs_context() is allowed to fail.

https://elixir.bootlin.com/linux/v6.16-rc4/source/fs/fs_context.c#L318
https://elixir.bootlin.com/linux/v6.16-rc4/source/fs/ext4/super.c#L1990

Therefore, I wonder why xfs does not want xfs_init_fs_context() to fail
with -ENOMEM.