Re: [PATCH] mm/slab: reject unsupported kmalloc sizes

[Zi Yan]

On Mon Aug 17, 2026 at 10:59 PM EDT, Alan Stern wrote:
> On Mon, Aug 17, 2026 at 04:40:18PM -0400, Zi Yan wrote:
>> kmalloc is used to allocate physically contiguous memory for kernel
>> allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc uses
>> the page allocator and can only support up to KMALLOC_MAX_SIZE. For request
>> sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a WARN
>> because kmalloc allocates an order greater than MAX_PAGE_ORDER. Systems
>> with panic_on_warn=1 crash because of this WARN. Fix it by rejecting any
>> kmalloc size bigger than KMALLOC_MAX_SIZE.
>> 
>> Fixes: aadb4bc4a1f9 ("SLUB: direct pass through of page size or higher kmalloc requests")
>> Reported-by: syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@xxxxxxxxxx/
>> Tested-by: syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>> ---
>> It fixes a page allocator warning (order > MAX_PAGE_ORDER) when gadgetfs
>> requests excessively large memory from kmalloc. Instead of adding
>> __GFP_NOWARN to suppress the warning, as was done for usbfs[1], change
>> kmalloc to return NULL without a warning for this specific issue.
>> 
>> [1] commit 4f2629ea67e72 ("USB: usbfs: Don't WARN about excessively large memory allocations")
>
> Thanks for doing this.  If you like, I can write a follow-up patch to 
> remove the __GFP_NOWARN added in 4f2629ea67e72, now that it isn't needed 
> any more.

Sure. Once the patch gets an Ack or Rb from a maintainer and Andrew
picks it up, feel free to send a cleanup patch. Thanks.

-- 
Best Regards,
Yan, Zi