Re: [PATCH] slab: prevent infinite loop in kmalloc_nolock() with debugging

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Nov 3, 2025 at 4:24 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> In review of a followup work, Harry noticed a potential infinite loop.
> Upon closed inspection, it already exists for kmalloc_nolock() on a
> cache with debugging enabled, since commit af92793e52c3 ("slab:
> Introduce kmalloc_nolock() and kfree_nolock().")
>
> When alloc_single_from_new_slab() fails to trylock node list_lock, we
> keep retrying to get partial slab or allocate a new slab. If we indeed
> interrupted somebody holding the list_lock, the trylock fill fail
> deterministically and we end up allocating and defer-freeing slabs
> indefinitely with no progress.
>
> To fix it, fail the allocation if spinning is not allowed. This is
> acceptable in the restricted context of kmalloc_nolock(), especially
> with debugging enabled.
>
> Reported-by: Harry Yoo <harry.yoo@oracle.com>
> Closes: https://lore.kernel.org/all/aQLqZjjq1SPD3Fml@hyeyoo/
> Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> as we discussed in the linked thread, 6.18 hotfix to be included in
> slab/for-next-fixes

Acked-by: Alexei Starovoitov <ast@kernel.org>