linux-kernel - Re: [PATCH] slab: prevent infinite loop in kmalloc

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Message-ID: <CAADnVQ+pMfza=PF6eo05gSrtGkE1LbT6Fsg6DnmqZcta-3KUiQ@mail.gmail.com>
Date: Mon, 3 Nov 2025 10:49:20 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Harry Yoo <harry.yoo@...cle.com>, Alexei Starovoitov <ast@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slab: prevent infinite loop in kmalloc_nolock() with debugging

On Mon, Nov 3, 2025 at 4:24 AM Vlastimil Babka <vbabka@...e.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@...cle.com>
> Closes: https://lore.kernel.org/all/aQLqZjjq1SPD3Fml@hyeyoo/
> Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> as we discussed in the linked thread, 6.18 hotfix to be included in
> slab/for-next-fixes

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