From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D61838E8CA for ; Wed, 29 Jul 2026 04:13:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785298396; cv=none; b=PY2iyDDjLcam3cyORISemTkuKrR+n9Nx0YxQ8XuadFULX4CmjFmo5Ws9Bic0B1tokiddoR0p3eS0/aOdtr7hKFFG1u61GDkFfG5lewmd3EZhiBK808IEZulONgrBQT8v/WK0NNZ3KaHvwKU/0iu1vl7Y0FRmpsTt/ipI6ab1VOg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785298396; c=relaxed/simple; bh=lPNJrBGr+Xf7UMuGgw7kbDtCv+85sbdeeAkkBQ5wU/U=; h=Date:To:From:Subject:Message-Id; b=B0ORu0XKcpuYDSS+NxexVTQigYjKuOQXq2MoQgiRfPpdYHLlyWdaZwQwiw6HTwICKUWd3EPhzG/ZvAZJMJ0TG1E5FKRIKITLuWKzLUFomwN0jBx4wK6qa1fTZKNhHj2XSr1951C2Oy3k3XZkh2/fPydydI6vVDW8OuD1ddq6kXE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ovwuBUUF; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ovwuBUUF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C65601F000E9; Wed, 29 Jul 2026 04:13:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785298394; bh=vdkwVEv78b+E0CcsdpGnTyYk/T863rPjGkdK4vQ/v3A=; h=Date:To:From:Subject; b=ovwuBUUFWaeTTL9y3ciSDsSPF/Ky4VkBpU4mlSkHLAMWiNyNVa5ETHhB1k67/+ozs OsDpcAFltUeqkGp4jQPLBWfWj2l5ZZCZXW28USWAfF9OlneRkXru4llnH2J3HXw2/h xEzJgEuLtFCCEoxqG4ZAj8LEZqumTsZ0ldgDe3c4= Date: Tue, 28 Jul 2026 21:13:14 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,urezki@gmail.com,tj@kernel.org,shivamkalra98@zohomail.in,pfalcato@suse.de,mhocko@suse.com,dennis@kernel.org,cl@gentwo.org,chengkaitao@kylinos.cn,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-percpu-avoid-io-fs-reclaim-in-backing-allocations.patch removed from -mm tree Message-Id: <20260729041314.C65601F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/percpu: avoid IO/FS reclaim in backing allocations has been removed from the -mm tree. Its filename was mm-percpu-avoid-io-fs-reclaim-in-backing-allocations.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Kaitao Cheng Subject: mm/percpu: avoid IO/FS reclaim in backing allocations Date: Thu, 18 Jun 2026 21:04:14 +0800 Commit 9a5b183941b5 ("mm, percpu: do not consider sleepable allocations atomic") allows sleepable GFP_NOIO and GFP_NOFS percpu allocations to take pcpu_alloc_mutex. This avoids premature allocation failures, but it also makes the mutex visible to callers from constrained IO/FS contexts. Thread A calls pcpu_alloc_noprof() with GFP_KERNEL and takes pcpu_alloc_mutex. Since the internal allocation is not constrained by NOFS, it may enter FS reclaim while still holding pcpu_alloc_mutex, creating a dependency like: pcpu_alloc_mutex -> fs_reclaim -> FS lock At the same time, Thread B may already hold an FS lock and then call pcpu_alloc_noprof() with GFP_NOFS. It will try to acquire pcpu_alloc_mutex and block, creating the reverse dependency: FS lock -> pcpu_alloc_mutex This can still form a potential deadlock cycle. Avoid the dependency by restricting percpu backing allocations to GFP_NOIO. The public allocation still uses the caller's GFP context to decide whether it may block, but the internal memory allocations performed while pcpu_alloc_mutex is held cannot recurse into IO or FS reclaim. Link: https://lore.kernel.org/20260618130414.96383-5-kaitao.cheng@linux.dev Fixes: 9a5b183941b5 ("mm, percpu: do not consider sleepable allocations atomic") Signed-off-by: Kaitao Cheng Cc: Christoph Lameter Cc: Dennis Zhou Cc: Michal Hocko Cc: Pedro Falcato Cc: Shivam Kalra Cc: Tejun Heo Cc: Uladzislau Rezki (Sony) Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/percpu.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) --- a/mm/percpu.c~mm-percpu-avoid-io-fs-reclaim-in-backing-allocations +++ a/mm/percpu.c @@ -1726,9 +1726,8 @@ static void pcpu_alloc_tag_free_hook(str * @gfp: allocation flags * * Allocate percpu area of @size bytes aligned at @align. If @gfp doesn't - * contain %GFP_KERNEL, the allocation is atomic. If @gfp has __GFP_NOWARN - * then no warning will be triggered on invalid or failed allocation - * requests. + * allow blocking, the allocation is atomic. If @gfp has __GFP_NOWARN then no + * warning will be triggered on invalid or failed allocation requests. * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. @@ -1749,8 +1748,17 @@ void __percpu *pcpu_alloc_noprof(size_t size_t bits, bit_align; gfp = current_gfp_context(gfp); - /* whitelisted flags that can be passed to the backing allocators */ - pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN); + /* + * Allowlisted flags that can be passed to the backing allocators. + * Backing allocations under pcpu_alloc_mutex must not recurse into + * IO/FS reclaim. Otherwise a GFP_KERNEL caller holding the mutex can + * block on reclaim while a GFP_NOIO/NOFS caller holding an IO/FS lock + * waits for the same mutex. + * + * Do not pass __GFP_NOFAIL. A small percpu allocation may need many + * backing pages, making nofail reclaim too costly under NOIO/NOFS. + */ + pcpu_gfp = gfp & (GFP_NOIO | __GFP_NORETRY | __GFP_NOWARN); is_atomic = !gfpflags_allow_blocking(gfp); do_warn = !(gfp & __GFP_NOWARN); _ Patches currently in -mm which might be from chengkaitao@kylinos.cn are mm-kconfig-drop-redundant-memory-hotplug-dependencies.patch mm-kconfig-drop-redundant-dependency-wrappers.patch