From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 DB86C2F28F0; Fri, 21 Nov 2025 13:34:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763732100; cv=none; b=bcHdi4saQFHGH12FzmBTZbst3Pl4nA2j4GrtkqugyKR7BYJK1agUFkfgiA+22d+bFVkEN/641/9Xm6JnUiUC4t7QXxiJCw0coGtJccXHAfVm5VQEzHbRPtQmfKqs0Fpi6/9LBCVbR6aDl+yJOUuRBya24IuVgppZ+SYytQpjocY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763732100; c=relaxed/simple; bh=L9IXDYPWHesGW+axhlLGBYd3WwEVz1VZaW6MTUOOMZk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=s0qeaKigVm7M44roa9w9Crqdcjp9G3rvPNmBrpxWGoFBX0y+bM0iklqPAs0YWNPfmg1ZbQZh6bOFwIwnbgGacFZheqVtgXkzjSiKko3dB5QS0O5m1kkDNrJV9jDb9XZ0KdlfnljGu+sJXk7qPlg4HygyCPrsTYQITbvqMkk8JO4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AuCzBQR7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="AuCzBQR7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68062C4CEF1; Fri, 21 Nov 2025 13:34:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1763732099; bh=L9IXDYPWHesGW+axhlLGBYd3WwEVz1VZaW6MTUOOMZk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AuCzBQR7xps4DRcVEpXFFQAeAU2RzwNf9W3SjMAJBl8x7tmsscCb5+isSmZqua971 2TycLBFQQvvUWZDhARzZ7NE4ZRTGwbbg8PCYUphpMaYV8NBi6vC3M8NPqodkNHaPuD axDvL+LoXwbI+LHoTZww4pRaKS5Z3DEBDsjOwHpU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Michal Hocko , Vlastimil Babka , Dennis Zhou , Filipe David Manana , Tejun Heo , Andrew Morton , chenxin Subject: [PATCH 6.12 162/185] mm, percpu: do not consider sleepable allocations atomic Date: Fri, 21 Nov 2025 14:13:09 +0100 Message-ID: <20251121130149.722347430@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251121130143.857798067@linuxfoundation.org> References: <20251121130143.857798067@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Hocko [ Upstream commit 9a5b183941b52f84c0f9e5f27ce44e99318c9e0f ] 28307d938fb2 ("percpu: make pcpu_alloc() aware of current gfp context") has fixed a reclaim recursion for scoped GFP_NOFS context. It has done that by avoiding taking pcpu_alloc_mutex. This is a correct solution as the worker context with full GFP_KERNEL allocation/reclaim power and which is using the same lock cannot block the NOFS pcpu_alloc caller. On the other hand this is a very conservative approach that could lead to failures because pcpu_alloc lockless implementation is quite limited. We have a bug report about premature failures when scsi array of 193 devices is scanned. Sometimes (not consistently) the scanning aborts because the iscsid daemon fails to create the queue for a random scsi device during the scan. iscsid itself is running with PR_SET_IO_FLUSHER set so all allocations from this process context are GFP_NOIO. This in turn makes any pcpu_alloc lockless (without pcpu_alloc_mutex) which leads to pre-mature failures. It has turned out that iscsid has worked around this by dropping PR_SET_IO_FLUSHER (https://github.com/open-iscsi/open-iscsi/pull/382) when scanning host. But we can do better in this case on the kernel side and use pcpu_alloc_mutex for NOIO resp. NOFS constrained allocation scopes too. We just need the WQ worker to never trigger IO/FS reclaim. Achieve that by enforcing scoped GFP_NOIO for the whole execution of pcpu_balance_workfn (this will imply NOFS constrain as well). This will remove the dependency chain and preserve the full allocation power of the pcpu_alloc call. While at it make is_atomic really test for blockable allocations. Link: https://lkml.kernel.org/r/20250206122633.167896-1-mhocko@kernel.org Fixes: 28307d938fb2 ("percpu: make pcpu_alloc() aware of current gfp context") Signed-off-by: Michal Hocko Acked-by: Vlastimil Babka Cc: Dennis Zhou Cc: Filipe David Manana Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: chenxin Signed-off-by: Greg Kroah-Hartman --- mm/percpu.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1758,7 +1758,7 @@ void __percpu *pcpu_alloc_noprof(size_t gfp = current_gfp_context(gfp); /* whitelisted flags that can be passed to the backing allocators */ pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN); - is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL; + is_atomic = !gfpflags_allow_blocking(gfp); do_warn = !(gfp & __GFP_NOWARN); /* @@ -2203,7 +2203,12 @@ static void pcpu_balance_workfn(struct w * to grow other chunks. This then gives pcpu_reclaim_populated() time * to move fully free chunks to the active list to be freed if * appropriate. + * + * Enforce GFP_NOIO allocations because we have pcpu_alloc users + * constrained to GFP_NOIO/NOFS contexts and they could form lock + * dependency through pcpu_alloc_mutex */ + unsigned int flags = memalloc_noio_save(); mutex_lock(&pcpu_alloc_mutex); spin_lock_irq(&pcpu_lock); @@ -2214,6 +2219,7 @@ static void pcpu_balance_workfn(struct w spin_unlock_irq(&pcpu_lock); mutex_unlock(&pcpu_alloc_mutex); + memalloc_noio_restore(flags); } /**