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client-ip=58.252.5.68; helo=mail.oppo.com; pr=C Received: from mail.oppo.com (58.252.5.68) by SG1PEPF000082E1.mail.protection.outlook.com (10.167.240.4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.7544.18 via Frontend Transport; Thu, 9 May 2024 01:31:01 +0000 Received: from oppo.com (172.16.40.118) by mailappw31.adc.com (172.16.56.198) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Thu, 9 May 2024 09:31:00 +0800 Date: Thu, 9 May 2024 09:30:59 +0800 From: Hailong Liu To: Gao Xiang CC: , Michal Hocko , , , , <21cnbao@gmail.com>, , , , , Oven Subject: Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL Message-ID: <20240509013059.vegko7dlty7vppy5@oppo.com> References: <20240508125808.28882-1-hailong.liu@oppo.com> <404add29-2d3f-45db-9103-0c5b66fb254e@linux.alibaba.com> <20240508144321.ymnhn54daaabalhe@oppo.com> <90a127e5-d884-44b5-bb76-773a7485c2f1@linux.alibaba.com> <20240508153136.x4rxildsgza234uv@oppo.com> <52f9e300-4ab9-43c1-abae-cbe3da27e5b0@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; 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May 23:40, Gao Xiang wrote: > > > On 2024/5/8 23:31, Hailong Liu wrote: > > On Wed, 08. May 23:10, Gao Xiang wrote: > > > Hi, > > > > > > On 2024/5/8 22:43, Hailong Liu wrote: > > > > On Wed, 08. May 21:41, Gao Xiang wrote: > > > > > > > > > > +Cc Michal, > > > > > > > > > > On 2024/5/8 20:58, hailong.liu@oppo.com wrote: > > > > > > From: "Hailong.Liu" > > > > > > > > > > > > Commit a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc") > > > > > > includes support for __GFP_NOFAIL, but it presents a conflict with > > > > > > commit dd544141b9eb ("vmalloc: back off when the current task is > > > > > > OOM-killed"). A possible scenario is as belows: > > > > > > > > > > > > process-a > > > > > > kvcalloc(n, m, GFP_KERNEL | __GFP_NOFAIL) > > > > > > __vmalloc_node_range() > > > > > > __vmalloc_area_node() > > > > > > vm_area_alloc_pages() > > > > > > --> oom-killer send SIGKILL to process-a > > > > > > if (fatal_signal_pending(current)) break; > > > > > > --> return NULL; > > > > > > > > > > > > to fix this, do not check fatal_signal_pending() in vm_area_alloc_pages() > > > > > > if __GFP_NOFAIL set. > > > > > > > > > > > > Reported-by: Oven > > > > > > Signed-off-by: Hailong.Liu > > > > > > > > > > Why taging this as RFC here? It seems a corner-case fix of > > > > > commit a421ef303008 > > > > > > > > > > Thanks, > > > > > Gao Xiang > > > > > > > > > > > > > Hi Gao Xiang: > > > > > > > > RFC here to wait for a better way to handle this case :). > > > > IMO, if vmalloc support __GFP_NOFAIL it should not return > > > > null even system is deadlock on memory. > > > > > > The starting point is that kmalloc doesn't support __GFP_NOFAIL > > > if order > 1 (even for very short temporary uses), see: > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/page_alloc.c?h=v6.8#n2896 > > > > > > but it is possible if we have such page pointer array (since two > > > (order-1) pages can only keep 1024 8-byte entries, it can happen > > > if compression ratios are high), and kvmalloc(__GFP_NOFAIL) has > > > already been supported for almost two years, it will fallback to > > > order-0 allocation as described in commit e9c3cda4d86e > > > ("mm, vmalloc: fix high order __GFP_NOFAIL allocations"). > > > > > > With my limited understanding, I'm not sure why it can cause > > > deadlock here since it will fallback to order-0 allocation then, > > > and such allocation is just for short temporary uses again > > > because kmalloc doesn't support order > 1 short memory > > > allocation strictly. > > > > > > > deadlock on memory meands there is a memory leak causing > > system to be unable to allocate memory not actual > > *deadlock*. > > Where is memory leak? If it's caused by kvmalloc(__GFP_NOFAIL) > callers, then it's bugs of callers and we should fix the callers. > > Also why kmalloc(__GFP_NOFAIL) (for example, also order-0 > allocation) differs? > > Thanks, > Gao Xiang > I’m not suggesting that erofs would cause a memleak. What I mean is that if kvmalloc is invoked with __GFP_NOFAIL, it must ensure a non-NULL return, even in scenarios where memory leaks caused by other processes result in the inability to allocate a page. In such a situation, it should result in “Kernel panic - not syncing: System is deadlocked on memory”. > > > > > > Thanks, > > > Gao Xiang > > > > > > > -- > > > > Best Regards, > > Hailong. -- Best Regards, Hailong.