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Received-SPF: Pass (protection.outlook.com: domain of oppo.com designates 58.252.5.68 as permitted sender) receiver=protection.outlook.com; client-ip=58.252.5.68; helo=mail.oppo.com; pr=C Received: from mail.oppo.com (58.252.5.68) by HK2PEPF00006FB5.mail.protection.outlook.com (10.167.8.11) 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 03:33:29 +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 11:33:29 +0800 Date: Thu, 9 May 2024 11:33:28 +0800 From: Hailong Liu To: Barry Song <21cnbao@gmail.com> CC: , , , , , , , , Oven Subject: Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL Message-ID: <20240509033328.q2gwgaurpeg2mqqi@oppo.com> References: <20240508125808.28882-1-hailong.liu@oppo.com> MIME-Version: 1.0 Content-Type: text/plain; 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May 14:20, Barry Song wrote: > On Thu, May 9, 2024 at 12:58 AM 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 > > --- > > mm/vmalloc.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 6641be0ca80b..2f359d08bf8d 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -3560,7 +3560,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid, > > > > /* High-order pages or fallback path if "bulk" fails. */ > > while (nr_allocated < nr_pages) { > > - if (fatal_signal_pending(current)) > > + if (!(gfp & __GFP_NOFAIL) && fatal_signal_pending(current)) > > break; > > why not !nofail ? if order = 0, nofail would not be set true in bulk allocator. in such a case, it is still possible to break early > > This seems a correct fix, but it undermines the assumption made in > commit dd544141b9eb > ("vmalloc: back off when the current task is OOM-killed") > > " > This may trigger some hidden problems, when caller does not handle > vmalloc failures, or when rollaback after failed vmalloc calls own > vmallocs inside. However all of these scenarios are incorrect: vmalloc > does not guarantee successful allocation, it has never been called with > __GFP_NOFAIL and threfore either should not be used for any rollbacks or > should handle such errors correctly and not lead to critical failures. > " > > If a significant kvmalloc operation is performed with the NOFAIL flag, it risks > reverting the fix intended to address the OOM-killer issue in commit > dd544141b9eb. > Should we indeed permit the NOFAIL flag for large kvmalloc allocations? IMO, if we encounter this issue, it should be fixed by the caller, not here. > > > Thanks > Barry -- Best Regards, Hailong.