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Thu, 23 Sep 2021 17:16:21 -0700 (PDT) Date: Thu, 23 Sep 2021 20:16:19 -0400 From: Peter Xu To: Li Wang Cc: Nadav Amit , Andrew Morton , linux-kernel , Linux-MM , linux-fsdevel@vger.kernel.org, Nadav Amit , Andrea Arcangeli , stable@vger.kernel.org Subject: Re: [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap() Message-ID: References: <20210921200247.25749-1-namit@vmware.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EC3CD900013E X-Stat-Signature: fe39c1rmjem186unieb6efepzxeub74d Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=O9ThL9A8; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf29.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com X-HE-Tag: 1632442584-487321 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Sep 22, 2021 at 05:06:53PM +0800, Li Wang wrote: > Hi, Li, > > I confirmed this patch (applied on 5.14) gets rid of the below userfaultfd > test failure. > > # ./userfaultfd anon 16 2 > nr_pages: 4096, nr_pages_per_cpu: 256 > bounces: 1, mode: rnd read, userfaults: 313 missing > (51+34+37+26+41+28+15+20+16+12+13+7+10+2+0+1) 995 wp > (121+79+96+53+90+104+48+61+56+82+56+41+49+26+11+22) > bounces: 0, mode: read, userfaults: 64 missing > (15+8+10+6+5+2+4+3+3+1+4+0+0+2+0+1) 2157 wp > (223+274+189+141+116+132+203+153+143+126+110+114+101+66+42+24) > testing uffd-wp with pagemap (pgsize=4096): done > testing uffd-wp with pagemap (pgsize=2097152): done > testing UFFDIO_ZEROPAGE: done. > testing signal delivery: done. > testing events (fork, remap, remove): ERROR: nr 3933 memory corruption 0 1 > (errno=0, line=963) > ERROR: faulting process failed (errno=0, line=1117) Just to keep a record within this thread - my understanding is above issue is a separate issue from what Nadav has fixed. The other fix could be: https://lore.kernel.org/lkml/20210923232512.210092-1-peterx@redhat.com/ When verify with Nadav's patch, please check whether you have thp enabled globally: # echo always > /sys/kernel/mm/transparent_hugepage/enabled Thanks, -- Peter Xu