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[209.85.208.170]) by smtp.gmail.com with ESMTPSA id e14sm172109lfn.165.2020.10.23.08.53.06 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Oct 2020 08:53:07 -0700 (PDT) Received: by mail-lj1-f170.google.com with SMTP id d24so2066674ljg.10 for ; Fri, 23 Oct 2020 08:53:06 -0700 (PDT) X-Received: by 2002:a2e:898c:: with SMTP id c12mr1248002lji.285.1603468386475; Fri, 23 Oct 2020 08:53:06 -0700 (PDT) MIME-Version: 1.0 References: <20201023050214.GG23681@linux.intel.com> In-Reply-To: <20201023050214.GG23681@linux.intel.com> From: Linus Torvalds Date: Fri, 23 Oct 2020 08:52:50 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [LTP] mmstress[1309]: segfault at 7f3d71a36ee8 ip 00007f3d77132bdf sp 00007f3d71a36ee8 error 4 in libc-2.27.so[7f3d77058000+1aa000] To: Sean Christopherson Cc: =?UTF-8?B?RGFuaWVsIETDrWF6?= , Naresh Kamboju , Stephen Rothwell , "Matthew Wilcox (Oracle)" , zenglg.jy@cn.fujitsu.com, "Peter Zijlstra (Intel)" , Viresh Kumar , X86 ML , open list , lkft-triage@lists.linaro.org, "Eric W. Biederman" , linux-mm , linux-m68k , Linux-Next Mailing List , Thomas Gleixner , kasan-dev , Dmitry Vyukov , Geert Uytterhoeven , Christian Brauner , Ingo Molnar , LTP List , Al Viro Content-Type: text/plain; charset="UTF-8" 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 Thu, Oct 22, 2020 at 10:02 PM Sean Christopherson wrote: > > I haven't reproduced the crash, but I did find a smoking gun that confirms the > "register shenanigans are evil shenanigans" theory. I ran into a similar thing > recently where a seemingly innocuous line of code after loading a value into a > register variable wreaked havoc because it clobbered the input register. Yup, that certainly looks like the smoking gun. Thanks for finding an example of this, clearly I'll have to either go back to the "conditionally use 'A' or 'a' depending on size" model, or perhaps try Rasmus' patch. Linus