From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: x86/mce: suspicious RCU usage in 4.13.4 From: "Luck, Tony" Message-Id: <20171016182843.wrtcelsqf2y2onze@intel.com> Date: Mon, 16 Oct 2017 11:28:43 -0700 To: Borislav Petkov Cc: Andi Kleen , Jeremy Cline , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , "linux-edac@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Laura Abbott List-ID: T24gU3VuLCBPY3QgMTUsIDIwMTcgYXQgMTE6NDA6NDZBTSArMDIwMCwgQm9yaXNsYXYgUGV0a292 IHdyb3RlOgo+IE9uIFdlZCwgT2N0IDExLCAyMDE3IGF0IDA5OjM0OjIyUE0gKzAwMDAsIEx1Y2ss IFRvbnkgd3JvdGU6Cj4gPiA+IGhlcmUncyBhIHNlY29uZCBhdHRlbXB0IGF0IGEgbW9yZSByaWdv cm91cyBzaW1wbGlmaWNhdGlvbjogUkNVIHN0dWZmIGlzCj4gPiA+IGdvbmUgYW5kIG9ubHkgYSBz aW5nbGUgbG9vcCBzY2FucyB0aHJvdWdoIHRoZSBlbGVtZW50cy4KPiA+IAo+ID4gVGhlIGRldl9t Y2VfbG9nKCkgY2hhbmdlcyBsb29rIGdvb2Qgbm93Lgo+ID4gCj4gPiBZb3UgY2FuIGFwcGx5IHRo ZSBheGUgdG8gbW9yZSBiaXRzIG9mIG1jZV9jaHJkZXZfcmVhZCgpIHRob3VnaC4gTGlrZSB0aGF0 Cj4gCj4gVGhhdCBwcm92b2tlZCBhIHZlcnkgc2VyaW91cyBheGluZy4gUGxlYXNlIGNoZWNrIHdo ZXRoZXIgSSB3ZW50IHRvbyBmYXIuIEh1bmsKPiBiZWxvdyBpcyBvbnRvcCBvZiB3aGF0IGdvdCBh eGVkIGFscmVhZHk6CgpJIHRoaW5rIGEgZmV3IG1vcmUgbGluZXMgY2FuIGdvLiAgQWxtb3N0IGV2 ZXJ5dGhpbmcgcmVsYXRpbmcgdG8gdGhlICJmaW5pc2hlZCIKZWxlbWVudC4gZGV2X21jZV9sb2co KSBtdXN0IHN0aWxsIHNldCBpdCAoYmVjYXVzZSB0aGUgdXNlciBtb2RlIG1jZWxvZyg4KQpkYWVt b24gd2lsbCBncnVtYmxlIGlmIHdlIGdpdmUgaXQgcmVjb3JkcyB0aGF0IGRvbid0IGhhdmUgaXQg c2V0KS4gQnV0CnNpbmNlIGV2ZXJ5dGhpbmcgaXMgcHJvdGVjdGVkIGJ5IG1jZV9jaHJkZXZfcmVh ZF9tdXRleCB3ZSBjYW4ndCBoYXZlCiJPbGQgbGVmdCBvdmVyIGVudHJpZXMiIHRvIHNraXAuIE5v ciBpcyB0aGVyZSBhbnkgd2F5IHRoYXQgZmluaXNoZWQgY2FuJ3QKYmUgc2V0IGZvciBhbiBlbnRy eSBpbiAwLi5tY2Vsb2cubmV4dCB3aGVuIGl0IGNvbWVzIHRvIG1jZV9jaHJkZXZfcmVhZCgpLgoK VGhpcyBwYXRjaCBvbiB0b3Agb2YgeW91ciB0d28/Pz8KCi1Ub255Ci0tLQpUbyB1bnN1YnNjcmli ZSBmcm9tIHRoaXMgbGlzdDogc2VuZCB0aGUgbGluZSAidW5zdWJzY3JpYmUgbGludXgtZWRhYyIg aW4KdGhlIGJvZHkgb2YgYSBtZXNzYWdlIHRvIG1ham9yZG9tb0B2Z2VyLmtlcm5lbC5vcmcKTW9y ZSBtYWpvcmRvbW8gaW5mbyBhdCAgaHR0cDovL3ZnZXIua2VybmVsLm9yZy9tYWpvcmRvbW8taW5m by5odG1sCgpkaWZmIC0tZ2l0IGEvYXJjaC94ODYva2VybmVsL2NwdS9tY2hlY2svZGV2LW1jZWxv Zy5jIGIvYXJjaC94ODYva2VybmVsL2NwdS9tY2hlY2svZGV2LW1jZWxvZy5jCmluZGV4IDE3ZDJi YWIyNTcyMC4uN2Y4NWI3NmY0M2JjIDEwMDY0NAotLS0gYS9hcmNoL3g4Ni9rZXJuZWwvY3B1L21j aGVjay9kZXYtbWNlbG9nLmMKKysrIGIvYXJjaC94ODYva2VybmVsL2NwdS9tY2hlY2svZGV2LW1j ZWxvZy5jCkBAIC00OSwxMSArNDksNyBAQCBzdGF0aWMgaW50IGRldl9tY2VfbG9nKHN0cnVjdCBu b3RpZmllcl9ibG9jayAqbmIsIHVuc2lnbmVkIGxvbmcgdmFsLAogCiAJbXV0ZXhfbG9jaygmbWNl X2NocmRldl9yZWFkX211dGV4KTsKIAotCWZvciAoZW50cnkgPSBtY2Vsb2cubmV4dDsgZW50cnkg PCBNQ0VfTE9HX0xFTjsgZW50cnkrKykgewotCQkvKiBPbGQgbGVmdCBvdmVyIGVudHJ5LiBTa2lw OiAqLwotCQlpZiAobWNlbG9nLmVudHJ5W2VudHJ5XS5maW5pc2hlZCkKLQkJCWNvbnRpbnVlOwot CX0KKwllbnRyeSA9IG1jZWxvZy5uZXh0OwogCiAJLyoKIAkgKiBXaGVuIHRoZSBidWZmZXIgZmls bHMgdXAgZGlzY2FyZCBuZXcgZW50cmllcy4gQXNzdW1lIHRoYXQgdGhlCkBAIC0yMzEsOSArMjI3 LDYgQEAgc3RhdGljIHNzaXplX3QgbWNlX2NocmRldl9yZWFkKHN0cnVjdCBmaWxlICpmaWxwLCBj aGFyIF9fdXNlciAqdWJ1ZiwKIAlmb3IgKGkgPSAwOyBpIDwgbmV4dDsgaSsrKSB7CiAJCXN0cnVj dCBtY2UgKm0gPSAmbWNlbG9nLmVudHJ5W2ldOwogCi0JCWlmICghbS0+ZmluaXNoZWQpCi0JCQlj b250aW51ZTsKLQogCQllcnIgfD0gY29weV90b191c2VyKGJ1ZiwgbSwgc2l6ZW9mKCptKSk7CiAJ CWJ1ZiArPSBzaXplb2YoKm0pOwogCX0K From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756560AbdJPS2q (ORCPT ); Mon, 16 Oct 2017 14:28:46 -0400 Received: from mga09.intel.com ([134.134.136.24]:55432 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754947AbdJPS2o (ORCPT ); Mon, 16 Oct 2017 14:28:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.43,387,1503385200"; d="scan'208";a="1025756511" Date: Mon, 16 Oct 2017 11:28:43 -0700 From: "Luck, Tony" To: Borislav Petkov Cc: Andi Kleen , Jeremy Cline , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , "linux-edac@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Laura Abbott Subject: Re: x86/mce: suspicious RCU usage in 4.13.4 Message-ID: <20171016182843.wrtcelsqf2y2onze@intel.com> References: <9840bf0d-6756-75eb-1a2d-d3aace235244@redhat.com> <20171010194426.s7keveirclglx6vh@pd.tnic> <20171010200841.uhniuwc7pulqgmic@intel.com> <871smasqux.fsf@linux.intel.com> <20171011115020.i4gkcy5pjifh2zsm@pd.tnic> <3908561D78D1C84285E8C5FCA982C28F770038E5@ORSMSX114.amr.corp.intel.com> <20171015094046.6477zglnee3s75lc@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171015094046.6477zglnee3s75lc@pd.tnic> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 15, 2017 at 11:40:46AM +0200, Borislav Petkov wrote: > On Wed, Oct 11, 2017 at 09:34:22PM +0000, Luck, Tony wrote: > > > here's a second attempt at a more rigorous simplification: RCU stuff is > > > gone and only a single loop scans through the elements. > > > > The dev_mce_log() changes look good now. > > > > You can apply the axe to more bits of mce_chrdev_read() though. Like that > > That provoked a very serious axing. Please check whether I went too far. Hunk > below is ontop of what got axed already: I think a few more lines can go. Almost everything relating to the "finished" element. dev_mce_log() must still set it (because the user mode mcelog(8) daemon will grumble if we give it records that don't have it set). But since everything is protected by mce_chrdev_read_mutex we can't have "Old left over entries" to skip. Nor is there any way that finished can't be set for an entry in 0..mcelog.next when it comes to mce_chrdev_read(). This patch on top of your two??? -Tony diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c index 17d2bab25720..7f85b76f43bc 100644 --- a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c +++ b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c @@ -49,11 +49,7 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val, mutex_lock(&mce_chrdev_read_mutex); - for (entry = mcelog.next; entry < MCE_LOG_LEN; entry++) { - /* Old left over entry. Skip: */ - if (mcelog.entry[entry].finished) - continue; - } + entry = mcelog.next; /* * When the buffer fills up discard new entries. Assume that the @@ -231,9 +227,6 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf, for (i = 0; i < next; i++) { struct mce *m = &mcelog.entry[i]; - if (!m->finished) - continue; - err |= copy_to_user(buf, m, sizeof(*m)); buf += sizeof(*m); }