From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754856AbaH1S7t (ORCPT ); Thu, 28 Aug 2014 14:59:49 -0400 Received: from cantor2.suse.de ([195.135.220.15]:32865 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752234AbaH1Sgb (ORCPT ); Thu, 28 Aug 2014 14:36:31 -0400 From: Mel Gorman To: Jiri Slaby Cc: Linux-Stable , LKML , Mel Gorman Subject: [PATCH 42/97] mm: don't pointlessly use BUG_ON() for sanity check Date: Thu, 28 Aug 2014 19:34:50 +0100 Message-Id: <1409250945-30874-43-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.8.4.5 In-Reply-To: <1409250945-30874-1-git-send-email-mgorman@suse.de> References: <1409250945-30874-1-git-send-email-mgorman@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds commit 50f5aa8a9b248fa4262cf379863ec9a531b49737 upstream. BUG_ON() is a big hammer, and should be used _only_ if there is some major corruption that you cannot possibly recover from, making it imperative that the current process (and possibly the whole machine) be terminated with extreme prejudice. The trivial sanity check in the vmacache code is *not* such a fatal error. Recovering from it is absolutely trivial, and using BUG_ON() just makes it harder to debug for no actual advantage. To make matters worse, the placement of the BUG_ON() (only if the range check matched) actually makes it harder to hit the sanity check to begin with, so _if_ there is a bug (and we just got a report from Srivatsa Bhat that this can indeed trigger), it is harder to debug not just because the machine is possibly dead, but because we don't have better coverage. BUG_ON() must *die*. Maybe we should add a checkpatch warning for it, because it is simply just about the worst thing you can ever do if you hit some "this cannot happen" situation. Reported-by: Srivatsa S. Bhat Cc: Davidlohr Bueso Cc: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman --- mm/vmacache.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/vmacache.c b/mm/vmacache.c index d4224b3..1037a3ba 100644 --- a/mm/vmacache.c +++ b/mm/vmacache.c @@ -81,10 +81,12 @@ struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr) for (i = 0; i < VMACACHE_SIZE; i++) { struct vm_area_struct *vma = current->vmacache[i]; - if (vma && vma->vm_start <= addr && vma->vm_end > addr) { - BUG_ON(vma->vm_mm != mm); + if (!vma) + continue; + if (WARN_ON_ONCE(vma->vm_mm != mm)) + break; + if (vma->vm_start <= addr && vma->vm_end > addr) return vma; - } } return NULL; -- 1.8.4.5