Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937523Ab3DJW5m (ORCPT ); Wed, 10 Apr 2013 18:57:42 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56595 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937434Ab3DJWuJ (ORCPT ); Wed, 10 Apr 2013 18:50:09 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jan Stancek , David Rientjes , Hugh Dickins , Linus Torvalds , Ben Hutchings Subject: [ 26/29] mm: prevent mmap_cache race in find_vma() Date: Wed, 10 Apr 2013 15:49:44 -0700 Message-Id: <20130410224806.782757072@linuxfoundation.org> X-Mailer: git-send-email 1.8.1.rc1.5.g7e0651a In-Reply-To: <20130410224804.061806042@linuxfoundation.org> References: <20130410224804.061806042@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3052 Lines: 86 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Stancek commit b6a9b7f6b1f21735a7456d534dc0e68e61359d2c upstream. find_vma() can be called by multiple threads with read lock held on mm->mmap_sem and any of them can update mm->mmap_cache. Prevent compiler from re-fetching mm->mmap_cache, because other readers could update it in the meantime: thread 1 thread 2 | find_vma() | find_vma() struct vm_area_struct *vma = NULL; | vma = mm->mmap_cache; | if (!(vma && vma->vm_end > addr | && vma->vm_start <= addr)) { | | mm->mmap_cache = vma; return vma; | ^^ compiler may optimize this | local variable out and re-read | mm->mmap_cache | This issue can be reproduced with gcc-4.8.0-1 on s390x by running mallocstress testcase from LTP, which triggers: kernel BUG at mm/rmap.c:1088! Call Trace: ([<000003d100c57000>] 0x3d100c57000) [<000000000023a1c0>] do_wp_page+0x2fc/0xa88 [<000000000023baae>] handle_pte_fault+0x41a/0xac8 [<000000000023d832>] handle_mm_fault+0x17a/0x268 [<000000000060507a>] do_protection_exception+0x1e2/0x394 [<0000000000603a04>] pgm_check_handler+0x138/0x13c [<000003fffcf1f07a>] 0x3fffcf1f07a Last Breaking-Event-Address: [<000000000024755e>] page_add_new_anon_rmap+0xc2/0x168 Thanks to Jakub Jelinek for his insight on gcc and helping to track this down. Signed-off-by: Jan Stancek Acked-by: David Rientjes Signed-off-by: Hugh Dickins Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context, indentation] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- mm/mmap.c | 2 +- mm/nommu.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1619,7 +1619,7 @@ struct vm_area_struct *find_vma(struct m if (mm) { /* Check the cache first. */ /* (Cache hit rate is typically around 35%.) */ - vma = mm->mmap_cache; + vma = ACCESS_ONCE(mm->mmap_cache); if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) { struct rb_node * rb_node; --- a/mm/nommu.c +++ b/mm/nommu.c @@ -807,7 +807,7 @@ struct vm_area_struct *find_vma(struct m struct vm_area_struct *vma; /* check the cache first */ - vma = mm->mmap_cache; + vma = ACCESS_ONCE(mm->mmap_cache); if (vma && vma->vm_start <= addr && vma->vm_end > addr) return vma; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/