From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx113.postini.com [74.125.245.113]) by kanga.kvack.org (Postfix) with SMTP id 3A4B86B0002 for ; Tue, 2 Apr 2013 18:00:22 -0400 (EDT) Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r32M0J4Y022580 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 2 Apr 2013 18:00:19 -0400 From: Jan Stancek Subject: [PATCH] mm: prevent mmap_cache race in find_vma() Date: Tue, 2 Apr 2013 23:59:26 +0200 Message-Id: <3ae9b7e77e8428cfeb34c28ccf4a25708cbea1be.1364938782.git.jstancek@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org 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 --- mm/mmap.c | 2 +- mm/nommu.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 6466699..0db0de1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1940,7 +1940,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) /* 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; diff --git a/mm/nommu.c b/mm/nommu.c index e193280..2f3ea74 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -821,7 +821,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) 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; -- 1.7.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org