From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20130507035842.623244562@goodmis.org> Date: Mon, 06 May 2013 23:57:22 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Jan Stancek , David Rientjes , Hugh Dickins Subject: [010/126] mm: prevent mmap_cache race in find_vma() References: <20130507035712.909872333@goodmis.org> Content-Disposition: inline; filename=0010-mm-prevent-mmap_cache-race-in-find_vma.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.6.11.3 stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Stancek [ Upstream commit b6a9b7f6b1f21735a7456d534dc0e68e61359d2c ] 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 Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds Signed-off-by: Steven Rostedt --- 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 ae18a48..cf6434e 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1611,7 +1611,7 @@ 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 d4b0c10..a60db99 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -807,7 +807,7 @@ 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; -- 1.7.10.4