From b8e35885679ef5f44dab1c100219b82eae7a1c13 Mon Sep 17 00:00:00 2001 From: Jan Stancek Date: Thu, 4 Apr 2013 11:35:10 -0700 Subject: mm: prevent mmap_cache race in find_vma() 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 --- mm/mmap.c | 2 +- mm/nommu.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) (limited to 'mm') diff --git a/mm/mmap.c b/mm/mmap.c index eae90af60ea..dff37a68623 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1573,7 +1573,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) 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; diff --git a/mm/nommu.c b/mm/nommu.c index f59e170fceb..f0cd7abd337 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; -- cgit v1.2.3-18-g5258