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Message-ID: <20160108232352.GA13046@node.shutemov.name>
Date: Sat, 9 Jan 2016 01:23:52 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Dmitry Vyukov <dvyukov@...gle.com>, Michal Hocko <mhocko@...e.cz>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Oleg Nesterov <oleg@...hat.com>,
Chen Gang <gang.chen.5i5j@...il.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: mm: possible deadlock in mm_take_all_locks
On Fri, Jan 08, 2016 at 05:58:33PM +0100, Dmitry Vyukov wrote:
> Hello,
>
> I've hit the following deadlock warning while running syzkaller fuzzer
> on commit b06f3a168cdcd80026276898fd1fee443ef25743. As far as I
> understand this is a false positive, because both call stacks are
> protected by mm_all_locks_mutex.
+Michal
I don't think it's false positive.
The reason we don't care about order of taking i_mmap_rwsem is that we
never takes i_mmap_rwsem under other i_mmap_rwsem, but that's not true for
i_mmap_rwsem vs. hugetlbfs_i_mmap_rwsem_key. That's why we have the
annotation in the first place.
See commit b610ded71918 ("hugetlb: fix lockdep splat caused by pmd
sharing").
Consider totally untested patch below.
diff --git a/mm/mmap.c b/mm/mmap.c
index 2ce04a649f6b..63aefcf409e1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3203,7 +3203,16 @@ int mm_take_all_locks(struct mm_struct *mm)
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (signal_pending(current))
goto out_unlock;
- if (vma->vm_file && vma->vm_file->f_mapping)
+ if (vma->vm_file && vma->vm_file->f_mapping &&
+ !is_vm_hugetlb_page(vma))
+ vm_lock_mapping(mm, vma->vm_file->f_mapping);
+ }
+
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ if (signal_pending(current))
+ goto out_unlock;
+ if (vma->vm_file && vma->vm_file->f_mapping &&
+ is_vm_hugetlb_page(vma))
vm_lock_mapping(mm, vma->vm_file->f_mapping);
}
--
Kirill A. Shutemov
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