Messages in this thread | | | Date | Thu, 16 May 2013 09:44:49 -0400 | Subject | Re: [PATCH -next] ashmem: Fix ashmem_shrink deadlock. | From | Robert Love <> |
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On Thu, May 16, 2013 at 4:15 AM, Raul Xiong <raulxiong@gmail.com> wrote: > The issue happens in such sequence: > ashmem_mmap acquired ashmem_mutex --> ashmem_mutex:shmem_file_setup > called kmem_cache_alloc --> shrink due to low memory --> ashmem_shrink > tries to acquire the same ashmem_mutex -- it blocks here. > > I think this reports the bug clearly. Please have a look.
There is no debate about the nature of the bug. Only the fix.
My mutex_trylock patch fixes the problem. I prefer that solution.
Andrew's suggestion of GFP_ATOMIC won't work as we'd have to propagate that down into shmem and elsewhere.
Using PF_MEMALLOC will work. You'd want to define something like:
static int set_memalloc(void) { if (current->flags & PF_MEMALLOC) return 0; current->flags |= PF_MEMALLOC; return 1; }
static void clear_memalloc(int memalloc) { if (memalloc) current->flags &= ~PF_MEMALLOC; }
and then set/clear PF_MEMALLOC around every memory allocation and function that descends into a memory allocation. As said I prefer my solution but if someone wants to put together a patch with this approach, fine by me.
Robert
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