Messages in this thread | | | Date | Thu, 12 Mar 2009 12:54:10 +0100 | From | Martin Schwidefsky <> | Subject | Re: [PATCH] acquire mmap semaphore in pagemap_read. |
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On Thu, 12 Mar 2009 14:45:33 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> On Thu, Mar 12, 2009 at 11:33:08AM +0100, Martin Schwidefsky wrote: > > --- linux-2.6/fs/proc/task_mmu.c > > +++ linux-2.6-patched/fs/proc/task_mmu.c > > @@ -716,7 +716,9 @@ static ssize_t pagemap_read(struct file > > * user buffer is tracked in "pm", and the walk > > * will stop when we hit the end of the buffer. > > */ > > + down_read(&mm->mmap_sem); > > ret = walk_page_range(start_vaddr, end_vaddr, &pagemap_walk); > > + up_read(&mm->mmap_sem); > > This will introduce "put_user under mmap_sem" which is deadlockable.
Hmm, interesting. In this case the pagemap interface is fundamentally broken.
-- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
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