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List:       linux-kernel
Subject:    Re: bade page state while calling munmap() for kmalloc'ed UIO
From:       Andrew Morton <akpm () linux-foundation ! org>
Date:       2011-08-31 23:13:07
Message-ID: 20110831161307.d605848b.akpm () linux-foundation ! org
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On Wed, 31 Aug 2011 11:58:25 +0200
"Hans J. Koch" <hjk@hansjkoch.de> wrote:

> On Mon, Aug 29, 2011 at 05:05:47PM +0200, Jan Altenberg wrote:
> 
> [Since we got no reply on linux-mm, I added lkml and Andrew to Cc: (mm doesn't
> seem to have a maintainer...)]
> 
> > Hi,
> > 
> > I'm currently analysing a problem similar to some mmap() issue reported
> > in the past: https://lkml.org/lkml/2010/7/11/140
> 
> The arch there was microblaze, and you are working on arm. That means
> the problem appears on at least to archs.
> 
> > 
> > So, what I'm trying to do is mapping some physically continuous memory
> > (allocated by kmalloc) to userspace, using a trivial UIO driver (the
> > idea is that a device can directly DMA to that buffer):
> > 
> > [...]
> > #define MEM_SIZE (4 * PAGE_SIZE)
> > 
> > addr = kmalloc(MEM_SIZE, GFP_KERNEL)
> > [...]
> > info.mem[0].addr = (unsigned long) addr;
> > info.mem[0].internal_addr = addr;
> > info.mem[0].size = MEM_SIZE;
> > info.mem[0].memtype = UIO_MEM_LOGICAL;
> > [...]
> > ret = uio_register_device(&pdev->dev, &info);
> > 
> > Userspace maps that memory range and writes its contents to a file:
> > 
> > [...]
> > 
> > fd = open("/dev/uio0", O_RDWR);
> > if (fd < 0) {
> >            perror("Can't open UIO device\n");
> >            exit(1);
> > }
> > 
> > mem_map = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
> >                   MAP_PRIVATE, fd, 0);
> > 
> > if(mem_map == MAP_FAILED) {
> >            perror("Can't map UIO memory\n");
> >            ret = -ENOMEM;
> >            goto out_file;
> > }
> > [...]
> > bytes_written = write(fd_file, mem_map, MAP_SIZE)
> > [...]
> > 
> > munmap(mem_map);
> 
> >From my point of view (I've got Jan's full test case code), this
> is a completely correct UIO use case.
> 
> > 
> > So, what happens is (I'm currently testing with 3.0.3 on ARM
> > VersatilePB): When I do the munmap(), I run into the following error:
> > 
> > BUG: Bad page state in process uio_test  pfn:078ed
> > page:c0409154 count:0 mapcount:0 mapping:  (null) index:0x0
> > page flags: 0x284(referenced|slab|arch_1)

PG_slab is set.  The kernel is complaining because a page which was
allocated via kmalloc/kmem_cache_alloc was directly passed to the page
allocator for freeing.  It should have been passed to kfree().

Presumably the uio driver expects that its memory was allocated via
alloc_pages(), not via kmalloc().

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