Messages in this thread | | | Date | Wed, 19 Sep 2012 14:29:01 -0700 (PDT) | From | David Rientjes <> | Subject | Re: 3.6rc6 slab corruption. |
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On Wed, 19 Sep 2012, Konrad Rzeszutek Wilk wrote:
> From 0806b133b5b28081adf23d0d04a99636ed3b861b Mon Sep 17 00:00:00 2001 > From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Date: Wed, 19 Sep 2012 11:23:01 -0400 > Subject: [PATCH 1/2] debugfs: Add lock for u32_array_read > > Dave Jones spotted that the u32_array_read was doing something funny: > > ============================================================================= > BUG kmalloc-64 (Not tainted): Redzone overwritten > ----------------------------------------------------------------------------- > > INFO: 0xffff88001f4b4970-0xffff88001f4b4977. First byte 0xbb instead of 0xcc > INFO: Allocated in u32_array_read+0xd1/0x110 age=0 cpu=6 pid=32767 > __slab_alloc+0x516/0x5a5 > __kmalloc+0x213/0x2c0 > u32_array_read+0xd1/0x110 > .. snip.. > INFO: Freed in u32_array_read+0x99/0x110 age=0 cpu=0 pid=32749 > __slab_free+0x3f/0x3bf > kfree+0x2d5/0x310 > u32_array_read+0x99/0x110 > > Linus tracked it down and found out that "debugfs is racy for that case > [read calls in parallel on the debugfs]. At least the file->private_data > accesses are, for the case of that "u32_array" case. > > In fact it is racy in ... the whole "file->private_data" access .. > If you have multiple readers on the same file, the whole > > if (file->private_data) { > kfree(file->private_data); > file->private_data = NULL; > } > > file->private_data = format_array_alloc("%u", data->array, > data->elements); > > thing is just a disaster waiting to happen." He suggested > putting a lock which this patch does. >
Since these are non-seekable files, it must also race to find *ppos == 0.
> The consequence of this is that it will trigger more spinlock usage, > as this particular debugfs is used to provide a histogram of spinlock > contention. But memory corruption is a worst offender then that. > > Reported-by: Dave Jones <davej@redhat.com> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: David Rientjes <rientjes@google.com>
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