Subject: Re: [PATCH 0/16] DMA-API debugging facility v2

From: Joerg Roedel <[email-masked]>
Date: Fri, 9 Jan 2009 23:33:27 +0100

On Fri, Jan 09, 2009 at 01:24:24PM -0800, Michael Chan wrote:
> 
> On Fri, 2009-01-09 at 08:19 -0800, Joerg Roedel wrote:
> > 
> > With the code these patches introduce driver developers can find several
> > bugs of misusing the DMA-API in their drivers. But be aware, it can not
> > find all possible bugs. If it finds a problem it prints out messages
> > like
> > 
> > ------------[ cut here ]------------
> > WARNING: at /data2/repos/linux.trees.git/lib/dma-debug.c:231 check_unmap+0xab/0x3d9()
> > Hardware name: Toonie
> > bnx2 0000:01:00.0: DMA-API: device driver tries to free DMA memory it has not allocated [device address=0x00000000011]
> > Modules linked in:
> > Pid: 0, comm: swapper Not tainted 2.6.28 #174
> > Call Trace:
> >  <IRQ>  [<ffffffff8105af3a>] warn_slowpath+0xd3/0xf2
> >  [<ffffffff8107c36f>] ? find_usage_backwards+0xe2/0x116
> >  [<ffffffff8107c36f>] ? find_usage_backwards+0xe2/0x116
> >  [<ffffffff812efd16>] ? usb_hcd_link_urb_to_ep+0x94/0xa0
> >  [<ffffffff8107c52b>] ? mark_lock+0x1c/0x364
> >  [<ffffffff8107d8f7>] ? __lock_acquire+0xaec/0xb55
> >  [<ffffffff8107c52b>] ? mark_lock+0x1c/0x364
> >  [<ffffffff811e2b4b>] ? get_hash_bucket+0x28/0x33
> >  [<ffffffff814b25a5>] ? _spin_lock_irqsave+0x69/0x75
> >  [<ffffffff811e2b4b>] ? get_hash_bucket+0x28/0x33
> >  [<ffffffff811e2ff2>] check_unmap+0xab/0x3d9
> >  [<ffffffff8107c9ed>] ? trace_hardirqs_on_caller+0x108/0x14a
> >  [<ffffffff8107ca3c>] ? trace_hardirqs_on+0xd/0xf
> >  [<ffffffff811e3433>] debug_unmap_single+0x3e/0x40
> >  [<ffffffff8128d2d8>] dma_unmap_single+0x3d/0x60
> >  [<ffffffff8128d335>] pci_unmap_page+0x1c/0x1e
> >  [<ffffffff81290759>] bnx2_poll_work+0x626/0x8cb
> >  [<ffffffff8107d8f7>] ? __lock_acquire+0xaec/0xb55
> >  [<ffffffff81070100>] ? run_posix_cpu_timers+0x49c/0x603
> >  [<ffffffff81070000>] ? run_posix_cpu_timers+0x39c/0x603
> >  [<ffffffff8107c52b>] ? mark_lock+0x1c/0x364
> >  [<ffffffff8107d8f7>] ? __lock_acquire+0xaec/0xb55
> >  [<ffffffff81292804>] bnx2_poll_msix+0x33/0x81
> >  [<ffffffff813b6478>] net_rx_action+0x8a/0x139
> >  [<ffffffff8105ff39>] __do_softirq+0x8b/0x147
> >  [<ffffffff8102933c>] call_softirq+0x1c/0x34
> >  [<ffffffff8102a611>] do_softirq+0x39/0x90
> >  [<ffffffff8105fde8>] irq_exit+0x4e/0x98
> >  [<ffffffff8102a5c2>] do_IRQ+0x11f/0x135
> >  [<ffffffff81028b93>] ret_from_intr+0x0/0xf
> >  <EOI> <4>---[ end trace 4339d58302097423 ]---
> > 
> This was triggered during pci_unmap_page() -> dma_unmap_single() where
> check_unmap() did not find the entry.
> 
> The original mapping was done in bnx2 using pci_map_page().  I did not
> see how the debug entry was added to the hash during the call to
> pci_map_page() -> dma_map_page().  Did I miss something?

dma_map_page() results in dma_map_single() -> debug_map_single() call on
x86. This way the entry would be added. Maybe the error from a double
free?

Joerg