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

Joerg Roedel joerg.roedel at amd.com
Fri Jan 9 08:19:14 PST 2009


this is version 2 of the patchset which introduces code to debug drivers
usage of the DMA-API. Many thanks to all the reviewers and the useful
comments on the fist version of this patchset. Tests with hardware
IOMMUs have shown several bugs in drivers regarding the usage of that
API.  Problems were found especially in network card drivers.

These bugs often don't show up or have any negative impact if there is
no hardware IOMMU in use in the system. But with an hardware IOMMU these
bugs turn the hardware unusable or, in the worst case, cause data
corruption on devices which are managed by other (good) drivers.

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

------------[ 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 way driver developers get an idea where the problem is in their

I hope I addressed most of the review comments and objections from the
first version. Please give this version also a good review and send me
your comments.



Changes from v1 -> v2:

- moved code to lib/ and include/linux to make it usable for all
- more fine grained hash locking (locking is now per hash bucket, no
  global lock anymore)
- dma_debug_entries are preallocated
- per default the code will only print one warning and is silent then
- added a debugfs interface to see some statistics and to enable more
  verbose error reporting in the kernel log
- added command line parameter to disable debugging code
- allocation errors are now handled correctly
- added documentation about this facility for driver developers


 Documentation/DMA-API.txt           |  117 ++++++
 Documentation/kernel-parameters.txt |   10 +
 arch/Kconfig                        |    2 +
 arch/x86/Kconfig                    |    1 +
 arch/x86/include/asm/dma-mapping.h  |   30 ++-
 arch/x86/kernel/pci-dma.c           |    5 +
 include/linux/dma-debug.h           |  154 ++++++++
 lib/Kconfig.debug                   |   11 +
 lib/Makefile                        |    2 +
 lib/dma-debug.c                     |  726 +++++++++++++++++++++++++++++++++++
 10 files changed, 1054 insertions(+), 4 deletions(-)

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