linux-toradex.git/lib/dma-debug.c, branch v3.17-rc6

dma debug: account for cachelines and read-only mappings in overlap tracking

2014-03-04T15:55:47+00:00

While debug_dma_assert_idle() checks if a given *page* is actively
undergoing dma the valid granularity of a dma mapping is a *cacheline*.
Sander's testing shows that the warning message "DMA-API: exceeded 7
overlapping mappings of pfn..." is falsely triggering.  The test is
simply mapping multiple cachelines in a given page.

Ultimately we want overlap tracking to be valid as it is a real api
violation, so we need to track active mappings by cachelines.  Update
the active dma tracking to use the page-frame-relative cacheline of the
mapping as the key, and update debug_dma_assert_idle() to check for all
possible mapped cachelines for a given page.

However, the need to track active mappings is only relevant when the
dma-mapping is writable by the device.  In fact it is fairly standard
for read-only mappings to have hundreds or thousands of overlapping
mappings at once.  Limiting the overlap tracking to writable
(!DMA_TO_DEVICE) eliminates this class of false-positive overlap
reports.

Note, the radix gang lookup is sub-optimal.  It would be best if it
stopped fetching entries once the search passed a page boundary.
Nevertheless, this implementation does not perturb the original net_dma
failing case.  That is to say the extra overhead does not show up in
terms of making the failing case pass due to a timing change.

References:
  http://marc.info/?l=linux-netdev&m=139232263419315&w=2
  http://marc.info/?l=linux-netdev&m=139217088107122&w=2

Signed-off-by: Dan Williams 
Reported-by: Sander Eikelenboom 
Reported-by: Dave Jones 
Tested-by: Dave Jones 
Tested-by: Sander Eikelenboom 
Cc: Konrad Rzeszutek Wilk 
Cc: Francois Romieu 
Cc: Eric Dumazet 
Cc: Wei Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: fix overlap detection

2014-01-30T00:22:40+00:00

Commit 0abdd7a81b7e ("dma-debug: introduce debug_dma_assert_idle()") was
reworked to expand the overlap counter to the full range expressable by
3 tag bits, but it has a thinko in treating the overlap counter as a
pure reference count for the entry.

Instead of deleting when the reference-count drops to zero, we need to
delete when the overlap-count drops below zero.  Also, when detecting
overflow we can just test the overlap-count > MAX rather than applying
special meaning to 0.

Regression report available here:
http://marc.info/?l=linux-netdev&m=139073373932386&w=2

This patch, now tested on the original net_dma case, sees the expected
handful of reports before the eventual data corruption occurs.

Signed-off-by: Dan Williams 
Reported-by: Sander Eikelenboom 
Cc: Francois Romieu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: introduce debug_dma_assert_idle()

2014-01-22T00:19:41+00:00

Record actively mapped pages and provide an api for asserting a given
page is dma inactive before execution proceeds.  Placing
debug_dma_assert_idle() in cow_user_page() flagged the violation of the
dma-api in the NET_DMA implementation (see commit 77873803363c "net_dma:
mark broken").

The implementation includes the capability to count, in a limited way,
repeat mappings of the same page that occur without an intervening
unmap.  This 'overlap' counter is limited to the few bits of tag space
in a radix tree.  This mechanism is added to mitigate false negative
cases where, for example, a page is dma mapped twice and
debug_dma_assert_idle() is called after the page is un-mapped once.

Signed-off-by: Dan Williams 
Cc: Joerg Roedel 
Cc: Vinod Koul 
Cc: Russell King 
Cc: James Bottomley 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: update DMA debug API to better handle multiple mappings of a buffer

2013-03-22T23:41:20+00:00

There were reports of the igb driver unmapping buffers without calling
dma_mapping_error.  On closer inspection issues were found in the DMA
debug API and how it handled multiple mappings of the same buffer.

The issue I found is the fact that the debug_dma_mapping_error would
only set the map_err_type to MAP_ERR_CHECKED in the case that the was
only one match for device and device address.  However in the case of
non-IOMMU, multiple addresses existed and as a result it was not setting
this field once a second mapping was instantiated.  I have resolved this
by changing the search so that it instead will now set MAP_ERR_CHECKED
on the first buffer that matches the device and DMA address that is
currently in the state MAP_ERR_NOT_CHECKED.

A secondary side effect of this patch is that in the case of multiple
buffers using the same address only the last mapping will have a valid
map_err_type.  The previous mappings will all end up with map_err_type
set to MAP_ERR_CHECKED because of the dma_mapping_error call in
debug_dma_map_page.  However this behavior may be preferable as it means
you will likely only see one real error per multi-mapped buffer, versus
the current behavior of multiple false errors mer multi-mapped buffer.

Signed-off-by: Alexander Duyck 
Cc: Joerg Roedel 
Reviewed-by: Shuah Khan 
Tested-by: Shuah Khan 
Cc: Jakub Kicinski 
Cc: Konrad Rzeszutek Wilk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: fix locking bug in check_unmap()

2013-03-22T23:41:20+00:00

In check_unmap() it is possible to get into a dead-locked state if
dma_mapping_error is called.  The problem is that the bucket is locked in
check_unmap, and locked again by debug_dma_mapping_error which is called
by dma_mapping_error.  To resolve that we must release the lock on the
bucket before making the call to dma_mapping_error.

[akpm@linux-foundation.org: restore 80-col trickery to be consistent with the rest of the file]
Signed-off-by: Alexander Duyck 
Cc: Joerg Roedel 
Reviewed-by: Shuah Khan 
Tested-by: Shuah Khan 
Cc: Jakub Kicinski 
Cc: Konrad Rzeszutek Wilk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: fix to not have dependency on get_dma_ops() interface

2012-11-17T12:06:41+00:00

dma-debug depends on get_dma_ops() interface. Several architectures
do not define dma_ops and get_dma_ops(). When dma debug interfaces are
used on an architecture (e.g: c6x) that doesn't define get_dmap_ops(),
compilation fails. Changing dma-debug to call dma_mapping_error() instead
of defining its own that calls get_dma_ops(), such that the internal use of
dma_mapping_error() doesn't interfere with the debug_dma_mapping_error()
interface's mapping error checks. Moving dma_mapping_error() checks in
check_unmap() under the dma debug entry not found is sufficient to fix the
problem.

Reference: https://lkml.org/lkml/2012/10/26/367

Signed-off-by: Shuah Khan 
Reported-by: Mark Salter 
Signed-off-by: Joerg Roedel

dma-debug: New interfaces to debug dma mapping errors

2012-10-24T15:06:43+00:00

Add dma-debug interface debug_dma_mapping_error() to debug
drivers that fail to check dma mapping errors on addresses
returned by dma_map_single() and dma_map_page() interfaces.
This interface clears a flag set by debug_dma_map_page() to
indicate that dma_mapping_error() has been called by the
driver. When driver does unmap, debug_dma_unmap() checks the
flag and if this flag is still set, prints warning message
that includes call trace that leads up to the unmap. This
interface can be called from dma_mapping_error() routines to
enable dma mapping error check debugging.

Tested: Intel iommu and swiotlb (iommu=soft) on x86-64 with
        CONFIG_DMA_API_DEBUG enabled and disabled.

Signed-off-by: Shuah Khan 
Reviewed-by: Konrad Rzeszutek Wilk 
Signed-off-by: Joerg Roedel

lib/dma-debug.c: fix __hash_bucket_find()

2012-10-19T21:07:48+00:00

If there is only one match, the unique matched entry should be returned.

Without the fix, the upcoming dma debug interfaces ("dma-debug: new
interfaces to debug dma mapping errors") can't work reliably because
only device and dma_addr are passed to dma_mapping_error().

Signed-off-by: Ming Lei 
Reported-by: Wu Fengguang 
Cc: Joerg Roedel 
Tested-by: Shuah Khan 
Cc: Paul Gortmaker 
Cc: Jakub Kicinski 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

dma-debug: Remove local BUS_NOTIFY_UNBOUND_DRIVER define

2012-10-02T10:10:27+00:00

Remove local BUS_NOTIFY_UNBOUND_DRIVER define. This is not used since
BUS_NOTIFY_UNBOUND_DRIVER is defined in include/linux/device.h

Signed-off-by: Shuah Khan 
Signed-off-by: Joerg Roedel

dma-debug: debugfs_create_bool() takes a u32 pointer

2012-07-02T10:11:40+00:00

Even though it has "bool" in the name, you have pass a u32 pointer to
debugfs_create_bool().  Otherwise you get memory corruption in
write_file_bool().  Fortunately in this case the corruption happens in
an alignment hole between variables so it doesn't cause any problems.

Signed-off-by: Dan Carpenter 
Signed-off-by: Joerg Roedel