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    SubjectRe: 3.14-mw regression: rtl8169 WARNING: DMA-API: exceeded 7 overlapping mappings of pfn 55ebe

    Thursday, February 13, 2014, 9:14:47 PM, you wrote:

    > On Tue, 2014-02-11 at 20:17 -0800, Eric Dumazet wrote:
    >> On Tue, 2014-02-11 at 18:07 -0800, Dan Williams wrote:
    >>
    >> > The overlap granularity is too large. Multiple dma_map_single
    >> > mappings are allowed to a given page as long as they don't collide on
    >> > the same cache line.
    >> >
    >>
    >> I am not sure why you try number of mappings of a page.
    >>
    >> Try launching 100 concurrent netperf -t TCP_SENFILE
    >>
    >> Same page might be mapped more than 100 times, more than 10000 times in
    >> some cases.

    > Thanks for that test case.

    > I updated the fix patch with the following.

    > diff --git a/lib/dma-debug.c b/lib/dma-debug.c
    > index 42b12740940b..611010df1e9c 100644
    > --- a/lib/dma-debug.c
    > +++ b/lib/dma-debug.c
    > @@ -513,6 +513,13 @@ static int active_cln_insert(struct dma_debug_entry *entry)
    > unsigned long flags;
    > int rc;
    >
    > + /* If the device is not writing memory then we don't have any
    > + * concerns about the cpu consuming stale data. This mitigates
    > + * legitimate usages of overlapping mappings.
    > + */
    + if (entry->>direction == DMA_TO_DEVICE)
    > + return 0;
    > +
    > spin_lock_irqsave(&radix_lock, flags);
    > rc = radix_tree_insert(&dma_active_cacheline, to_cln(entry), entry);
    > if (rc == -EEXIST)
    > @@ -526,6 +533,10 @@ static void active_cln_remove(struct dma_debug_entry *entry)
    > {
    > unsigned long flags;
    >
    > + /* ...mirror the insert case */
    + if (entry->>direction == DMA_TO_DEVICE)
    > + return;
    > +
    > spin_lock_irqsave(&radix_lock, flags);
    > /* since we are counting overlaps the final put of the
    > * cacheline will occur when the overlap count is 0.


    > Sander, barring a negative test result from you I'll send the attached
    > patch to Andrew.

    Hi Dan,

    That seems to effectively suppress the warning, thanks and:

    Tested-by; Sander Eikelenboom <linux@eikelenboom.it>

    --
    Sander

    > --
    > Dan




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