On Tue, Nov 19, 2019 at 9:49 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > The debug_dma_assert_idle() infrastructure was put in place to catch a > data corruption scenario first identified by the now defunct NET_DMA > receive offload feature. It caught cases where dma was in flight to a > stale page because the dma raced the cpu writing the page, and the cpu > write triggered cow_user_page(). > > However, the dma-debug tracking is overeager and also triggers in cases > where the dma device is reading from a page that is also undergoing > cow_user_page(). > > The fix proposed was originally posted in 2016, and Russell reported > "Yes, that seems to avoid the warning for me from an initial test", and > now Don is also reporting that this fix is addressing a similar false > positive report that he is seeing. > > Link: https://lore.kernel.org/r/CAPcyv4j8fWqwAaX5oCdg5atc+vmp57HoAGT6AfBFwaCiv0RbAQ@xxxxxxxxxxxxxx > Reported-by: Russell King <linux@xxxxxxxxxxxxxxx> > Reported-by: Don Dutile <ddutile@xxxxxxxxxx> > Fixes: 0abdd7a81b7e ("dma-debug: introduce debug_dma_assert_idle()") > Cc: <stable@xxxxxxxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Cc: Robin Murphy <robin.murphy@xxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > kernel/dma/debug.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 099002d84f46..11a6db53d193 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -587,7 +587,7 @@ void debug_dma_assert_idle(struct page *page) > } > spin_unlock_irqrestore(&radix_lock, flags); > > - if (!entry) > + if (!entry || entry->direction != DMA_FROM_DEVICE) > return; > > cln = to_cacheline_number(entry); If I am understanding right DMA_TO_DEVICE is fine, but won't you also need to cover the DMA_BIDIRECTIONAL case since it is possible for a device to also write the memory in that case?
