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From: "Toke Høiland-Jørgensen" <toke@toke.dk>
To: Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>, Maxime Bizon <mbizon@freebox.fr>
Cc: Oleksandr Natalenko <oleksandr@natalenko.name>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Halil Pasic <pasic@linux.ibm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Kalle Valo <kvalo@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Olha Cherevyk <olha.cherevyk@gmail.com>,
	iommu <iommu@lists.linux-foundation.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Netdev <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable <stable@vger.kernel.org>
Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP
Date: Thu, 24 Mar 2022 18:07:29 +0100	[thread overview]
Message-ID: <871qyr9t4e.fsf@toke.dk> (raw)
In-Reply-To: <d8a1cbf4-a521-78ec-1560-28d855e0913e@arm.com>

Robin Murphy <robin.murphy@arm.com> writes:

> On 2022-03-24 16:31, Christoph Hellwig wrote:
>> On Thu, Mar 24, 2022 at 05:29:12PM +0100, Maxime Bizon wrote:
>>>> I'm looking into this; but in the interest of a speedy resolution of
>>>> the regression I would be in favour of merging that partial revert
>>>> and reinstating it if/when we identify (and fix) any bugs in ath9k :)
>>>
>>> This looks fishy:
>>>
>>> ath9k/recv.c
>>>
>>>                  /* We will now give hardware our shiny new allocated skb */
>>>                  new_buf_addr = dma_map_single(sc->dev, requeue_skb->data,
>>>                                                common->rx_bufsize, dma_type);
>>>                  if (unlikely(dma_mapping_error(sc->dev, new_buf_addr))) {
>>>                          dev_kfree_skb_any(requeue_skb);
>>>                          goto requeue_drop_frag;
>>>                  }
>>>
>>>                  /* Unmap the frame */
>>>                  dma_unmap_single(sc->dev, bf->bf_buf_addr,
>>>                                   common->rx_bufsize, dma_type);
>>>
>>>                  bf->bf_mpdu = requeue_skb;
>>>                  bf->bf_buf_addr = new_buf_addr;
>> 
>> Creating a new mapping for the same buffer before unmapping the
>> previous one does looks rather bogus.  But it does not fit the
>> pattern where revering the sync_single changes make the driver
>> work again.
>
> OK, you made me look :)
>
> Now that it's obvious what to look for, I can only conclude that during 
> the stanza in ath_edma_get_buffers(), the device is still writing to the 
> buffer while ownership has been transferred to the CPU, and whatever got 
> written while ath9k_hw_process_rxdesc_edma() was running then gets wiped 
> out by the subsequent sync_for_device, which currently resets the 
> SWIOTLB slot to the state that sync_for_cpu copied out. By the letter of 
> the DMA API that's not allowed, but on the other hand I'm not sure if we 
> even have a good idiom for "I can't tell if the device has finished with 
> this buffer or not unless I look at it" :/

Right, but is that sync_for_device call really needed? AFAICT, that
ath9k_hw_process_rxdesc_edma() invocation doesn't actually modify any of
the data when it returns EINPROGRESS, so could we just skip it? Like
the patch below? Or am I misunderstanding the semantics here?

-Toke


diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
index 0c0624a3b40d..19244d4c0ada 100644
--- a/drivers/net/wireless/ath/ath9k/recv.c
+++ b/drivers/net/wireless/ath/ath9k/recv.c
@@ -647,12 +647,8 @@ static bool ath_edma_get_buffers(struct ath_softc *sc,
                                common->rx_bufsize, DMA_FROM_DEVICE);
 
        ret = ath9k_hw_process_rxdesc_edma(ah, rs, skb->data);
-       if (ret == -EINPROGRESS) {
-               /*let device gain the buffer again*/
-               dma_sync_single_for_device(sc->dev, bf->bf_buf_addr,
-                               common->rx_bufsize, DMA_FROM_DEVICE);
+       if (ret == -EINPROGRESS)
                return false;
-       }
 
        __skb_unlink(skb, &rx_edma->rx_fifo);
        if (ret == -EINVAL) {

  reply	other threads:[~2022-03-24 17:07 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-23  7:19 [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP Oleksandr Natalenko
2022-03-23  7:28 ` Kalle Valo
2022-03-23 17:27 ` Linus Torvalds
2022-03-23 19:06   ` Robin Murphy
2022-03-23 19:16     ` Linus Torvalds
2022-03-23 20:54       ` Robin Murphy
2022-03-24  5:57         ` Christoph Hellwig
2022-03-24 10:25           ` Oleksandr Natalenko
2022-03-24 11:05             ` Robin Murphy
2022-03-24 14:27               ` Toke Høiland-Jørgensen
2022-03-24 16:29                 ` Maxime Bizon
2022-03-24 16:31                   ` Christoph Hellwig
2022-03-24 16:52                     ` Robin Murphy
2022-03-24 17:07                       ` Toke Høiland-Jørgensen [this message]
2022-03-24 19:26                         ` Linus Torvalds
2022-03-24 21:14                           ` Toke Høiland-Jørgensen
2022-03-25 10:25                           ` Maxime Bizon
2022-03-25 11:27                             ` Robin Murphy
2022-03-25 23:38                               ` Halil Pasic
2022-03-26 16:05                                 ` Toke Høiland-Jørgensen
2022-03-26 18:38                                   ` Linus Torvalds
2022-03-26 22:38                                     ` David Laight
2022-03-26 22:41                                       ` Linus Torvalds
2022-03-25 16:25                             ` Toke Høiland-Jørgensen
2022-03-25 16:45                               ` Robin Murphy
2022-03-25 18:13                                 ` Toke Høiland-Jørgensen
2022-03-25 18:30                             ` Linus Torvalds
2022-03-25 19:14                               ` Robin Murphy
2022-03-25 19:21                                 ` Linus Torvalds
2022-03-25 19:26                               ` Oleksandr Natalenko
2022-03-25 19:27                                 ` Linus Torvalds
2022-03-25 19:35                                   ` Oleksandr Natalenko
2022-03-25 20:37                               ` Johannes Berg
2022-03-25 20:47                                 ` Linus Torvalds
2022-03-25 21:13                                   ` Johannes Berg
2022-03-25 21:40                                     ` David Laight
2022-03-25 21:56                                     ` Linus Torvalds
2022-03-25 22:41                                       ` David Laight
2022-03-27  3:15                                     ` Halil Pasic
2022-03-28  9:48                                       ` Johannes Berg
2022-03-28  9:50                                         ` Johannes Berg
2022-03-28  9:57                                           ` Johannes Berg
2022-03-27  3:48                           ` Halil Pasic
2022-03-27  5:06                             ` Linus Torvalds
2022-03-27  5:21                               ` Linus Torvalds
2022-03-27 15:24                                 ` David Laight
2022-03-27 19:23                                   ` Linus Torvalds
2022-03-27 20:04                                     ` Linus Torvalds
2022-03-27 23:52                                 ` Halil Pasic
2022-03-28  0:30                                   ` Linus Torvalds
2022-03-28 12:02                                     ` Halil Pasic
2022-03-27 23:37                               ` Halil Pasic
2022-03-28  0:37                                 ` Linus Torvalds
2022-03-25  7:12                         ` Oleksandr Natalenko
2022-03-25  9:21                           ` Thorsten Leemhuis
2022-03-24 18:31                       ` Halil Pasic
2022-03-25 16:31                         ` Christoph Hellwig
2022-03-24 18:02         ` Halil Pasic
2022-03-25 15:25           ` Halil Pasic
2022-03-25 16:23             ` Robin Murphy
2022-03-25 16:32           ` Christoph Hellwig
2022-03-25 18:15             ` Toke Høiland-Jørgensen
2022-03-25 18:42               ` Robin Murphy
2022-03-25 18:46                 ` Linus Torvalds
2022-03-28  6:37                   ` Christoph Hellwig
2022-03-28  8:15                     ` David Laight
2022-03-30 12:11                     ` Halil Pasic
2022-03-24  8:55   ` Oleksandr Natalenko

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