Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 6 Dec 2023 10:25:12 +0800 | Subject | Re: [PATCH v4 2/4] bus: mhi: host: Drop chan lock before queuing buffers | From | Qiang Yu <> |
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On 11/30/2023 1:31 PM, Manivannan Sadhasivam wrote: > On Wed, Nov 29, 2023 at 11:29:07AM +0800, Qiang Yu wrote: >> On 11/28/2023 9:32 PM, Manivannan Sadhasivam wrote: >>> On Mon, Nov 27, 2023 at 03:13:55PM +0800, Qiang Yu wrote: >>>> On 11/24/2023 6:04 PM, Manivannan Sadhasivam wrote: >>>>> On Tue, Nov 14, 2023 at 01:27:39PM +0800, Qiang Yu wrote: >>>>>> Ensure read and write locks for the channel are not taken in succession by >>>>>> dropping the read lock from parse_xfer_event() such that a callback given >>>>>> to client can potentially queue buffers and acquire the write lock in that >>>>>> process. Any queueing of buffers should be done without channel read lock >>>>>> acquired as it can result in multiple locks and a soft lockup. >>>>>> >>>>> Is this patch trying to fix an existing issue in client drivers or a potential >>>>> issue in the future drivers? >>>>> >>>>> Even if you take care of disabled channels, "mhi_event->lock" acquired during >>>>> mhi_mark_stale_events() can cause deadlock, since event lock is already held by >>>>> mhi_ev_task(). >>>>> >>>>> I'd prefer not to open the window unless this patch is fixing a real issue. >>>>> >>>>> - Mani >>>> In [PATCH v4 1/4] bus: mhi: host: Add spinlock to protect WP access when >>>> queueing >>>> TREs, we add >>>> write_lock_bh(&mhi_chan->lock)/write_unlock_bh(&mhi_chan->lock) >>>> in mhi_gen_tre, which may be invoked as part of mhi_queue in client xfer >>>> callback, >>>> so we have to use read_unlock_bh(&mhi_chan->lock) here to avoid acquiring >>>> mhi_chan->lock >>>> twice. >>>> >>>> Sorry for confusing you. Do you think we need to sqush this two patch into >>>> one? >>> Well, if patch 1 is introducing a potential deadlock, then we should fix patch >>> 1 itself and not introduce a follow up patch. >>> >>> But there is one more issue that I pointed out in my previous reply. >> Sorry, I can not understand why "mhi_event->lock" acquired during >> mhi_mark_stale_events() can cause deadlock. In mhi_ev_task(), we will >> not invoke mhi_mark_stale_events(). Can you provide some interpretation? > Going by your theory that if a channel gets disabled while processing the event, > the process trying to disable the channel will try to acquire "mhi_event->lock" > which is already held by the process processing the event. > > - Mani OK, I get you. Thank you for kind explanation. Hopefully I didn't intrude too much. > >>> Also, I'm planning to cleanup the locking mess within MHI in the coming days. >>> Perhaps we can revisit this series at that point of time. Will that be OK for >>> you? >> Sure, that will be great. >>> - Mani >>> >>>>>> Signed-off-by: Qiang Yu <quic_qianyu@quicinc.com> >>>>>> --- >>>>>> drivers/bus/mhi/host/main.c | 4 ++++ >>>>>> 1 file changed, 4 insertions(+) >>>>>> >>>>>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c >>>>>> index 6c6d253..c4215b0 100644 >>>>>> --- a/drivers/bus/mhi/host/main.c >>>>>> +++ b/drivers/bus/mhi/host/main.c >>>>>> @@ -642,6 +642,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, >>>>>> mhi_del_ring_element(mhi_cntrl, tre_ring); >>>>>> local_rp = tre_ring->rp; >>>>>> + read_unlock_bh(&mhi_chan->lock); >>>>>> + >>>>>> /* notify client */ >>>>>> mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result); >>>>>> @@ -667,6 +669,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, >>>>>> kfree(buf_info->cb_buf); >>>>>> } >>>>>> } >>>>>> + >>>>>> + read_lock_bh(&mhi_chan->lock); >>>>>> } >>>>>> break; >>>>>> } /* CC_EOT */ >>>>>> -- >>>>>> 2.7.4 >>>>>> >>>>>>
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