Messages in this thread | | | Date | Wed, 29 Nov 2023 11:29:07 +0800 | Subject | Re: [PATCH v4 2/4] bus: mhi: host: Drop chan lock before queuing buffers | From | Qiang Yu <> |
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On 11/28/2023 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? > > 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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