Messages in this thread | | | Date | Mon, 27 Nov 2023 15:13:55 +0800 | Subject | Re: [PATCH v4 2/4] bus: mhi: host: Drop chan lock before queuing buffers | From | Qiang Yu <> |
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On 11/24/2023 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? >> 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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