On Wed, Dec 06, 2023 at 10:25:12AM +0800, Qiang Yu wrote: > > 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. Not at all. Btw, did you actually encounter any issue that this patch is trying to fix? Or just fixing based on code inspection. - Mani > > > > > > 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@xxxxxxxxxxx> > > > > > > > --- > > > > > > > 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 > > > > > > > > > > > > > > -- மணிவண்ணன் சதாசிவம்
