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@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
