Hi Mani,
On 4/18/20 12:19 PM, Manivannan Sadhasivam wrote:
Hi Hemant,
Please try to use an email client supporting plain text mode like mutt. Your reply looks mangled.
On 18 April 2020 12:40:10 PM IST, Hemant Kumar <hemantk@xxxxxxxxxxxxxx> wrote:
Hi Mani,
On 4/17/20 3:14 AM, Manivannan Sadhasivam wrote:
Hi Hemant,
On Thu, Apr 16, 2020 at 08:37:16PM -0700, Hemant Kumar wrote:
On 4/7/20 7:33 AM, Manivannan Sadhasivam wrote:
Hi Dan,
On Tue, Apr 07, 2020 at 04:55:59PM +0300, Dan Carpenter wrote:
Hello Manivannan Sadhasivam,
The patch 189ff97cca53: "bus: mhi: core: Add support for data
transfer" from Feb 20, 2020, leads to the following static checker
warning:
drivers/bus/mhi/core/main.c:1153 mhi_queue_buf()
error: double locked 'mhi_chan->lock' (orig line 1110)
drivers/bus/mhi/core/main.c
1142 }
1143
1144 /* Toggle wake to exit out of M2 */
1145 mhi_cntrl->wake_toggle(mhi_cntrl);
1146
1147 if (mhi_chan->dir == DMA_TO_DEVICE)
1148 atomic_inc(&mhi_cntrl->pending_pkts);
1149
1150 if (likely(MHI_DB_ACCESS_VALID(mhi_cntrl))) {
1151 unsigned long flags;
1152
1153 read_lock_irqsave(&mhi_chan->lock,
flags);
parse_xfer_event is taking read lock :
read_lock_bh(&mhi_chan->lock); first
and later
mhi_queue_buf takes read lock: read_lock_irqsave(&mhi_chan->lock,
flags);
Both are read locks which are recursive, is this problematic ?
read_locks are recursive but I wanted to make the static checker
happy. But
looking into it further (and after having a chat with Arnd), we might
need to
refactor the locking here.
Since 'chan->lock' only prevents 'mhi_chan->ch_state', how about
doing something
like below?
As comment mentioned for OOB (to enter DB mode) write lock is acquired
with preemption disabled (irqsave ver). In case of OOB event control
does not go to mhi_queue_buf
path.
Again, why do we need irq version of write lock. It should only be used if the data is shared with hardirq handlers which I don't see. Otherwise, write_lock_bh() looks sufficient to me as this itself is an exclusive lock.
irq ver disables preemption where as bh ver does not. In case of OOB
event, idea is not get preempted and this is for short duration of
ringing the channel doorbell.
For transfer completion events >read_lock_bh is acquired and
channel state is checked.
This lock is held for entire handling of the transfer completion so
that
in case
__mhi_unprepare_channel() is called from power down context write lock
is acquired
for channel lock to change channel state, which would wait until
parse_xfer_event for
data transfer is done (reader is in critical section). In case if
__mhi_unprepare_channel() wins then
parse_xfer_event is skipped otherwise parse_xfer_event is done and then
channel state is changed.
So if we get unprepare_channel() after checking the channel state in parse_xfer_event(), what could go wrong?
Also, grabbing the lock for the entire function doesn't look good to me. The purpose of the chan->lock is just to protect 'chan_state'/DB and not the whole function.
main problem unprepare_channel and parse_xfer_event have lot in common
due to that we can not let them run in parallel. For example
-parse_xfer_event is working on transfer ring (rp and wp updates)
-parse_xfer_event calling dma_unmap_single on buffer
-__mhi_unprepare_channel() calling mhi_reset_chan() and
mhi_deinit_chan_ctxt().
Thanks,
Mani
diff --git a/drivers/bus/mhi/core/main.c
b/drivers/bus/mhi/core/main.c
index 3e9aa3b2da77..904f9be7a142 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -474,19 +474,12 @@ static int parse_xfer_event(struct
mhi_controller *mhi_cntrl,
result.transaction_status = (ev_code == MHI_EV_CC_OVERFLOW)
?
-EOVERFLOW : 0;
- /*
- * If it's a DB Event then we need to grab the lock
- * with preemption disabled and as a write because we
- * have to update db register and there are chances that
- * another thread could be doing the same.
- */
- if (ev_code >= MHI_EV_CC_OOB)
- write_lock_irqsave(&mhi_chan->lock, flags);
- else
- read_lock_bh(&mhi_chan->lock);
-
- if (mhi_chan->ch_state != MHI_CH_STATE_ENABLED)
- goto end_process_tx_event;
+ read_lock_bh(&mhi_chan->lock);
+ if (mhi_chan->ch_state != MHI_CH_STATE_ENABLED) {
+ read_unlock_bh(&mhi_chan->lock);
+ return 0;
+ }
+ read_unlock_bh(&mhi_chan->lock);
switch (ev_code) {
case MHI_EV_CC_OVERFLOW:
@@ -559,10 +552,12 @@ static int parse_xfer_event(struct
mhi_controller *mhi_cntrl,
mhi_chan->db_cfg.db_mode = 1;
read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
+ write_lock_irqsave(&mhi_chan->lock, flags);
if (tre_ring->wp != tre_ring->rp &&
MHI_DB_ACCESS_VALID(mhi_cntrl)) {
mhi_ring_chan_db(mhi_cntrl, mhi_chan);
}
+ write_unlock_irqrestore(&mhi_chan->lock, flags);
read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
break;
}
@@ -572,12 +567,6 @@ static int parse_xfer_event(struct
mhi_controller *mhi_cntrl,
break;
} /* switch(MHI_EV_READ_CODE(EV_TRB_CODE,event)) */
-end_process_tx_event:
- if (ev_code >= MHI_EV_CC_OOB)
- write_unlock_irqrestore(&mhi_chan->lock, flags);
- else
- read_unlock_bh(&mhi_chan->lock);
-
return 0;
}
Moreover, I do have couple of concerns:
1. 'mhi_chan->db_cfg.db_mode = 1' needs to be added to the critical
section
above.
2. Why we have {write/read}_lock_irq variants for chan->lock? I don't
see where
the db or ch_state got shared with hardirq handler. Maybe we should
only have
*_bh (softirq) variants all over the place?
Thanks,
Mani
^^^^^^^^^^^^^^^
The caller is already holding this lock.
Hmm. We have one internal user of this function and that's where
the locking
has gone wrong. Will fix it.
Thanks for reporting!
Regards,
Mani
1154 mhi_ring_chan_db(mhi_cntrl, mhi_chan);
1155 read_unlock_irqrestore(&mhi_chan->lock,
flags);
1156 }
1157
1158 read_unlock_irqrestore(&mhi_cntrl->pm_lock,
flags);
1159
1160 return 0;
1161 }
1162 EXPORT_SYMBOL_GPL(mhi_queue_buf);
regards,
dan carpenter
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Forum,
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--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
