Messages in this thread | | | Date | Sat, 16 Dec 2017 12:14:27 -0200 | From | Mauro Carvalho Chehab <> | Subject | Re: [PATCH 1/2] bdisp: Fix a possible sleep-in-atomic bug in bdisp_hw_reset |
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Em Sat, 16 Dec 2017 19:53:55 +0800 Jia-Ju Bai <baijiaju1990@gmail.com> escreveu:
> Hi, > > On 2017/12/15 22:51, Fabien DESSENNE wrote: > > Hi > > > > On 12/12/17 14:47, Jia-Ju Bai wrote: > >> The driver may sleep under a spinlock. > >> The function call path is: > >> bdisp_device_run (acquire the spinlock) > >> bdisp_hw_reset > >> msleep --> may sleep > >> > >> To fix it, msleep is replaced with mdelay. > > May I suggest you to use readl_poll_timeout_atomic (instead of the whole > > "for" block): this fixes the problem and simplifies the code? > > Okay, I have submitted a patch according to your advice. > You can have a look :)
This can still be usind mdelay() to wait for a long time.
It doesn't seem wise to do that, as it could cause system contention. Couldn't this be reworked in a way to avoid having the spin locked while sleeping?
Once we had a similar issue on Siano, and it was solved by this
commit 3cdadc50bbe8f04c1231c8af614cafd7ddd622bf Author: Richard Zidlicky <rz@linux-m68k.org> Date: Tue Aug 24 09:52:36 2010 -0300
V4L/DVB: dvb: fix smscore_getbuffer() logic
Drivers shouldn't sleep while holding a spinlock. A previous workaround were to release the spinlock before callinc schedule().
This patch uses a different approach: it just waits for the siano hardware to answer.
Signed-off-by: Richard Zidlicky <rz@linux-m68k.org> Cc: stable@kernel.org Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
The code as changed to use wait_event() at the kthread that was waiting for data to arrive. Only when the data is ready, the code with the spin lock is called.
It made the driver a way more stable, and didn't add any penalties of needing to do long delays on a non-interruptible code.
Thanks, Mauro
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