On 2019-01-14 10:29 a.m., Christoph Hellwig wrote:
On Mon, Jan 14, 2019 at 11:24:49PM +0800, wangbo wrote:
wd719x_host_reset get spinlock first then call wd719x_chip_init,
so replace GFP_KERNEL with GFP_ATOMIC in wd719x_chip_init.
Please move the allocation outside the lock instead. GFP_ATOMIC
DMA allocations are generally a bad idea and should be avoided where
we can.
More importantly we should never actually trigger the allocation
under the lock as far as fw_virt will always be set already
in that case.
So I think you can safely move the request firmware + allocation
+ memcpy from wd719x_chip_init to wd719x_board_found, but I'd rather
have Ondrej review that plan.
Further to this, the result of holding a lock (probably with _irqsave()
tacked onto it) during a GFP_KERNEL is a message like this in the log:
hrtimer: interrupt took 1084 ns
It is not always easy to find since it is a "_once" message. The sg v3
driver (the one in production) produces these. I have been able to stamp
them out by taking care in the sg v4 driver (in testing) around
allocations. It also meant adding a new state in my state machine to
fend off "bad things" happening to that object while it is unlocked.
So there may be a cost to dropping the lock.
Doug Gilbert
