Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

[Martin Fuzzey <mfuzzey-mB3Nsq4MPf1BDgjK7y7TUQ@public.gmane.org>]

On 09/06/17 03:57, Luis R. Rodriguez wrote:
> On Thu, Jun 8, 2017 at 6:10 PM, Luis R. Rodriguez <mcgrof-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
>>> Android didn't send the signal, the kernel did (SIGCHLD).
>>>
>>> Like this:
>>>
>>> 1) Android init (pid=1) fork()s (say pid=42) [this child process is totally
>>> unrelated to firmware loading]
>>> 2) Android init (pid=1) does a write() on a (driver custom) sysfs file which
>>> ends up calling request_firmware() kernel side
>>> 3) The firmware loading fallback mechanism is used, the request is sent to
>>> userspace and pid 1 waits in the kernel on wait_*
>>> 4) before firmware loading completes pid 42 dies (for any reason - in my
>>> case normal termination)
> Martin just to be clear, by "normal case termination" do you mean
> completing successfully ?? Ie the firmware actually did make it onto
> the device ?

The firmware did *not* make it onto the device since the 
request_firmware() call returned an error
(the code that would have transfered it to the device is only executed 
following a successful request_firmware)

The process that terminates normally is unrelated to firmware loading as 
I said above.

The only things that matter are:
- It is a child process of the process that calls request_firmware()
- It terminates *while* the the wait_ is still in progress


Here is a way of reproducing the problem using the test_firmware module 
(which I only just saw) on normal linux with no Android or custom driver


#!/bin/sh
set -e

# Make sure the system firmware loader doesn't get in the way
/etc/init.d/udev stop

modprobe test_firmware

DIR=/sys/devices/virtual/misc/test_firmware

echo 10 >/sys/class/firmware/timeout;
sleep 2 &
echo -n "/some/non/existing/file.bin" > "$DIR"/trigger_request;



If run with the "sleep 2 &" it terminates after 2 seconds
If the sleep is commented it runs for the expected 10 seconds (the 
firmware loading timeout)

Since the sleep process is a child of the script process requesting a 
firmware load its death causes a SIGCHLD causing request_firmware() to 
abort prematurely.


Martin