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

On Fri, Jun 09, 2017 at 09:40:47AM +0200, Martin Fuzzey wrote:

On 09/06/17 03:57, Luis R. Rodriguez wrote:

quoted

On Thu, Jun 8, 2017 at 6:10 PM, Luis R. Rodriguez [off-list ref] wrote:

quoted

quoted

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.

Thanks this could mean we also *should* trigger a failure if init is issuing
modprobe on a series of drivers and one completes before another while
request_firmware() is called on init or probe on a subsequent driver. If true
I'm surprised this never was reported back when the fallback mechanism was
popular, I suppose it was not an issue given most firmware *was* present on
/lib/firmware/ and the direct filesystem lookup first step always found the
firmware first, so this would only be an issue for folks relying on the
fallback mechanism exclusively.

Will include a test case based on your above script. Thanks!

  Luis