On 09/06/17 03:57, Luis R. Rodriguez wrote:
On Thu, Jun 8, 2017 at 6:10 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> 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
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