Messages in this thread | | | Subject | Re: [PATCH 0/4] firmware: fix fallback mechanism by ignoring SIGCHLD | From | Martin Fuzzey <> | Date | Thu, 15 Jun 2017 09:49:18 +0200 |
| |
On 15/06/17 00:20, Luis R. Rodriguez wrote: > Martin reported an issue with Android where if sysfs is used to trigger a sync > fw load which *relies* on the fallback mechanism and a background job completes > while the trigger is ongoing in the foreground it will immediately fail the fw > request. The issue can be observed in this simple test script using the > test_firmware driver: > > set -e > /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 "does-not-exist-file.bin" > "$DIR"/trigger_request > > The background sleep triggers the SIGCHLD signal and we fail the firmware > request on the fallback mechanism. This was due to the type of wait used which > ... > > Note that although I *feared* this might implicate any use of non-killable waits > on other system calls, such as finit_module(), initial testing confirms this to > not be the case. For instance replacing the echo with modprobe on a module > which does the same on init does not present the same issues. This could be due > to the special SA_RESTART flag case on write() as noted above and sysfs... > however, its not perfectly clear yet to me. > > The reason the problem does not occur with modprobe is that in that case the processes triggering the firmware load (modprobe) and the process dying (sleep) are *siblings* rather than father and child. So the modprobe process does *not* receive a SIGCHLD when its' *brother* dies.
echo is a shell built-in so the process triggering the firmware load (the shell) and the process dying (sleep) *are* father and child.
Martin
| |