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

On Wed, Jun 7, 2017 at 10:54 AM, Martin Fuzzey [off-list ref] wrote:

On 07/06/17 19:08, Luis R. Rodriguez wrote:

quoted

On Thu, May 25, 2017 at 10:28:38AM +0200, Fuzzey, Martin wrote:

quoted

1) Android init calls write() on the sysfs file
2) The sysfs .store() callback registered by a driver is called
3) The driver calls request_firmware()
4) request_firmware() sends the firmware load request to userspace and
calls wait_for_completion_interruptible()

Martin, just for completeness on documenting on the commit log of the next
swait proposed fix for this -- what signal did the process get from which
you
note the child dies below ? Exactly what in Android sent this signal ?

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)

Interesting, could one interpretation here be that the process
successfully finishing + the signal being sent beats out the timing of
the firmware_class syfs code detecting that the write completed ?

5) Kernel delivers SIGCHLD to pid=1 to tell it a child has died, which
causes -ERESTARTSYS to be returned from wait_*

  Luis