On Thu, Jun 8, 2017 at 6:10 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> wrote: > On Wed, Jun 7, 2017 at 10:54 AM, Martin Fuzzey <mfuzzey@xxxxxxxxxxx> wrote: >> On 07/06/17 19:08, Luis R. Rodriguez wrote: >>> >>> On Thu, May 25, 2017 at 10:28:38AM +0200, Fuzzey, Martin wrote: >>>> >>>> 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) Martin just to be clear, by "normal case termination" do you mean completing successfully ?? Ie the firmware actually did make it onto the device ? > 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
