Messages in this thread | | | Subject | Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback | From | Martin Fuzzey <> | Date | Wed, 7 Jun 2017 19:54:34 +0200 |
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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) 5) Kernel delivers SIGCHLD to pid=1 to tell it a child has died, which causes -ERESTARTSYS to be returned from wait_*
Martin
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