Subject: Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on
 fallback
To: "Luis R. Rodriguez" <mcgrof@kernel.org>, linux-fsdevel@vger.kernel.org,
        Alan Cox <alan@linux.intel.com>, "Ted Ts'o" <tytso@mit.edu>,
        Andy Lutomirski <luto@kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>
References: <20170524205658.GK8951@wotan.suse.de>
 <20170524214027.7775-1-mcgrof@kernel.org>
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 <20170607170858.GK27288@wotan.suse.de>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Linux API <linux-api@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Greg KH <gregkh@linuxfoundation.org>, Daniel Wagner <wagi@monom.org>,
        David Woodhouse <dwmw2@infradead.org>, jewalt@lgsinnovations.com,
        rafal@milecki.pl, Arend Van Spriel <arend.vanspriel@broadcom.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "Li, Yi" <yi1.li@linux.intel.com>, atull@opensource.altera.com,
        Moritz Fischer <moritz.fischer@ettus.com>,
        Petr Mladek <pmladek@suse.com>,
        Johannes Berg <johannes.berg@intel.com>,
        Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
        Luca Coelho <luciano.coelho@intel.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        AKASHI Takahiro <takahiro.akashi@linaro.org>,
        David Howells <dhowells@redhat.com>, Peter Jones <pjones@redhat.com>,
        Hans de Goede <hdegoede@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: Martin Fuzzey <mfuzzey@parkeon.com>
Message-ID: <59383DDA.3040702@parkeon.com>
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