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

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Date:   Tue, 6 Jun 2017 18:47:34 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Alan Cox <alan@...ux.intel.com>, fsdevel@...r.kernel.org,
        Stephen Boyd <stephen.boyd@...aro.org>,
        "Li, Yi" <yi1.li@...ux.intel.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Fuzzey, Martin" <mfuzzey@...keon.com>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Wagner <wagi@...om.org>,
        David Woodhouse <dwmw2@...radead.org>,
        jewalt@...innovations.com, rafal@...ecki.pl,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        atull@...nsource.altera.com,
        Moritz Fischer <moritz.fischer@...us.com>,
        Petr Mladek <pmladek@...e.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        David Howells <dhowells@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Hans de G oede <hdegoede@...hat.com>,
        Ted Ts'o <tytso@....edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on
 fallback

Adding fsdevel folks.

On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > "Unix tradition (and thus almost all applications) believe file store
> > writes to
> > be non signal interruptible. It would not be safe or practical to
> > change that
> > guarantee."
> 
> Yep everyone codes
> 
> 	write(disk_file, "foo", 3);
> 
> not while(..) blah around it.

Thanks for the confirmation! That's a simple enough explanation.

> > For these two reasons then it would seem best we do two things
> > actually:
> > 
> > 1) return -EINTR instead of -EAGAIN when we detect
> > swait_event_interruptible_timeout()
> > got interrupted by a signal (it returns -ERESTARTSYS)
> > 2) Do as you note below and add wait_event_killable_timeout()
> 
> Pedantic detail that I don't think affects you
> 
> If you have completed a part of the I/O then you should return the byte
> processed count not EINTR, but -1,EINTR if no progress was made.

You are right with some new exceptions and with regards to the future:

The syfs loading interface for firmware currently goes through the
data file exposed on syfs, the respective write op firmware_data_write()
only checks for signals at the beginning. After that its a full one
swoop try to write if you are following the old tradition and are using
a buffer allocated by the firmware API.

If you are using the relatively new request_firmware_into_buf() added
by Stephen Boyd which lets the driver provide the allocated buffer then
we have a loop in firmware_rw() which should be fixed to:

1) Check for signals
2) Do what you noted above.

Furthermore Yi Li over at Intel is adding some new API calls which would
re-use some of this for FPGA firmwares which are also very large, that
work should consider the above and fix appropriately as well.

  Luis