Re: [PATCH v2] firmware: fix batched requests - wake all waiters

[Luis R. Rodriguez]

On Thu, Jun 29, 2017 at 05:17:15PM +0200, Greg KH wrote:
> On Thu, Jun 29, 2017 at 05:16:41PM +0200, Greg KH wrote:
> > On Mon, Jun 26, 2017 at 02:23:12PM -0700, Luis R. Rodriguez wrote:
> > > From: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> > > 
> > > The firmware cache mechanism serves two purposes, the secondary purpose is
> > > not well documented nor understood. This fixes a regression with the secondary
> > > purpose of the firmware cache mechanism: batched requests.
> > > 
> > > The firmware cache is used for:
> > > 
> > > 1) Addressing races with file lookups during the suspend/resume cycle
> > >    by keeping firmware in memory during the cycle
> > > 
> > > 2) Batched requests for the same file rely only on work from the first file
> > >    lookup, which keeps the firmware in memory until the last release_firmware()
> > >    is called
> > > 
> > > Batched requests *only* take effect if secondary requests come in prior to the
> > > first user calling release_firmware(). The devres name used for the internal
> > > firmware cache is used as a hint other pending requests are ongoing, the
> > > firmware buffer data is kept in memory until the last user of the buffer
> > > calls release_firmware(), therefore serializing requests and delaying the
> > > release until all requests are done.
> > > 
> > > Batched requests wait for a wakup or signal (we only accept SIGKILL now) so we
> > > can rely on the first file fetch to write to the pending secondary requests.
> > > Commit 5b029624948d ("firmware: do not use fw_lock for fw_state protection")
> > > ported the firmware API to use swait, and in doing so failed to convert
> > > complete_all() to swake_up_all() -- it used swake_up(), loosing the ability
> > > for *some* batched requests to take effect.
> > > 
> > > Without this fix it has been reported plugging in two Intel 6260 Wifi cards
> > > on a system will end up enumerating the two devices only 50% of the time
> > > [0]. The ported swake_up() should have actually two devices, however,
> > > *if more than two cards are used* the swake_up() would not suffice. This
> > > change is only part of the required fixes for batched requests. Subsequent
> > > fixes will follow.
> > > 
> > > This particular change should fix the cases where more than three requests
> > > with the same firmware name is used, otherwise batched requests will wait for
> > > MAX_SCHEDULE_TIMEOUT and just timeout eventually.
> > > 
> > > [0] https://bugzilla.kernel.org/show_bug.cgi?id=195477
> > > 
> > > Fixes: 5b029624948d ("firmware: do not use fw_lock for fw_state protection")
> > > CC: <stable@xxxxxxxxxxxxxxx>    [4.10+]
> > > Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> > > Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> > > [mcgrof: expanded on impact on commit log]
> > > Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> > > ---
> > > 
> > > Greg, I think it would make sense to queue this in after the signal stable
> > > fixes [1].
> > 
> > As I just dropped them, can you redo this based on Linus's tree now?
> 
> Oh nevermind, it does apply to that tree now.  Wait, what am I supposed
> to do here?
> 
> confused,

Yea..  and moving way from swait actually means this should be applied first,
just that this patch becomes a port back away from swait. The signal series of
fixes are patches which should be applied even before swait.

Since this can be confusing I'm just going to fold this patch into the other larger
series. That should make order clear.

  Luis