Date: Thu, 29 Jun 2017 17:16:41 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: jakub.kicinski@netronome.com, nbroeking@me.com, ming.lei@redhat.com,
        mfuzzey@parkeon.com, ebiederm@xmission.com, dmitry.torokhov@gmail.com,
        wagi@monom.org, dwmw2@infradead.org, jewalt@lgsinnovations.com,
        rafal@milecki.pl, arend.vanspriel@broadcom.com, rjw@rjwysocki.net,
        yi1.li@linux.intel.com, atull@kernel.org, moritz.fischer@ettus.com,
        pmladek@suse.com, johannes.berg@intel.com, emmanuel.grumbach@intel.com,
        luciano.coelho@intel.com, kvalo@codeaurora.org, luto@kernel.org,
        torvalds@linux-foundation.org, keescook@chromium.org,
        takahiro.akashi@linaro.org, dhowells@redhat.com, pjones@redhat.com,
        hdegoede@redhat.com, alan@linux.intel.com, tytso@mit.edu,
        paul.gortmaker@windriver.com, mtosatti@redhat.com,
        mawilcox@microsoft.com, linux-kernel@vger.kernel.org,
        "[4.10+]" <stable@vger.kernel.org>
Subject: Re: [PATCH v2] firmware: fix batched requests - wake all waiters
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 <20170626212312.31958-1-mcgrof@kernel.org>
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On Mon, Jun 26, 2017 at 02:23:12PM -0700, Luis R. Rodriguez wrote:
> From: Jakub Kicinski <jakub.kicinski@netronome.com>
> 
> 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@vger.kernel.org>    [4.10+]
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> [mcgrof: expanded on impact on commit log]
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> ---
> 
> 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?

thanks,

greg k-h