From: Doug Anderson <dianders@chromium.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Linux MMC List <linux-mmc@vger.kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Brian Norris <briannorris@chromium.org>,
Shawn Lin <shawn.lin@rock-chips.com>,
Guenter Roeck <groeck@chromium.org>,
Heiko Stuebner <heiko@sntech.de>,
Kalle Valo <kvalo@codeaurora.org>,
linux-wireless <linux-wireless@vger.kernel.org>,
"# 4.0+" <stable@vger.kernel.org>
Subject: Re: [PATCH] mmc: core: Prevent processing SDIO IRQs when the card is suspended
Date: Fri, 14 Jun 2019 08:41:58 -0700 [thread overview]
Message-ID: <CAD=FV=Ujb=_jEFMdxLPW6tYwb9DZo5-RZ8BVuyq5DdFQ5jJbQw@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFpqk4ZcVTqifnbnW1WgNfx9ZNebCttUPcK_e9KWqpDMjQ@mail.gmail.com>
Hi,
On Fri, Jun 14, 2019 at 4:56 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> > I was more worried about the safety of mmc_card_set_suspended()
> > itself. That is:
> >
> > #define mmc_card_set_suspended(c) ((c)->state |= MMC_STATE_SUSPENDED)
> >
> > ...so it's doing a read-modify-write of "state". Is that safe to do
> > without any type of locking?
>
> In this case, yes I think so.
>
> The point is, it really doesn't matter if the reader (work or thread),
> reads a non-updated value, because the synchronization is managed by
> the later mmc_claim_host() and the cancel_delayed_work_sync().
If this were just an "int" then perhaps, but this is a bitfield. So
if someone else updates the bitfield at the same time then we can
fully clobber their modification or they can clobber ours, right?
task 1: load "state" from memory into CPU register on cpu0
task 2: load "state" from memory into CPU register on cpu1
task 1: OR in MMC_CARD_REMOVED
task 1: write "state" from CPU register on cpu0
task 2: OR in MMC_STATE_SUSPENDED
task 2: write "state" from CPU register on cpu1
...so now we've clobbered MMC_CARD_REMOVED. ...or am I just being
paranoid here and everything else in "state" is somehow guaranteed to
not be touched at the same time this function is running?
-Doug
next prev parent reply other threads:[~2019-06-14 15:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-11 12:32 [PATCH] mmc: core: Prevent processing SDIO IRQs when the card is suspended Ulf Hansson
2019-06-12 22:20 ` Doug Anderson
2019-06-12 22:20 ` Doug Anderson
2019-06-13 9:29 ` Ulf Hansson
2019-06-13 18:05 ` Doug Anderson
2019-06-14 11:55 ` Ulf Hansson
2019-06-14 15:41 ` Doug Anderson [this message]
2019-06-17 9:56 ` Ulf Hansson
2019-08-12 18:39 ` Matthias Kaehlcke
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