On Sunday, 24 of February 2008, Alan Stern wrote:
> On Sat, 23 Feb 2008, Alan Stern wrote:
>
> > It happened in a workqueue. There could be lots of similar cases: Some
> > interrupt-driven event causes a hotplug action. Since the action can't
> > be carried out in interrupt context, the driver has no choice but to
> > defer it to a workqueue or kernel thread. Blocking that workqueue or
> > kernel thread won't cause a problem _unless_ the driver's
> > suspend/resume methods try to synchronize with it. That's the
> > difficult case.
>
> In fact this turns out to be exactly the problem with the MMC
> subsystem. It uses a dedicated workqueue (kmmcd) to handle state
> changes, and mmc_suspend_host() does a flush_workqueue(). If the
> workqueue contains an entry to register or unregister a device, this is
> guaranteed to deadlock -- and that's exactly what happens when Zdenek
> inserts or removes a card during the disk-drive spindown time of a
> system sleep.
>
> It looks like the best solution is for mmc_suspend_host() not to flush
> the workqueue; instead the workqueue should prevent itself from
> running during a suspend. Right now the easiest way to accomplish this
> is for the workqueue routines (mmc_detect() and siblings) to acquire
> the mmc_host's device semaphore. If in the future the MMC subsystem
> adds dynamic PM support then a more complicated arrangement will be
> needed.
>
> So the patch below, in combination with the previous patch, might just
> fix the whole problem.
The patch looks sane and I think you're right.
Still, it depends on us holding the device semaphores (if I understand it
correctly). For this reason, I'd prefer to include it into the patch that adds
device locking to the PM core.
I think we should first remove the device locking from
drivers/base/power/main.c (that's the patch I'd like to push upstream now) and
then create a patch that will add it back along with all of the necessary
additional changes we know of (BTW, I've just received a message from another
user affected by it).
but we need to be careful with
all the details. IMO, it would be
Thanks,
Rafael
> Index: usb-2.6/drivers/mmc/core/core.c
> ===================================================================
> --- usb-2.6.orig/drivers/mmc/core/core.c
> +++ usb-2.6/drivers/mmc/core/core.c
> @@ -731,8 +731,6 @@ void mmc_stop_host(struct mmc_host *host
> */
> int mmc_suspend_host(struct mmc_host *host, pm_message_t state)
> {
> - mmc_flush_scheduled_work();
> -
> mmc_bus_get(host);
> if (host->bus_ops && !host->bus_dead) {
> if (host->bus_ops->suspend)
> Index: usb-2.6/drivers/mmc/core/mmc.c
> ===================================================================
> --- usb-2.6.orig/drivers/mmc/core/mmc.c
> +++ usb-2.6/drivers/mmc/core/mmc.c
> @@ -441,6 +441,7 @@ static void mmc_detect(struct mmc_host *
> BUG_ON(!host);
> BUG_ON(!host->card);
>
> + down(&mmc_classdev(host)->sem);
> mmc_claim_host(host);
>
> /*
> @@ -449,6 +450,7 @@ static void mmc_detect(struct mmc_host *
> err = mmc_send_status(host->card, NULL);
>
> mmc_release_host(host);
> + up(&mmc_classdev(host)->sem);
>
> if (err) {
> mmc_remove(host);
> Index: usb-2.6/drivers/mmc/core/sd.c
> ===================================================================
> --- usb-2.6.orig/drivers/mmc/core/sd.c
> +++ usb-2.6/drivers/mmc/core/sd.c
> @@ -500,6 +500,7 @@ static void mmc_sd_detect(struct mmc_hos
> BUG_ON(!host);
> BUG_ON(!host->card);
>
> + down(&mmc_classdev(host)->sem);
> mmc_claim_host(host);
>
> /*
> @@ -508,6 +509,7 @@ static void mmc_sd_detect(struct mmc_hos
> err = mmc_send_status(host->card, NULL);
>
> mmc_release_host(host);
> + up(&mmc_classdev(host)->sem);
>
> if (err) {
> mmc_sd_remove(host);
> Index: usb-2.6/drivers/mmc/core/sdio.c
> ===================================================================
> --- usb-2.6.orig/drivers/mmc/core/sdio.c
> +++ usb-2.6/drivers/mmc/core/sdio.c
> @@ -195,6 +195,7 @@ static void mmc_sdio_detect(struct mmc_h
> BUG_ON(!host);
> BUG_ON(!host->card);
>
> + down(&mmc_classdev(host)->sem);
> mmc_claim_host(host);
>
> /*
> @@ -203,6 +204,7 @@ static void mmc_sdio_detect(struct mmc_h
> err = mmc_select_card(host->card);
>
> mmc_release_host(host);
> + up(&mmc_classdev(host)->sem);
>
> if (err) {
> mmc_sdio_remove(host);
>
>
>
--
"Premature optimization is the root of all evil." - Donald Knuth
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