linux-kernel - Re: [PATCH V2] mmc: sdhci: don't read cd-gpio while holding spinlock

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Date:	Mon, 24 Mar 2014 09:18:02 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Chris Ball <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] mmc: sdhci: don't read cd-gpio while holding spinlock

On Sun, Mar 23, 2014 at 11:19 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 24.03.2014 03:43, Andrew Bresticker wrote:
>> sdhci_request() and sdhci_card_event() read the cd-gpio via
>> mmc_gpio_get_cd(), which can sleep, while holding host->lock.
>> This may result in the following BUG:
>>
>>   BUG: spinlock wrong CPU on CPU#2, kworker/u8:16/4296
>>   lock: 0xea6b9c80, .magic: dead4ead, .owner: kworker/u8:16/4296, .owner_cpu: 0
>>   CPU: 2 PID: 4296 Comm: kworker/u8:16 Tainted: G         C   3.10.18 #137
>>   Workqueue: kmmcd mmc_rescan
>>   [<8020cf8c>] (unwind_backtrace+0x0/0x118) from [<8020a0c8>] (show_stack+0x20/0x24)
>>   [<8020a0c8>] (show_stack+0x20/0x24) from [<8075e5b8>] (dump_stack+0x20/0x28)
>>   [<8075e5b8>] (dump_stack+0x20/0x28) from [<804184a8>] (spin_dump+0x80/0x94)
>>   [<804184a8>] (spin_dump+0x80/0x94) from [<804184e8>] (spin_bug+0x2c/0x30)
>>   [<804184e8>] (spin_bug+0x2c/0x30) from [<80418790>] (do_raw_spin_unlock+0x94/0xd4)
>>   [<80418790>] (do_raw_spin_unlock+0x94/0xd4) from [<80761a44>] (_raw_spin_unlock_irqrestore+0x1c/0x24)
>>   [<80761a44>] (_raw_spin_unlock_irqrestore+0x1c/0x24) from [<805ff66c>] (sdhci_request+0x1c8/0x1d0)
>>   [<805ff66c>] (sdhci_request+0x1c8/0x1d0) from [<805ebb5c>] (mmc_start_request+0xec/0xf4)
>>   [<805ebb5c>] (mmc_start_request+0xec/0xf4) from [<805ebcbc>] (mmc_wait_for_req+0x80/0xf4)
>>   ...
>>
>> Read the cd-gpio before acquiring the spinlock instead.
>>
>> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
>> ---
>>  drivers/mmc/host/sdhci.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 04a5e25..328b250 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -1340,6 +1340,7 @@ static void sdhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>>       u32 tuning_opcode;
>>
>>       host = mmc_priv(mmc);
>> +     present = mmc_gpio_get_cd(host->mmc);
>>
>>       sdhci_runtime_pm_get(host);
>>
>> @@ -1371,7 +1372,6 @@ static void sdhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>>        *     zero: cd-gpio is used, and card is removed
>>        *     one: cd-gpio is used, and card is present
>>        */
>> -     present = mmc_gpio_get_cd(host->mmc);
>>       if (present < 0) {
>>               /* If polling, assume that the card is always present. */
>>               if (host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION)
>> @@ -2082,15 +2082,16 @@ static void sdhci_card_event(struct mmc_host *mmc)
>>  {
>>       struct sdhci_host *host = mmc_priv(mmc);
>>       unsigned long flags;
>> +     int present;
>>
>>       /* First check if client has provided their own card event */
>>       if (host->ops->card_event)
>>               host->ops->card_event(host);
>>
>> +     present = sdhci_get_cd(mmc);
>
> Shouldn't that be sdhci_do_get_cd(mmc) ?

No I do mean shdic_get_cd().  We might be runtime suspended so we need
sdhci_get_cd() to increment the device usage count and do a runtime
resume if necessary.

>
>>       spin_lock_irqsave(&host->lock, flags);
>>
>> -     /* Check host->mrq first in case we are runtime suspended */
>> -     if (host->mrq && !sdhci_do_get_cd(host)) {
>> +     if (host->mrq && !present) {
>>               pr_err("%s: Card removed during transfer!\n",
>>                       mmc_hostname(host->mmc));
>>               pr_err("%s: Resetting controller.\n",
>>
>
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