Re: [PATCH 26/32] omap_hsmmc: prevent races with irq handler

Adrian Hunter
2009-07-27T09:06:37Z

Andrew Morton wrote:
> On Fri, 10 Jul 2009 15:43:09 +0300
> Adrian Hunter <adrian.hunter@nokia.com> wrote:
>
>> >From 242fae6293adec671b14354f215217354f5076a0 Mon Sep 17 00:00:00 2001
>> From: Adrian Hunter <adrian.hunter@nokia.com>
>> Date: Sat, 16 May 2009 10:32:34 +0300
>> Subject: [PATCH] omap_hsmmc: prevent races with irq handler
>>
>> If an unexpected interrupt occurs while preparing the
>> next request, an oops can occur.
>>
>> For example, a new request is setting up DMA for data
>> transfer so host->data is not NULL. An unexpected
>> transfer complete (TC) interrupt comes along and
>> the interrupt handler sets host->data to NULL. Oops!
>>
>> Prevent that by disabling interrupts while setting up
>> a new request.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
>> ---
>> drivers/mmc/host/omap_hsmmc.c | 16 ++++++++++++++++
>> 1 files changed, 16 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
>> index 28563d6..38e1410 100644
>> --- a/drivers/mmc/host/omap_hsmmc.c
>> +++ b/drivers/mmc/host/omap_hsmmc.c
>> @@ -452,6 +452,13 @@ mmc_omap_start_command(struct mmc_omap_host *host, struct mmc_command *cmd,
>> if (host->use_dma)
>> cmdreg |= DMA_EN;
>>
>> + /*
>> + * In an interrupt context (i.e. STOP command), the interrupt is already
>> + * enabled, otherwise it is not (i.e. new request).
>> + */
>> + if (!in_interrupt())
>> + enable_irq(host->irq);
>> +
>> OMAP_HSMMC_WRITE(host->base, ARG, cmd->arg);
>> OMAP_HSMMC_WRITE(host->base, CMD, cmdreg);
>> }
>> @@ -1011,6 +1018,13 @@ static void omap_mmc_request(struct mmc_host *mmc, struct mmc_request *req)
>> struct mmc_omap_host *host = mmc_priv(mmc);
>> int err;
>>
>> + /*
>> + * Prevent races with the interrupt handler because of unexpected
>> + * interrupts, but not if we are already in interrupt context i.e.
>> + * retries.
>> + */
>> + if (!in_interrupt())
>> + disable_irq(host->irq);
>> WARN_ON(host->mrq != NULL);
>> host->mrq = req;
>> err = mmc_omap_prepare_data(host, req);
>> @@ -1019,6 +1033,8 @@ static void omap_mmc_request(struct mmc_host *mmc, struct mmc_request *req)
>> if (req->data)
>> req->data->error = err;
>> host->mrq = NULL;
>> + if (!in_interrupt())
>> + enable_irq(host->irq);
>> mmc_request_done(mmc, req);
>> return;
>> }
>
> That seems pretty crude. Disabling an interrupt line can be expensive,
> and will shut off any other innocent devices which share the line.
>
> The usual and superior way of fixing races such as this is
> spin_lock_irq[save]().
>
>

>From f54be3678907b85a00d9f51e3ce4c828fc21ee95 Mon Sep 17 00:00:00 2001
From: Adrian Hunter <adrian.hunter@nokia.com>
Date: Mon, 27 Jul 2009 12:00:17 +0300
Subject: [PATCH] omap_hsmmc: use spin_lock not disable_irq

Disabling an interrupt line can be expensive. The usual and
superior way of fixing races such as this is spin_lock_irqsave.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
---
drivers/mmc/host/omap_hsmmc.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index 8900bae..9850280 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -146,6 +146,8 @@ struct omap_hsmmc_host {
struct work_struct mmc_carddetect_work;
void __iomem *base;
resource_size_t mapbase;
+ spinlock_t irq_lock;
+ unsigned long flags;
unsigned int id;
unsigned int dma_len;
unsigned int dma_sg_idx;
@@ -462,7 +464,7 @@ omap_hsmmc_start_command(struct omap_hsmmc_host *host, struct mmc_command *cmd,
* enabled, otherwise it is not (i.e. new request).
*/
if (!in_interrupt())
- enable_irq(host->irq);
+ spin_unlock_irqrestore(&host->irq_lock, host->flags);

OMAP_HSMMC_WRITE(host->base, ARG, cmd->arg);
OMAP_HSMMC_WRITE(host->base, CMD, cmdreg);
@@ -626,11 +628,14 @@ static irqreturn_t omap_hsmmc_irq(int irq, void *dev_id)
struct mmc_data *data;
int end_cmd = 0, end_trans = 0, status;

+ spin_lock(&host->irq_lock);
+
if (host->mrq == NULL) {
OMAP_HSMMC_WRITE(host->base, STAT,
OMAP_HSMMC_READ(host->base, STAT));
/* Flush posted write */
OMAP_HSMMC_READ(host->base, STAT);
+ spin_unlock(&host->irq_lock);
return IRQ_HANDLED;
}

@@ -696,6 +701,8 @@ static irqreturn_t omap_hsmmc_irq(int irq, void *dev_id)
if ((end_trans || (status & TC)) && host->mrq)
omap_hsmmc_xfer_done(host, data);

+ spin_unlock(&host->irq_lock);
+
return IRQ_HANDLED;
}

@@ -1066,7 +1073,7 @@ static void omap_hsmmc_request(struct mmc_host *mmc, struct mmc_request *req)
* retries.
*/
if (!in_interrupt()) {
- disable_irq(host->irq);
+ spin_lock_irqsave(&host->irq_lock, host->flags);
/*
* Protect the card from I/O if there is a possibility
* it can be removed.
@@ -1085,7 +1092,7 @@ static void omap_hsmmc_request(struct mmc_host *mmc, struct mmc_request *req)
req->cmd->error = -EBADF;
if (req->data)
req->data->error = -EBADF;
- enable_irq(host->irq);
+ spin_unlock_irqrestore(&host->irq_lock, host->flags);
mmc_request_done(mmc, req);
return;
} else if (host->reqs_blocked)
@@ -1100,7 +1107,7 @@ static void omap_hsmmc_request(struct mmc_host *mmc, struct mmc_request *req)
req->data->error = err;
host->mrq = NULL;
if (!in_interrupt())
- enable_irq(host->irq);
+ spin_unlock_irqrestore(&host->irq_lock, host->flags);
mmc_request_done(mmc, req);
return;
}
@@ -1653,6 +1660,7 @@ static int __init omap_hsmmc_probe(struct platform_device *pdev)
mmc->f_max = 52000000;

sema_init(&host->sem, 1);
+ spin_lock_init(&host->irq_lock);

host->iclk = clk_get(&pdev->dev, "ick");
if (IS_ERR(host->iclk)) {
--
1.5.6.3