mmc: protect the tmio_mmc driver against a theoretical race
Guennadi Liakhovetski [Thu, 21 Apr 2011 07:20:16 +0000 (07:20 +0000)]
The MMC subsystem does not guarantee, that host driver .request() and
.set_ios() callbacks are serialised. Such concurrent calls, however,
do not have to be meaningfully supported, drivers just have to make
sure to avoid any severe problems.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/tmio_mmc.h
drivers/mmc/host/tmio_mmc_pio.c

index c1470e6..58138a2 100644 (file)
@@ -19,6 +19,7 @@
 #include <linux/highmem.h>
 #include <linux/mmc/tmio.h>
 #include <linux/pagemap.h>
+#include <linux/spinlock.h>
 
 /* Definitions for values the CTRL_SDIO_STATUS register can take. */
 #define TMIO_SDIO_STAT_IOIRQ   0x0001
index 8b05d3c..ea6ade3 100644 (file)
@@ -244,8 +244,12 @@ static void tmio_mmc_reset_work(struct work_struct *work)
        spin_lock_irqsave(&host->lock, flags);
        mrq = host->mrq;
 
-       /* request already finished */
-       if (!mrq
+       /*
+        * is request already finished? Since we use a non-blocking
+        * cancel_delayed_work(), it can happen, that a .set_ios() call preempts
+        * us, so, have to check for IS_ERR(host->mrq)
+        */
+       if (IS_ERR_OR_NULL(mrq)
            || time_is_after_jiffies(host->last_req_ts +
                msecs_to_jiffies(2000))) {
                spin_unlock_irqrestore(&host->lock, flags);
@@ -265,16 +269,19 @@ static void tmio_mmc_reset_work(struct work_struct *work)
 
        host->cmd = NULL;
        host->data = NULL;
-       host->mrq = NULL;
        host->force_pio = false;
 
        spin_unlock_irqrestore(&host->lock, flags);
 
        tmio_mmc_reset(host);
 
+       /* Ready for new calls */
+       host->mrq = NULL;
+
        mmc_request_done(host->mmc, mrq);
 }
 
+/* called with host->lock held, interrupts disabled */
 static void tmio_mmc_finish_request(struct tmio_mmc_host *host)
 {
        struct mmc_request *mrq = host->mrq;
@@ -282,13 +289,15 @@ static void tmio_mmc_finish_request(struct tmio_mmc_host *host)
        if (!mrq)
                return;
 
-       host->mrq = NULL;
        host->cmd = NULL;
        host->data = NULL;
        host->force_pio = false;
 
        cancel_delayed_work(&host->delayed_reset_work);
 
+       host->mrq = NULL;
+
+       /* FIXME: mmc_request_done() can schedule! */
        mmc_request_done(host->mmc, mrq);
 }
 
@@ -686,15 +695,27 @@ static int tmio_mmc_start_data(struct tmio_mmc_host *host,
 static void tmio_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
 {
        struct tmio_mmc_host *host = mmc_priv(mmc);
+       unsigned long flags;
        int ret;
 
-       if (host->mrq)
+       spin_lock_irqsave(&host->lock, flags);
+
+       if (host->mrq) {
                pr_debug("request not null\n");
+               if (IS_ERR(host->mrq)) {
+                       spin_unlock_irqrestore(&host->lock, flags);
+                       mrq->cmd->error = -EAGAIN;
+                       mmc_request_done(mmc, mrq);
+                       return;
+               }
+       }
 
        host->last_req_ts = jiffies;
        wmb();
        host->mrq = mrq;
 
+       spin_unlock_irqrestore(&host->lock, flags);
+
        if (mrq->data) {
                ret = tmio_mmc_start_data(host, mrq->data);
                if (ret)
@@ -709,8 +730,8 @@ static void tmio_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
        }
 
 fail:
-       host->mrq = NULL;
        host->force_pio = false;
+       host->mrq = NULL;
        mrq->cmd->error = ret;
        mmc_request_done(mmc, mrq);
 }
@@ -724,6 +745,29 @@ fail:
 static void tmio_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 {
        struct tmio_mmc_host *host = mmc_priv(mmc);
+       unsigned long flags;
+
+       spin_lock_irqsave(&host->lock, flags);
+       if (host->mrq) {
+               if (IS_ERR(host->mrq)) {
+                       dev_dbg(&host->pdev->dev,
+                               "%s.%d: concurrent .set_ios(), clk %u, mode %u\n",
+                               current->comm, task_pid_nr(current),
+                               ios->clock, ios->power_mode);
+                       host->mrq = ERR_PTR(-EINTR);
+               } else {
+                       dev_dbg(&host->pdev->dev,
+                               "%s.%d: CMD%u active since %lu, now %lu!\n",
+                               current->comm, task_pid_nr(current),
+                               host->mrq->cmd->opcode, host->last_req_ts, jiffies);
+               }
+               spin_unlock_irqrestore(&host->lock, flags);
+               return;
+       }
+
+       host->mrq = ERR_PTR(-EBUSY);
+
+       spin_unlock_irqrestore(&host->lock, flags);
 
        if (ios->clock)
                tmio_mmc_set_clock(host, ios->clock);
@@ -754,6 +798,12 @@ static void tmio_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 
        /* Let things settle. delay taken from winCE driver */
        udelay(140);
+       if (PTR_ERR(host->mrq) == -EINTR)
+               dev_dbg(&host->pdev->dev,
+                       "%s.%d: IOS interrupted: clk %u, mode %u",
+                       current->comm, task_pid_nr(current),
+                       ios->clock, ios->power_mode);
+       host->mrq = NULL;
 }
 
 static int tmio_mmc_get_ro(struct mmc_host *mmc)