mtd: fix a huge latency problem in the MTD CFI and LPDDR flash drivers.

The use of a memcpy() during a spinlock operation will cause very long
thread context switch delays if the flash chip bandwidth is low and the
data to be copied large, because a spinlock will disable preemption.

For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
which request sometimes 128 KiB (the flash erase size), a preemption delay of
20 milliseconds. High priority threads will not be served during this
time, regardless whether this threads access the flash or not. This behavior
breaks real time.

The patch changes all the use of spin_lock operations for xxxx->mutex
into mutex operations, which is exact what the name says and means.

I have checked the code of the drivers and there is no use of atomic
pathes like interrupt or timers. The mtdoops facility will also not be used
by this drivers. So it is dave to replace the spin_lock against mutex.

There is no performance regression since the mutex is normally not
acquired.

Changelog:
 06.03.2010 First release
 26.03.2010 Fix mutex[1] issue and tested it for compile failure
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/chips/fwh_lock.h

@@ -58,10 +58,10 @@ static int fwh_xxlock_oneblock(struct map_info *map, struct flchip *chip,
 	 * to flash memory - that means that we don't have to check status
 	 * and timeout.
 	 */
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, adr, FL_LOCKING);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 
@@ -72,7 +72,7 @@ static int fwh_xxlock_oneblock(struct map_info *map, struct flchip *chip,
 	/* Done and happy. */
 	chip->state = chip->oldstate;
 	put_chip(map, chip, adr);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return 0;
 }
 

drivers/mtd/chips/gen_probe.c

@@ -155,8 +155,7 @@ static struct cfi_private *genprobe_ident_chips(struct map_info *map, struct chi
 			pchip->start = (i << cfi.chipshift);
 			pchip->state = FL_READY;
 			init_waitqueue_head(&pchip->wq);
-			spin_lock_init(&pchip->_spinlock);
-			pchip->mutex = &pchip->_spinlock;
+			mutex_init(&pchip->mutex);
 		}
 	}
 

drivers/mtd/lpddr/lpddr_cmds.c

@@ -106,8 +106,7 @@ struct mtd_info *lpddr_cmdset(struct map_info *map)
 			/* those should be reset too since
 			   they create memory references. */
 			init_waitqueue_head(&chip->wq);
-			spin_lock_init(&chip->_spinlock);
-			chip->mutex = &chip->_spinlock;
+			mutex_init(&chip->mutex);
 			chip++;
 		}
 	}
@@ -143,7 +142,7 @@ static int wait_for_ready(struct map_info *map, struct flchip *chip,
 		}
 
 		/* OK Still waiting. Drop the lock, wait a while and retry. */
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		if (sleep_time >= 1000000/HZ) {
 			/*
 			 * Half of the normal delay still remaining
@@ -158,17 +157,17 @@ static int wait_for_ready(struct map_info *map, struct flchip *chip,
 			cond_resched();
 			timeo--;
 		}
-		spin_lock(chip->mutex);
+		mutex_lock(&chip->mutex);
 
 		while (chip->state != chip_state) {
 			/* Someone's suspended the operation: sleep */
 			DECLARE_WAITQUEUE(wait, current);
 			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
-			spin_unlock(chip->mutex);
+			mutex_unlock(&chip->mutex);
 			schedule();
 			remove_wait_queue(&chip->wq, &wait);
-			spin_lock(chip->mutex);
+			mutex_lock(&chip->mutex);
 		}
 		if (chip->erase_suspended || chip->write_suspended)  {
 			/* Suspend has occured while sleep: reset timeout */
@@ -229,20 +228,20 @@ static int get_chip(struct map_info *map, struct flchip *chip, int mode)
 			 * it'll happily send us to sleep.  In any case, when
 			 * get_chip returns success we're clear to go ahead.
 			 */
-			ret = spin_trylock(contender->mutex);
+			ret = mutex_trylock(&contender->mutex);
 			spin_unlock(&shared->lock);
 			if (!ret)
 				goto retry;
-			spin_unlock(chip->mutex);
+			mutex_unlock(&chip->mutex);
 			ret = chip_ready(map, contender, mode);
-			spin_lock(chip->mutex);
+			mutex_lock(&chip->mutex);
 
 			if (ret == -EAGAIN) {
-				spin_unlock(contender->mutex);
+				mutex_unlock(&contender->mutex);
 				goto retry;
 			}
 			if (ret) {
-				spin_unlock(contender->mutex);
+				mutex_unlock(&contender->mutex);
 				return ret;
 			}
 			spin_lock(&shared->lock);
@@ -251,10 +250,10 @@ static int get_chip(struct map_info *map, struct flchip *chip, int mode)
 			 * state. Put contender and retry. */
 			if (chip->state == FL_SYNCING) {
 				put_chip(map, contender);
-				spin_unlock(contender->mutex);
+				mutex_unlock(&contender->mutex);
 				goto retry;
 			}
-			spin_unlock(contender->mutex);
+			mutex_unlock(&contender->mutex);
 		}
 
 		/* Check if we have suspended erase on this chip.
@@ -264,10 +263,10 @@ static int get_chip(struct map_info *map, struct flchip *chip, int mode)
 			spin_unlock(&shared->lock);
 			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
-			spin_unlock(chip->mutex);
+			mutex_unlock(&chip->mutex);
 			schedule();
 			remove_wait_queue(&chip->wq, &wait);
-			spin_lock(chip->mutex);
+			mutex_lock(&chip->mutex);
 			goto retry;
 		}
 
@@ -336,10 +335,10 @@ static int chip_ready(struct map_info *map, struct flchip *chip, int mode)
 sleep:
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		add_wait_queue(&chip->wq, &wait);
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		schedule();
 		remove_wait_queue(&chip->wq, &wait);
-		spin_lock(chip->mutex);
+		mutex_lock(&chip->mutex);
 		return -EAGAIN;
 	}
 }
@@ -355,12 +354,12 @@ static void put_chip(struct map_info *map, struct flchip *chip)
 			if (shared->writing && shared->writing != chip) {
 				/* give back the ownership */
 				struct flchip *loaner = shared->writing;
-				spin_lock(loaner->mutex);
+				mutex_lock(&loaner->mutex);
 				spin_unlock(&shared->lock);
-				spin_unlock(chip->mutex);
+				mutex_unlock(&chip->mutex);
 				put_chip(map, loaner);
-				spin_lock(chip->mutex);
-				spin_unlock(loaner->mutex);
+				mutex_lock(&chip->mutex);
+				mutex_unlock(&loaner->mutex);
 				wake_up(&chip->wq);
 				return;
 			}
@@ -413,10 +412,10 @@ int do_write_buffer(struct map_info *map, struct flchip *chip,
 
 	wbufsize = 1 << lpddr->qinfo->BufSizeShift;
 
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, FL_WRITING);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 	/* Figure out the number of words to write */
@@ -477,7 +476,7 @@ int do_write_buffer(struct map_info *map, struct flchip *chip,
 	}
 
  out:	put_chip(map, chip);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return ret;
 }
 
@@ -489,10 +488,10 @@ int do_erase_oneblock(struct mtd_info *mtd, loff_t adr)
 	struct flchip *chip = &lpddr->chips[chipnum];
 	int ret;
 
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, FL_ERASING);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 	send_pfow_command(map, LPDDR_BLOCK_ERASE, adr, 0, NULL);
@@ -504,7 +503,7 @@ int do_erase_oneblock(struct mtd_info *mtd, loff_t adr)
 		goto out;
 	}
  out:	put_chip(map, chip);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return ret;
 }
 
@@ -517,10 +516,10 @@ static int lpddr_read(struct mtd_info *mtd, loff_t adr, size_t len,
 	struct flchip *chip = &lpddr->chips[chipnum];
 	int ret = 0;
 
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, FL_READY);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 
@@ -528,7 +527,7 @@ static int lpddr_read(struct mtd_info *mtd, loff_t adr, size_t len,
 	*retlen = len;
 
 	put_chip(map, chip);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return ret;
 }
 
@@ -568,9 +567,9 @@ static int lpddr_point(struct mtd_info *mtd, loff_t adr, size_t len,
 		else
 			thislen = len;
 		/* get the chip */
-		spin_lock(chip->mutex);
+		mutex_lock(&chip->mutex);
 		ret = get_chip(map, chip, FL_POINT);
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		if (ret)
 			break;
 
@@ -610,7 +609,7 @@ static void lpddr_unpoint (struct mtd_info *mtd, loff_t adr, size_t len)
 		else
 			thislen = len;
 
-		spin_lock(chip->mutex);
+		mutex_lock(&chip->mutex);
 		if (chip->state == FL_POINT) {
 			chip->ref_point_counter--;
 			if (chip->ref_point_counter == 0)
@@ -620,7 +619,7 @@ static void lpddr_unpoint (struct mtd_info *mtd, loff_t adr, size_t len)
 					"pointed region\n", map->name);
 
 		put_chip(map, chip);
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 
 		len -= thislen;
 		ofs = 0;
@@ -726,10 +725,10 @@ int do_xxlock(struct mtd_info *mtd, loff_t adr, uint32_t len, int thunk)
 	int chipnum = adr >> lpddr->chipshift;
 	struct flchip *chip = &lpddr->chips[chipnum];
 
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, FL_LOCKING);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 
@@ -749,7 +748,7 @@ int do_xxlock(struct mtd_info *mtd, loff_t adr, uint32_t len, int thunk)
 		goto out;
 	}
 out:	put_chip(map, chip);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return ret;
 }
 
@@ -770,10 +769,10 @@ int word_program(struct map_info *map, loff_t adr, uint32_t curval)
 	int chipnum = adr >> lpddr->chipshift;
 	struct flchip *chip = &lpddr->chips[chipnum];
 
-	spin_lock(chip->mutex);
+	mutex_lock(&chip->mutex);
 	ret = get_chip(map, chip, FL_WRITING);
 	if (ret) {
-		spin_unlock(chip->mutex);
+		mutex_unlock(&chip->mutex);
 		return ret;
 	}
 
@@ -787,7 +786,7 @@ int word_program(struct map_info *map, loff_t adr, uint32_t curval)
 	}
 
 out:	put_chip(map, chip);
-	spin_unlock(chip->mutex);
+	mutex_unlock(&chip->mutex);
 	return ret;
 }
 

include/linux/mtd/flashchip.h

@@ -15,6 +15,7 @@
  * has asm/spinlock.h, or 2.4, which has linux/spinlock.h
  */
 #include <linux/sched.h>
+#include <linux/mutex.h>
 
 typedef enum {
 	FL_READY,
@@ -74,8 +75,7 @@ struct flchip {
 	unsigned int erase_suspended:1;
 	unsigned long in_progress_block_addr;
 
-	spinlock_t *mutex;
-	spinlock_t _spinlock; /* We do it like this because sometimes they'll be shared. */
+	struct mutex mutex;
 	wait_queue_head_t wq; /* Wait on here when we're waiting for the chip
 			     to be ready */
 	int word_write_time;