[PATCH]CFI fix of kernel deadlock caused by get_chip recursion

[Alexey Korolev]

Hi David,
> 
> I think the problem is probably pine sending 'format=flowed' text. That
> can be disabled. Please, remember to send patches to yourself _first_,
> then apply them from the mail you receive.
> 
> 
Yes you are right - the problem was in flowed format. Thank you very much!! The patch is double checked and must be Ok now. 

This patch solves kernel deadlock issue seen on JFFF2 simultaneous operations. 
Detailed investigation of the issue showed that the kernel deadlock is caused bytons of recursive get_chip calls.

MTD:CFI: This fix removes recursion in get_chip function to avoid possible deadlock situation.

Signed-off-by: Alexey Korolev <akorolev at infradead.org>
--------------------------
diff -aur a/drivers/mtd/chips/cfi_cmdset_0001.c b/drivers/mtd/chips/cfi_cmdset_0001.c
--- a/drivers/mtd/chips/cfi_cmdset_0001.c	2007-10-22 13:45:07.000000000 +0400
+++ b/drivers/mtd/chips/cfi_cmdset_0001.c	2007-10-22 17:34:34.000000000 +0400
@@ -85,6 +85,7 @@
 static void cfi_intelext_unpoint (struct mtd_info *mtd, u_char *addr, loff_t from,
 			size_t len);
 
+static int chip_ready (struct map_info *map, struct flchip *chip, unsigned long adr, int mode);
 static int get_chip(struct map_info *map, struct flchip *chip, unsigned long adr, int mode);
 static void put_chip(struct map_info *map, struct flchip *chip, unsigned long adr);
 #include "fwh_lock.h"
@@ -641,73 +642,13 @@
 /*
  *  *********** CHIP ACCESS FUNCTIONS ***********
  */
-
-static int get_chip(struct map_info *map, struct flchip *chip, unsigned long adr, int mode)
+static int chip_ready (struct map_info *map, struct flchip *chip, unsigned long adr, int mode)
 {
 	DECLARE_WAITQUEUE(wait, current);
 	struct cfi_private *cfi = map->fldrv_priv;
 	map_word status, status_OK = CMD(0x80), status_PWS = CMD(0x01);
-	unsigned long timeo;
 	struct cfi_pri_intelext *cfip = cfi->cmdset_priv;
-
- resettime:
-	timeo = jiffies + HZ;
- retry:
-	if (chip->priv && (mode == FL_WRITING || mode == FL_ERASING || mode == FL_OTP_WRITE || mode == FL_SHUTDOWN)) {
-		/*
-		 * OK. We have possibility for contension on the write/erase
-		 * operations which are global to the real chip and not per
-		 * partition.  So let's fight it over in the partition which
-		 * currently has authority on the operation.
-		 *
-		 * The rules are as follows:
-		 *
-		 * - any write operation must own shared->writing.
-		 *
-		 * - any erase operation must own _both_ shared->writing and
-		 *   shared->erasing.
-		 *
-		 * - contension arbitration is handled in the owner's context.
-		 *
-		 * The 'shared' struct can be read and/or written only when
-		 * its lock is taken.
-		 */
-		struct flchip_shared *shared = chip->priv;
-		struct flchip *contender;
-		spin_lock(&shared->lock);
-		contender = shared->writing;
-		if (contender && contender != chip) {
-			/*
-			 * The engine to perform desired operation on this
-			 * partition is already in use by someone else.
-			 * Let's fight over it in the context of the chip
-			 * currently using it.  If it is possible to suspend,
-			 * that other partition will do just that, otherwise
-			 * it'll happily send us to sleep.  In any case, when
-			 * get_chip returns success we're clear to go ahead.
-			 */
-			int ret = spin_trylock(contender->mutex);
-			spin_unlock(&shared->lock);
-			if (!ret)
-				goto retry;
-			spin_unlock(chip->mutex);
-			ret = get_chip(map, contender, contender->start, mode);
-			spin_lock(chip->mutex);
-			if (ret) {
-				spin_unlock(contender->mutex);
-				return ret;
-			}
-			timeo = jiffies + HZ;
-			spin_lock(&shared->lock);
-			spin_unlock(contender->mutex);
-		}
-
-		/* We now own it */
-		shared->writing = chip;
-		if (mode == FL_ERASING)
-			shared->erasing = chip;
-		spin_unlock(&shared->lock);
-	}
+	unsigned long timeo = jiffies + HZ;
 
 	switch (chip->state) {
 
@@ -722,16 +663,11 @@
 			if (chip->priv && map_word_andequal(map, status, status_PWS, status_PWS))
 				break;
 
-			if (time_after(jiffies, timeo)) {
-				printk(KERN_ERR "%s: Waiting for chip to be ready timed out. Status %lx\n",
-				       map->name, status.x[0]);
-				return -EIO;
-			}
 			spin_unlock(chip->mutex);
 			cfi_udelay(1);
 			spin_lock(chip->mutex);
 			/* Someone else might have been playing with it. */
-			goto retry;
+			return -EAGAIN;
 		}
 
 	case FL_READY:
@@ -809,8 +745,80 @@
 		schedule();
 		remove_wait_queue(&chip->wq, &wait);
 		spin_lock(chip->mutex);
-		goto resettime;
+		return -EAGAIN;
+	}
+}
+
+static int get_chip(struct map_info *map, struct flchip *chip, unsigned long adr, int mode)
+{
+	int ret;
+
+ retry:
+	if (chip->priv && (mode == FL_WRITING || mode == FL_ERASING || mode == FL_OTP_WRITE || mode == FL_SHUTDOWN)) {
+		/*
+		 * OK. We have possibility for contension on the write/erase
+		 * operations which are global to the real chip and not per
+		 * partition.  So let's fight it over in the partition which
+		 * currently has authority on the operation.
+		 *
+		 * The rules are as follows:
+		 *
+		 * - any write operation must own shared->writing.
+		 *
+		 * - any erase operation must own _both_ shared->writing and
+		 *   shared->erasing.
+		 *
+		 * - contension arbitration is handled in the owner's context.
+		 *
+		 * The 'shared' struct can be read and/or written only when
+		 * its lock is taken.
+		 */
+		struct flchip_shared *shared = chip->priv;
+		struct flchip *contender;
+		spin_lock(&shared->lock);
+		contender = shared->writing;
+		if (contender && contender != chip) {
+			/*
+			 * The engine to perform desired operation on this
+			 * partition is already in use by someone else.
+			 * Let's fight over it in the context of the chip
+			 * currently using it.  If it is possible to suspend,
+			 * that other partition will do just that, otherwise
+			 * 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);
+			spin_unlock(&shared->lock);
+			if (!ret)
+				goto retry;
+			spin_unlock(chip->mutex);
+			ret = chip_ready(map, contender, contender->start, mode);
+			spin_lock(chip->mutex);
+
+			if (ret == -EAGAIN) {
+				spin_unlock(contender->mutex);
+				goto retry;
+			}
+			if (ret) {
+				spin_unlock(contender->mutex);
+				return ret;
+			}
+			spin_lock(&shared->lock);
+			spin_unlock(contender->mutex);
+		}
+
+		/* We now own it */
+		shared->writing = chip;
+		if (mode == FL_ERASING)
+			shared->erasing = chip;
+		spin_unlock(&shared->lock);
 	}
+
+	ret = chip_ready(map, chip, adr, mode);
+	if (ret == -EAGAIN)
+		goto retry;
+
+	return ret;
 }
 
 static void put_chip(struct map_info *map, struct flchip *chip, unsigned long adr)