mtd: Add locking to cfi_cmdset_001:do_getlockstatus_oneblock

The function (do_getlockstatus_oneblock) switches the flash out of array-read mode and into query mode. It should not run in parallel to another function that uses array-read mode. We therefore need to acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).

I also assume that we should invalidate the cache in the same way that we do for do_otp_read.

Signed-off-by Mark Marshall <[email protected]>

---

Hi all,

We have had a device in production (and operation) for a long time running Linux and using a CFI NOR flash chip. We have recently started to get devices come back from the field with strange errors in the JFFS2 file system that is on this flash. It appeared that blocks of files on the image were being dropped (not flash blocks, just 4K sections from the middle of the files were being replaced with 0's).

After some debugging I found that sometimes, when the JFFS2 FS was reading the JFFS2 inode block it would get an CRC error. After adding some debug code I could see that in the error cases the "second half" of the read data was replaced with a fixed repeating pattern, and that this pattern was part of the CFI "QRY" data (It contained the flash manufacturer and device ID's).

This led me to think that maybe the problem was that some part of the MTD code was switching the device out of the normal "array-read" mode and into the query mode. After looking through the mtd code I found that the function 'do_getlockstatus_oneblock' does switch the mode of the flash without taking the chip mutex. Adding code to take the mutex has fixed our problem.

I am slightly surprised that no one else has seen this bug - the only thing I can think of is that reading the lock status of the flash is not something that happens in normal operation very often? We have a process on the device that generates a hardware check report at boot up, and one of the things that it does is report on the 'locked' status of the flash. This is always running while the JFFS2 code is performing it's initial scan.

The bug is fairly easy to reproduce if you have a system with the correct type of flash. In one terminal run something like:

while true ; do ( hd -n 65536 /dev/mtd0 | md5sum ) ; done

And in a second terminal run a program or utility that will check the lock status of the flash (mtdinfo should work). Assuming nothing else is writing to the flash partition mtd0 the md5sum will remain constant. When the bug bites you can see the md5sum change (but then recover).

Best Regards,

Mark Marshall

 drivers/mtd/chips/cfi_cmdset_0001.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

drivers/mtd/chips/cfi_cmdset_0001.c +19 -0

index 286b97a..d675efb 100644
@@ -2051,13 +2051,32 @@ static int __xipram
 do_getlockstatus_oneblock(struct map_info *map,
 {
 	struct cfi_private *cfi = map->fldrv_priv;
 	int status, ofs_factor = cfi->interleave * cfi->device_type;
+	int ret;
 
 	adr += chip->start;
+
+	mutex_lock(&chip->mutex);
+	ret = get_chip(map, chip, adr, FL_JEDEC_QUERY);
+	if (ret) {
+		mutex_unlock(&chip->mutex);
+		return ret;
+	}
+
+	/* let's ensure we're not reading back cached data from array mode */
+	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
 	xip_disable(map, chip, adr+(2*ofs_factor));
 	map_write(map, CMD(0x90), adr+(2*ofs_factor));
 	chip->state = FL_JEDEC_QUERY;
 	status = cfi_read_query(map, adr+(2*ofs_factor));
 	xip_enable(map, chip, 0);
+
+	/* then ensure we don't keep query data in the cache */
+	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
+	put_chip(map, chip, adr);
+	mutex_unlock(&chip->mutex);
+
 	return status;
 }

The function (do_getlockstatus_oneblock) switches the flash out of array-read mode and into query mode. It should not run in parallel to another function that uses array-read mode. We therefore need to acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).

 drivers/mtd/chips/cfi_cmdset_0001.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

drivers/mtd/chips/cfi_cmdset_0001.c +19 -0

index 286b97a..d675efb 100644
@@ -2051,13 +2051,32 @@ static int __xipram
 do_getlockstatus_oneblock(struct map_info *map,
 {
 > 	> struct cfi_private *cfi = map->fldrv_priv;
 > 	> int status, ofs_factor = cfi->interleave * cfi->device_type;
+> 	> int ret;
 
 > 	> adr += chip->start;
+
+> 	> mutex_lock(&chip->mutex);
+> 	> ret = get_chip(map, chip, adr, FL_JEDEC_QUERY);
+> 	> if (ret) {
+> 	> 	> mutex_unlock(&chip->mutex);
+> 	> 	> return ret;
+> 	> }
+
+> 	> /* let's ensure we're not reading back cached data from array mode */
+> 	> INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
 > 	> xip_disable(map, chip, adr+(2*ofs_factor));
 > 	> map_write(map, CMD(0x90), adr+(2*ofs_factor));
 > 	> chip->state = FL_JEDEC_QUERY;
 > 	> status = cfi_read_query(map, adr+(2*ofs_factor));
 > 	> xip_enable(map, chip, 0);
+
+> 	> /* then ensure we don't keep query data in the cache */
+> 	> INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
+> 	> put_chip(map, chip, adr);
+> 	> mutex_unlock(&chip->mutex);
+
 > 	> return status;
 }

Quoted 5 lines · Mark Marshall

The function (do_getlockstatus_oneblock) switches the flash out of array-read mode and into query mode. It should not run in parallel to another function that uses array-read mode. We therefore need to acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).

Hmm, this mail has NL breaks in it for long lines and won't apply. Is it on my end or yours?

From 49a50d75c7f4eed7a367d35f11afcdbd4573d193 Mon Sep 17 00:00:00 2001

Quoted 9 lines · Joakim Tjernlund

Quoted 5 lines · Mark Marshall

The function (do_getlockstatus_oneblock) switches the flash out of array-read mode and into query mode. It should not run in parallel to another function that uses array-read mode. We therefore need to acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).

Hmm, this mail has NL breaks in it for long lines and won't apply. Is it on my end or yours?

Sorry, it was on my end, here it is again.

From 49a50d75c7f4eed7a367d35f11afcdbd4573d193 Mon Sep 17 00:00:00 2001
From: Mark Marshall <[email protected]>
Date: Fri, 6 Nov 2015 14:09:49 +0100
Subject: [PATCH] mtd: Add locking to cfi_cmdset_001:do_getlockstatus_oneblock

The function (do_getlockstatus_oneblock) switches the flash out of array-read mode and into query mode. It should not run in parallel to another function that uses array-read mode. We therefore need to acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).

I also assume that we should invalidate the cache in the same way that we do for do_otp_read.

Signed-off-by Mark Marshall <[email protected]>

---

Hi all,

We have had a device in production (and operation) for a long time running Linux and using a CFI NOR flash chip. We have recently started to get devices come back from the field with strange errors in the JFFS2 file system that is on this flash. It appeared that blocks of files on the image were being dropped (not flash blocks, just 4K sections from the middle of the files were being replaced with 0's).

After some debugging I found that sometimes, when the JFFS2 FS was reading the JFFS2 inode block it would get an CRC error. After adding some debug code I could see that in the error cases the "second half" of the read data was replaced with a fixed repeating pattern, and that this pattern was part of the CFI "QRY" data (It contained the flash manufacturer and device ID's).

This led me to think that maybe the problem was that some part of the MTD code was switching the device out of the normal "array-read" mode and into the query mode. After looking through the mtd code I found that the function 'do_getlockstatus_oneblock' does switch the mode of the flash without taking the chip mutex. Adding code to take the mutex has fixed our problem.

I am slightly surprised that no one else has seen this bug - the only thing I can think of is that reading the lock status of the flash is not something that happens in normal operation very often? We have a process on the device that generates a hardware check report at boot up, and one of the things that it does is report on the 'locked' status of the flash. This is always running while the JFFS2 code is performing it's initial scan.

The bug is fairly easy to reproduce if you have a system with the correct type of flash. In one terminal run something like:

while true ; do ( hd -n 65536 /dev/mtd0 | md5sum ) ; done

And in a second terminal run a program or utility that will check the lock status of the flash (mtdinfo should work). Assuming nothing else is writing to the flash partition mtd0 the md5sum will remain constant. When the bug bites you can see the md5sum change (but then recover).

Best Regards,

Mark Marshall

(mark dot marshall at omicron dot at)

 drivers/mtd/chips/cfi_cmdset_0001.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

drivers/mtd/chips/cfi_cmdset_0001.c +19 -0

index 286b97a..d675efb 100644
@@ -2051,13 +2051,32 @@ static int __xipram do_getlockstatus_oneblock(struct map_info *map,
 {
 	struct cfi_private *cfi = map->fldrv_priv;
 	int status, ofs_factor = cfi->interleave * cfi->device_type;
+	int ret;
 
 	adr += chip->start;
+
+	mutex_lock(&chip->mutex);
+	ret = get_chip(map, chip, adr, FL_JEDEC_QUERY);
+	if (ret) {
+		mutex_unlock(&chip->mutex);
+		return ret;
+	}
+
+	/* let's ensure we're not reading back cached data from array mode */
+	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
 	xip_disable(map, chip, adr+(2*ofs_factor));
 	map_write(map, CMD(0x90), adr+(2*ofs_factor));
 	chip->state = FL_JEDEC_QUERY;
 	status = cfi_read_query(map, adr+(2*ofs_factor));
 	xip_enable(map, chip, 0);
+
+	/* then ensure we don't keep query data in the cache */
+	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
+
+	put_chip(map, chip, adr);
+	mutex_unlock(&chip->mutex);
+
 	return status;
 }