Bad Blocks On JFFS2/NAND

I have experienced a problem in which a JFF2 filesystem on NAND became full. This is a root file system and constant writes to a logfile filled the filesystem. On investigation it was found that the NAND device now had hundreds of bad blocks.

I started to investigate this and found that JFFS2 was announcing

Newly-erased block contained word 0x1985e002 at offset 0x020f7e00

Messages which result in my mtd/jffs2 code marking the block bad. What I find strange is that a subsequent scan list the new block at a different 16k offset when the device erasesize is 16k, in this case 0x020f0000. Is that because my device is 128Mb and JFFS2 is using this 'virtual erase size' of 32k ?

I have observed this now on several different NAND devices and it seems to be more prominent while performing small writes.

I am currently trying to work out if the erase is not completing, or this is the wrong block or something else.

Quoted 7 lines · Simon Haynes

I have experienced a problem in which a JFF2 filesystem on NAND became full. This is a root file system and constant writes to a logfile filled the filesystem. On investigation it was found that the NAND device now had hundreds of bad blocks.

I started to investigate this and found that JFFS2 was announcing

Quoted 7 lines

Newly-erased block contained word 0x1985e002 at offset 0x020f7e00

Messages which result in my mtd/jffs2 code marking the block bad. What I find strange is that a subsequent scan list the new block at a different 16k offset when the device erasesize is 16k, in this case 0x020f0000. Is that because my device is 128Mb and JFFS2 is using this 'virtual erase size' of 32k ?

Yes. The bad block code scans/marks physical blocks and JFFS2 operates on virtual ones, if the device size is big enough.

Quoted 5 lines

I have observed this now on several different NAND devices and it seems to be more prominent while performing small writes.

I am currently trying to work out if the erase is not completing, or this is the wrong block or something else.

Hmm, are you using Ready/Busy Pin or the timeout ?

tglx

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Thomas,

I am using the ready pin.

Quoted 3 lines · Simon Haynes

Thomas,

I am using the ready pin.

Hmm, the strange thing is, that it does not complain about a failed erase. It complaines, when checking if the chip is really erased.

Can you try the hack below, which invalidates the page cachen unconditionally on erase ?

tglx

RCS file: /home/cvs/mtd/drivers/mtd/nand/nand_base.c,v retrieving revision 1.121
diff -u -r1.121 nand_base.c

nand_base.c 19 Oct 2004 15:09:35 -0000 renamed from nand_base.c 6 Oct 2004 19:53:11 -0000 1.121 +0 -0

@@ -2091,8 +2091,7 @@
 
                /* Invalidate the page cache, if we erase the block

which contains
the current cached page */
- if (page <= this->pagebuf && this->pagebuf < (page +
pages_per_block))

nand_base.c 19 Oct 2004 15:09:35 -0000 renamed from nand_base.c 6 Oct 2004 19:53:11 -0000 1.121 +1 -1

-                       this->pagebuf = -1;
+               this->pagebuf = -1;
 
                this->erase_cmd (mtd, page & this->pagemask);

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Quoted 8 lines · Simon Haynes

I have experienced a problem in which a JFF2 filesystem on NAND became full.
This is a root file system and constant writes to a logfile filled the filesystem. On investigation it was found that the NAND device now had hundreds of bad blocks.

I started to investigate this and found that JFFS2 was announcing

Quoted 8 lines

Newly-erased block contained word 0x1985e002 at offset 0x020f7e00

Messages which result in my mtd/jffs2 code marking the block bad. What I find strange is that a subsequent scan list the new block at a different 16k offset when the device erasesize is 16k, in this case 0x020f0000.
Is that because my device is 128Mb and JFFS2 is using this 'virtual erase size' of 32k ?

Yes. The bad block code scans/marks physical blocks and JFFS2 operates
on virtual ones, if the device size is big enough.

Quoted 3 lines

I have observed this now on several different NAND devices and it seems to be more prominent while performing small writes.

Quoted 2 lines

I am currently trying to work out if the erase is not completing, or this is the wrong block or something else.

Hmm, are you using Ready/Busy Pin or the timeout ?

tglx

1. Do you know what usually causes the "Newly-erased block contained
word "... error?
Is it caused by a interrupted (or otherwise failed) erase? Would power-fail cause this?

2. Would this cause good blocks to be incorrectly [and permanently] marked as bad?

I think I may have seen something similar on my system. I'm considering writing a test to see if this is a problem for me, but I'd like to learn more about this also.

Quoted 4 lines · Michael Moedt

1. Do you know what usually causes the "Newly-erased block contained
word "... error?
Is it caused by a interrupted (or otherwise failed) erase? Would power-fail cause this?

It's caused by a failed erase. If the chip interface is correct then it is usually a problem of a bad page/block. If not (e.g. wrong timing) it might return too early from an erase.

Quoted 2 lines

2. Would this cause good blocks to be incorrectly [and permanently] marked as bad?

Only if failes 5 times after mount. The counter is reset with each mount.

Quoted 3 lines

I think I may have seen something similar on my system. I'm considering writing a test to see if this is a problem for me, but I'd like to learn more about this also.

Which version of the mtd/nand code ?

There was a problem with the page cache, which was not invalidated on erase some time ago, but its fixed.

tglx

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This 5 error business is only if you have relatively new code. Old code generates an incorrect and permanent bad block after 1 failure. I am testing the suggestion by Thomas that this is a page cache problem by always marking an erase page as invalid. No errors as yet but I will keep you posted.