Problems with JFFS2 FS during parallel write operations

[Geert Uytterhoeven]

On Mon, 1 Dec 2008, Ostendorf, Rainer wrote:
> i'm still working on the problem described in my previous post:
> 
> [...]
> > During normal operation the system runs perfectly stable, but when i 
> > start two processes running parallel, writing huge amounts of data 
> > to the flash device, i get error 
> > messages from the JFFS2 filesystem:
> > 
> > ...
> > argh. node added in wrong place
> > argh. node added in wrong place
> > ...
> > 
> > This message repeats for about 15-20 times while copying parallel 2 
> > files of about 6MByte to the flash via Ethernet (SCP). 
> [...]
> 
> As i can only reproduce the corruption of the JFFS2 FS during parallel access of at leat two processes writing to the flash, i assume that the cause for the corruption is some kind of race-condition. Have there been any known problems/bugs with race conditions, that could lead to an error like this? Would it probably help to upgrade to a newer kernel version? Any hint and help would be greatly appreciated.

Do you use LZO compression? If yes, it could have been this one:

commit dc8a0843a435b2c0891e7eaea64faaf1ebec9b11
Author: Geert Uytterhoeven <Geert.Uytterhoeven at sonycom.com>
Date:   Wed Nov 5 23:21:16 2008 +0100

    [JFFS2] fix race condition in jffs2_lzo_compress()
    
    deflate_mutex protects the globals lzo_mem and lzo_compress_buf.  However,
    jffs2_lzo_compress() unlocks deflate_mutex _before_ it has copied out the
    compressed data from lzo_compress_buf.  Correct this by moving the mutex
    unlock after the copy.
    
    In addition, document what deflate_mutex actually protects.
    
    Cc: stable at kernel.org
    Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven at sonycom.com>
    Acked-by: Richard Purdie <rpurdie at openedhand.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>

diff --git a/fs/jffs2/compr_lzo.c b/fs/jffs2/compr_lzo.c
index 47b0457..90cb60d 100644
--- a/fs/jffs2/compr_lzo.c
+++ b/fs/jffs2/compr_lzo.c
@@ -19,7 +19,7 @@
 
 static void *lzo_mem;
 static void *lzo_compress_buf;
-static DEFINE_MUTEX(deflate_mutex);
+static DEFINE_MUTEX(deflate_mutex);	/* for lzo_mem and lzo_compress_buf */
 
 static void free_workspace(void)
 {
@@ -49,18 +49,21 @@ static int jffs2_lzo_compress(unsigned char *data_in, unsigned char *cpage_out,
 
 	mutex_lock(&deflate_mutex);
 	ret = lzo1x_1_compress(data_in, *sourcelen, lzo_compress_buf, &compress_size, lzo_mem);
-	mutex_unlock(&deflate_mutex);
-
 	if (ret != LZO_E_OK)
-		return -1;
+		goto fail;
 
 	if (compress_size > *dstlen)
-		return -1;
+		goto fail;
 
 	memcpy(cpage_out, lzo_compress_buf, compress_size);
-	*dstlen = compress_size;
+	mutex_unlock(&deflate_mutex);
 
+	*dstlen = compress_size;
 	return 0;
+
+ fail:
+	mutex_unlock(&deflate_mutex);
+	return -1;
 }
 
 static int jffs2_lzo_decompress(unsigned char *data_in, unsigned char *cpage_out,


With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

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E-mail:   Geert.Uytterhoeven at sonycom.com
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