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From: Jörn Engel on 17 Apr 2010 14:50
Moin David,

if I read the code correctly, JFFS2 will happily perform a NOP on
sys_sync() again. And this time it appears to be Jens' fault.

JFFS2 does not appear to set s_bdi anywhere. And as of 32a88aa1,
__sync_filesystem() will return 0 if s_bdi is not set. As a result,
sync_fs() is never called for jffs2 and whatever remains in the wbuf
will not make it to the device.

The patch also adds a BUG_ON to catch this problem in any remaining or
future offenders. I am not sure about network filesystems, but at
least bdev- and mtd-based ones should be caught.

Opinions?

Jörn

--
No art, however minor, demands less than total dedication if you want
to excel in it.
-- Leon Battista Alberti

diff --git a/drivers/mtd/mtdsuper.c b/drivers/mtd/mtdsuper.c
index af8b42e..7c00319 100644
--- a/drivers/mtd/mtdsuper.c
+++ b/drivers/mtd/mtdsuper.c
@@ -13,6 +13,7 @@
#include <linux/mtd/super.h>
#include <linux/namei.h>
#include <linux/ctype.h>
+#include <linux/slab.h>

/*
* compare superblocks to see if they're equivalent
@@ -44,6 +45,7 @@ static int get_sb_mtd_set(struct super_block *sb, void *_mtd)

sb->s_mtd = mtd;
sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, mtd->index);
+ sb->s_bdi = mtd->backing_dev_info;
return 0;
}

diff --git a/fs/super.c b/fs/super.c
index f35ac60..e8af253 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -954,10 +954,12 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
if (error < 0)
goto out_free_secdata;
BUG_ON(!mnt->mnt_sb);
+ BUG_ON(!mnt->mnt_sb->s_bdi &&
+ (mnt->mnt_sb->s_bdev || mnt->mnt_sb->s_mtd));

- error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
- if (error)
- goto out_sb;
+ error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
+ if (error)
+ goto out_sb;

/*
* filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
--
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Prev: drivers/uio/uio.c: DMA mapping, interrupt extensions, etc.
Next: change msr numbers for kvmclock