On 2011-05-13, at 12:34 AM, Lukas Czerner wrote:

On Wed, 11 May 2011, Kazuya Mio wrote:

quoted

We hit BUG_ON in ext4_ext_put_gap_in_cache() while creating a file
whose size is the max file size of extent format. Because the extent cache
length is 0 when we allocate two blocks to the file offset 2^32-2, and then
the offset 2^32-1. To fix it, we decrease the max file size to
(2^32-2)*blocksize. In this way, we would be able to allocate a block up to
the offset 2^32-2. I think there is no data loss because we can read all files
created before applying this patch.

How to reproduce:
I'm running 2.6.39-rc6. Note that i386 architecture and 4KB blocksize cannot
reproduce this problem.

# dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-2))
# sync
# dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-1))

Hi Kazuya,

Thanks for the patch, however I think that there is a better solution
than lowering the max file size, which is not necessary. I would rather
fix ext4_ext_put_gap_in_cache() and allow to invalidate the cache by
setting the length to zero.

Please see the following patch, if it works for you.

This thread has stalled.  Until we can come up with a better fix, I think
we should land Kazuya's patch for the current merge window and then worry
about allocating that last 4kB at the end of the 16TB file later (2.3e-6%
of the file :-).

quoted

Signed-off-by: Kazuya Mio <redacted>
---
fs/ext4/super.c |    2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 8553dfb..fce0249 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c

@@ -2248,8 +2248,8 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)

	/* 32-bit extent-start container, ee_block */
	res = 1LL << 32;
-	res <<= blkbits;
	res -= 1;
+	res <<= blkbits;

	/* Sanity check against vm- & vfs- imposed limits */
	if (res > upper_limit)

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Cheers, Andreas