Re: [PATCH] Btrfs: fix enospc error caused by wrong checks of the chunk allocation

On Tue, Jan 17, 2012 at 3:24 AM, Miao Xie [off-list ref] wrote:

When we did sysbench test for inline files, enospc error happened eas=

ily though

there was lots of free disk space which could be allocated for new ch=

unks.

Reproduce steps:
=A0# mkfs.btrfs -b $((2 * 1024 * 1024 * 1024)) <test partition>
=A0# mount <test partition> /mnt
=A0# ulimit -n 102400
=A0# cd /mnt
=A0# sysbench --num-threads=3D1 --test=3Dfileio --file-num=3D81920 \
=A0> --file-total-size=3D80M --file-block-size=3D1K --file-io-mode=3D=

sync \

=A0> --file-test-mode=3Dseqwr prepare
=A0# sysbench --num-threads=3D1 --test=3Dfileio --file-num=3D81920 \
=A0> --file-total-size=3D80M --file-block-size=3D1K --file-io-mode=3D=

sync \

=A0> --file-test-mode=3Dseqwr run
=A0<soon later, BUG_ON() was triggered by enospc error>

The reason of this bug is:
Now, we can reserve space which is larger than the free space in the =

chunks if

we have enough free disk space which can be used for new chunks. By t=

his way,

the space allocator should allocate a new chunk by force if there is =

no free

space in the free space cache. But there are two wrong checks which b=

reak this

operation.

One is
=A0 =A0 =A0 =A0if (ret =3D=3D -ENOSPC && num_bytes > min_alloc_size)
in btrfs_reserve_extent(), it is wrong, we should try to allocate a n=

ew chunk

even we fail to allocate free space by minimum allocable size.

The other is
=A0 =A0 =A0 =A0if (space_info->force_alloc)
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0force =3D space_info->force_alloc;
in do_chunk_alloc(). It makes the allocator ignore CHUNK_ALLOC_FORCE =

If someone

sets ->force_alloc to CHUNK_ALLOC_LIMITED, and makes the enospc error=

 happen.

Fix these two wrong checks. Especially the second one, we fix it by c=

hanging

the value of CHUNK_ALLOC_LIMITED and CHUNK_ALLOC_FORCE, and make
CHUNK_ALLOC_FORCE greater than CHUNK_ALLOC_LIMITED since CHUNK_ALLOC_=

=46ORCE has

higher priority. And if the value which is passed in by the caller is=

 greater

than ->force_alloc, use the passed value.

Signed-off-by: Miao Xie <redacted>
---
This patch is based on the new viro branch.

After applying this patch to the re-based integration branch, I was
able to clear an EFBIG error (that seemed to be related to chunk
allocation) I had previously been receiving while trying to balance a
partially corrupted partition.

I was receiving this bug from the btrfs_add_system_chunk() function
which had do_chunk_alloc() close up in the callback list.

Thanks.
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