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2011-02-25Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstableLinus Torvalds10-57/+282
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: Btrfs: fix fiemap bugs with delalloc Btrfs: set FMODE_EXCL in btrfs_device->mode Btrfs: make btrfs_rm_device() fail gracefully Btrfs: Avoid accessing unmapped kernel address Btrfs: Fix BTRFS_IOC_SUBVOL_SETFLAGS ioctl Btrfs: allow balance to explicitly allocate chunks as it relocates Btrfs: put ENOSPC debugging under a mount option
2011-02-23Btrfs: fix fiemap bugs with delallocChris Mason3-42/+224
The Btrfs fiemap code wasn't properly returning delalloc extents, so applications that trust fiemap to decide if there are holes in the file see holes instead of delalloc. This reworks the btrfs fiemap code, adding a get_extent helper that searches for delalloc ranges and also adding a helper for extent_fiemap that skips past holes in the file. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: set FMODE_EXCL in btrfs_device->modeIlya Dryomov1-1/+1
This fixes a bug introduced in d4d77629, where the device added online (and therefore initialized via btrfs_init_new_device()) would be left with the positive bdev->bd_holders after unmount. Since d4d77629 we no longer OR FMODE_EXCL explicitly on blkdev_put(), set it in btrfs_device->mode. Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: make btrfs_rm_device() fail gracefullyIlya Dryomov1-2/+9
If shrinking done as part of the online device removal fails add that device back to the allocation list and increment the rw_devices counter. This fixes two bugs: 1) we could have a perfectly good device out of alloc list for no good reason; 2) in the btrfs consisting of two devices, failure in btrfs_rm_device() could lead to a situation where it was impossible to remove any of the devices because of the "unable to remove the only writeable device" error. Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: Avoid accessing unmapped kernel addressLi Zefan1-7/+14
When decompressing a chunk of data, we'll copy the data out to a working buffer if the data is stored in more than one page, otherwise we'll use the mapped page directly to avoid memory copy. In the latter case, we'll end up accessing the kernel address after we've unmapped the page in a corner case. Reported-by: Juan Francisco Cantero Hurtado <iam@juanfra.info> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: Fix BTRFS_IOC_SUBVOL_SETFLAGS ioctlLi Zefan1-2/+5
- Check user-specified flags correctly - Check the inode owership - Search root item in root tree but not fs tree Reported-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: allow balance to explicitly allocate chunks as it relocatesChris Mason3-1/+21
Btrfs device shrinking and balancing ends up reallocating all the blocks in order to allow COW to move them to new destinations. It is somewhat awkward in terms of ENOSPC because most of the enospc code is built around the idea that some operation on a reference counted tree triggers allocations in the non-reference counted trees. This commit changes the balancing code to deal with enospc by trying to allocate a new chunk. If that allocation succeeds, we go ahead and retry whatever failed due to enospc. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-16Btrfs: put ENOSPC debugging under a mount optionChris Mason3-2/+8
ENOSPC in btrfs is getting to the point where the extra debugging isn't required. I've put it under mount -o enospc_debug just in case someone is having difficult problems. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-15Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstableLinus Torvalds9-11/+68
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: Btrfs: check return value of alloc_extent_map() Btrfs - Fix memory leak in btrfs_init_new_device() btrfs: prevent heap corruption in btrfs_ioctl_space_info() Btrfs: Fix balance panic Btrfs: don't release pages when we can't clear the uptodate bits Btrfs: fix page->private races
2011-02-14Btrfs: check return value of alloc_extent_map()Tsutomu Itoh4-3/+7
I add the check on the return value of alloc_extent_map() to several places. In addition, alloc_extent_map() returns only the address or NULL. Therefore, check by IS_ERR() is unnecessary. So, I remove IS_ERR() checking. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-14Btrfs - Fix memory leak in btrfs_init_new_device()Ilya Dryomov1-0/+2
Memory allocated by calling kstrdup() should be freed. Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-14btrfs: prevent heap corruption in btrfs_ioctl_space_info()Dan Rosenberg1-2/+8
Commit bf5fc093c5b625e4259203f1cee7ca73488a5620 refactored btrfs_ioctl_space_info() and introduced several security issues. space_args.space_slots is an unsigned 64-bit type controlled by a possibly unprivileged caller. The comparison as a signed int type allows providing values that are treated as negative and cause the subsequent allocation size calculation to wrap, or be truncated to 0. By providing a size that's truncated to 0, kmalloc() will return ZERO_SIZE_PTR. It's also possible to provide a value smaller than the slot count. The subsequent loop ignores the allocation size when copying data in, resulting in a heap overflow or write to ZERO_SIZE_PTR. The fix changes the slot count type and comparison typecast to u64, which prevents truncation or signedness errors, and also ensures that we don't copy more data than we've allocated in the subsequent loop. Note that zero-size allocations are no longer possible since there is already an explicit check for space_args.space_slots being 0 and truncation of this value is no longer an issue. Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: Josef Bacik <josef@redhat.com> Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-14Btrfs: Fix balance panicYan, Zheng1-0/+1
Mark the cloned backref_node as checked in clone_backref_node() Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-14Btrfs: don't release pages when we can't clear the uptodate bitsChris Mason1-1/+9
Btrfs tracks uptodate state in an rbtree as well as in the page bits. This is supposed to enable us to use block sizes other than the page size, but there are a few parts still missing before that completely works. But, our readpage routine trusts this additional range based tracking of uptodateness, much in the same way the buffer head up to date bits are trusted for the other filesystems. The problem is that sometimes we need to allocate memory in order to split records in the rbtree, even when we are just clearing bits. This can be difficult when our clearing function is called GFP_ATOMIC, which can happen in the releasepage path. So, what happens today looks like this: releasepage called with GFP_ATOMIC btrfs_releasepage calls clear_extent_bit clear_extent_bit fails to allocate ram, leaving the up to date bit set btrfs_releasepage returns success The end result is the page being gone, but btrfs thinking the range is up to date. Later on if someone tries to read that same page, the btrfs readpage code will return immediately thinking the page is already up to date. This commit fixes things to fail the releasepage when we can't clear the extent state bits. It covers both data pages and metadata tree blocks. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-14Btrfs: fix page->private racesChris Mason2-5/+41
There is a race where btrfs_releasepage can drop the page->private contents just as alloc_extent_buffer is setting up pages for metadata. Because of how the Btrfs page flags work, this results in us skipping the crc on the page during IO. This patch sovles the race by waiting until after the extent buffer is inserted into the radix tree before it sets page private. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-07Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstableLinus Torvalds18-116/+371
* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: (33 commits) Btrfs: Fix page count calculation btrfs: Drop __exit attribute on btrfs_exit_compress btrfs: cleanup error handling in btrfs_unlink_inode() Btrfs: exclude super blocks when we read in block groups Btrfs: make sure search_bitmap finds something in remove_from_bitmap btrfs: fix return value check of btrfs_start_transaction() btrfs: checking NULL or not in some functions Btrfs: avoid uninit variable warnings in ordered-data.c Btrfs: catch errors from btrfs_sync_log Btrfs: make shrink_delalloc a little friendlier Btrfs: handle no memory properly in prepare_pages Btrfs: do error checking in btrfs_del_csums Btrfs: use the global block reserve if we cannot reserve space Btrfs: do not release more reserved bytes to the global_block_rsv than we need Btrfs: fix check_path_shared so it returns the right value btrfs: check return value of btrfs_start_ioctl_transaction() properly btrfs: fix return value check of btrfs_join_transaction() fs/btrfs/inode.c: Add missing IS_ERR test btrfs: fix missing break in switch phrase btrfs: fix several uncheck memory allocations ...
2011-02-07Btrfs: Fix page count calculationYan, Zheng1-4/+4
take offset of start position into account when calculating page count. Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-06btrfs: Drop __exit attribute on btrfs_exit_compressAlexey Charkov1-1/+1
As this function is called in some error paths while not removing the module, the __exit attribute prevents the kernel image from linking when btrfs is compiled in statically. Signed-off-by: Alexey Charkov <alchark@gmail.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-06btrfs: cleanup error handling in btrfs_unlink_inode()Tsutomu Itoh1-1/+1
When btrfs_alloc_path() fails, btrfs_free_path() need not be called. Therefore, it changes the branch ahead. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-06Btrfs: exclude super blocks when we read in block groupsJosef Bacik1-8/+18
This has been resulting in a BUT_ON(ret) after btrfs_reserve_extent in btrfs_cow_file_range. The reason is we don't actually calculate the bytes_super for a block group until we go to cache it, which means that the space_info can hand out reservations for space that it doesn't actually have, and we can run out of data space. This is also a problem if you are using space caching since we don't ever calculate bytes_super for the block groups. So instead everytime we read a block group call exclude_super_stripes, which calculates the bytes_super for the block group so it can be left out of the space_info. Then whenever caching completes we just call free_excluded_extents so that the super excluded extents are freed up. Also if we are unmounting and we hit any block groups that haven't been cached we still need to call free_excluded_extents to make sure things are cleaned up properly. Thanks, Reported-by: Arne Jansen <sensille@gmx.net> Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-06Btrfs: make sure search_bitmap finds something in remove_from_bitmapJosef Bacik1-0/+1
When we're cleaning up the tree log we need to be able to remove free space from the block group. The problem is if that free space spans bitmaps we would not find the space since we're looking for too many bytes. So make sure the amount of bytes we search for is limited to either the number of bytes we want, or the number of bytes left in the bitmap. This was tested by a user who was hitting the BUG() after search_bitmap. With this patch he can now mount his fs. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-01btrfs: fix return value check of btrfs_start_transaction()Tsutomu Itoh7-6/+37
The error check of btrfs_start_transaction() is added, and the mistake of the error check on several places is corrected. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-02-01btrfs: checking NULL or not in some functionsTsutomu Itoh3-0/+10
Because NULL is returned when the memory allocation fails, it is checked whether it is NULL. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-31Btrfs: avoid uninit variable warnings in ordered-data.cChris Mason1-1/+1
This one isn't really an uninit variable, but for pretty obscure reasons. Let's make it clearly correct. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-31Btrfs: catch errors from btrfs_sync_logChris Mason1-1/+2
btrfs_sync_log returns -EAGAIN when we need full transaction commits instead of small log commits, but sometimes we were dropping the return value. In practice, we check for this a few different ways, but this is still a bug that can leave off full log commits when we really need them. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-31Btrfs: make shrink_delalloc a little friendlierJosef Bacik1-3/+14
Xfstests 224 will just sit there and spin for ever until eventually we give up flushing delalloc and exit. On my box this took several hours. I could not interrupt this process either, even though we use INTERRUPTIBLE. So do 2 things 1) Keep us from looping over and over again without reclaiming anything 2) If we get interrupted exit the loop I tested this and the test now exits in a reasonable amount of time, and can be interrupted with ctrl+c. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Btrfs: handle no memory properly in prepare_pagesJosef Bacik1-2/+6
Instead of doing a BUG_ON(1) in prepare_pages if grab_cache_page() fails, just loop through the pages we've already grabbed and unlock and release them, then return -ENOMEM like we should. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Btrfs: do error checking in btrfs_del_csumsJosef Bacik1-0/+3
Got a report of a box panicing because we got a NULL eb in read_extent_buffer. His fs was borked and btrfs_search_path returned EIO, but we don't check for errors so the box paniced. Yes I know this will just make something higher up the stack panic, but that's a problem for future Josef. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Btrfs: use the global block reserve if we cannot reserve spaceJosef Bacik1-1/+27
We call use_block_rsv right before we make an allocation in order to make sure we have enough space. Now normally people have called btrfs_start_transaction() with the appropriate amount of space that we need, so we just use some of that pre-reserved space and move along happily. The problem is where people use btrfs_join_transaction(), which doesn't actually reserve any space. So we try and reserve space here, but we cannot flush delalloc, so this forces us to return -ENOSPC when in reality we have plenty of space. The most common symptom is seeing a bunch of "couldn't dirty inode" messages in syslog. With xfstests 224 we end up falling back to start_transaction and then doing all the flush delalloc stuff which causes to hang for a very long time. So instead steal from the global reserve, which is what this is meant for anyway. With this patch and the other 2 I have sent xfstests 224 now passes successfully. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Btrfs: do not release more reserved bytes to the global_block_rsv than we needJosef Bacik1-2/+14
When we do btrfs_block_rsv_release, if global_block_rsv is not full we will release all the extra bytes to global_block_rsv, even if it's only a little short of the amount of space that we need to reserve. This causes us to starve ourselves of reservable space during the transaction which will force us to shrink delalloc bytes and commit the transaction more often than we should. So instead just add the amount of bytes we need to add to the global reserve so reserved == size, and then add the rest back into the space_info for general use. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Btrfs: fix check_path_shared so it returns the right valueJosef Bacik1-2/+3
When running xfstests 224 I kept getting ENOSPC when trying to remove the files, and this is because we were returning ret from check_path_shared while it was uninitalized, which isn't right. Fix this to return 0 properly, and now xfstests 224 doesn't freak out when it tries to clean itself up. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28btrfs: check return value of btrfs_start_ioctl_transaction() properlyTsutomu Itoh1-1/+1
btrfs_start_ioctl_transaction() returns ERR_PTR(), not NULL. So, it is necessary to use IS_ERR() to check the return value. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28btrfs: fix return value check of btrfs_join_transaction()Tsutomu Itoh6-13/+51
The error check of btrfs_join_transaction()/btrfs_join_transaction_nolock() is added, and the mistake of the error check in several places is corrected. For more stable Btrfs, I think that we should reduce BUG_ON(). But, I think that long time is necessary for this. So, I propose this patch as a short-term solution. With this patch: - To more stable Btrfs, the part that should be corrected is clarified. - The panic isn't done by the NULL pointer reference etc. (even if BUG_ON() is increased temporarily) - The error code is returned in the place where the error can be easily returned. As a long-term plan: - BUG_ON() is reduced by using the forced-readonly framework, etc. Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28fs/btrfs/inode.c: Add missing IS_ERR testJulia Lawall1-1/+1
After the conditional that precedes the following code, inode may be an ERR_PTR value. This can eg result from a memory allocation failure via the call to btrfs_iget, and thus does not imply that root is different than sub_root. Thus, an IS_ERR check is added to ensure that there is no dereference of inode in this case. The semantic match that finds this problem is as follows: (http://coccinelle.lip6.fr/) // <smpl> @r@ identifier f; @@ f(...) { ... return ERR_PTR(...); } @@ identifier r.f, fld; expression x; statement S1,S2; @@ x = f(...) ... when != IS_ERR(x) ( if (IS_ERR(x) ||...) S1 else S2 | *x->fld ) // </smpl> Signed-off-by: Julia Lawall <julia@diku.dk> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28btrfs: fix missing break in switch phraseliubo1-0/+1
There is a missing break in switch, fix it. Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28btrfs: fix several uncheck memory allocationsliubo4-0/+33
To make btrfs more stable, add several missing necessary memory allocation checks, and when no memory, return proper errno. We've checked that some of those -ENOMEM errors will be returned to userspace, and some will be catched by BUG_ON() in the upper callers, and none will be ignored silently. Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28btrfs: fix uncheck memory allocation in btrfs_submit_compressed_readliubo2-4/+25
btrfs_submit_compressed_read() is lack of memory allocation checks and corresponding error route. After this fix, if it comes to "no memory" case, errno will be returned to userland step by step, and tell users this operation cannot go on. Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-01-28Merge branch 'bug-fixes' of git://repo.or.cz/linux-btrfs-devel into btrfs-38Chris Mason6-65/+117
2011-01-27Btrfs: Fix file clone when source offset is not 0Li Zefan1-1/+4
Suppose: - the source extent is: [0, 100] - the src offset is 10 - the clone length is 90 - the dest offset is 0 This statement: new_key.offset = key.offset + destoff - off will produce such an extent for the dest file: [ino, BTRFS_EXTENT_DATA_KEY, -10] , which is obviously wrong. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27Btrfs: Fix memory leak in writepage fixup workMiao Xie1-0/+1
fixup, which is allocated when starting page write to fix up the extent without ORDERED bit set, should be freed after this work is done. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27Btrfs: Don't return acl info when mounting with noacl optionMiao Xie1-0/+6
Steps to reproduce: # mkfs.btrfs /dev/sda2 # mount /dev/sda2 /mnt # touch /mnt/file0 # setfacl -m 'u:root:x,g::x,o::x' /mnt/file0 # umount /mnt # mount /dev/sda2 -o noacl /mnt # getfacl /mnt/file0 ... user::rw- user:root:--x group::--x mask::--x other::--x The output should be: user::rw- group::--x other::--x Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27Btrfs: Free correct pointer after using strsepTero Roponen1-2/+3
We must save and free the original kstrdup()'ed pointer because strsep() modifies its first argument. Signed-off-by: Tero Roponen <tero.roponen@gmail.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27Btrfs: Fix memory leak on finding existing superIan Kent1-0/+2
We missed a memory deallocation in commit 450ba0ea. If an existing super block is found at mount and there is no error condition then the pre-allocated tree_root and fs_info are no not used and are not freeded. Signed-off-by: Ian Kent <raven@themaw.net> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27Btrfs: Fix memory leak at umountLi Zefan1-0/+2
fs_info, which is allocated in open_ctree(), should be freed in close_ctree(). Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Check mergeable free space when removing a clusterLi Zefan1-6/+20
After returing extents from a cluster to the block group, some extents in the block group may be mergeable. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Add a helper try_merge_free_space()Li Zefan1-32/+43
When adding a new extent, we'll firstly see if we can merge this extent to the left or/and right extent. Extract this as a helper try_merge_free_space(). As a side effect, we fix a small bug that if the new extent has non-bitmap left entry but is unmergeble, we'll directly link the extent without trying to drop it into bitmap. This also prepares for the next patch. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Update stats when allocating from a clusterLi Zefan1-3/+14
When allocating extent entry from a cluster, we should update the free_space and free_extents fields of the block group. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Free fully occupied bitmap in clusterLi Zefan1-0/+2
If there's no more free space in a bitmap, we should free it. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Add helper function free_bitmap()Li Zefan1-21/+16
Remove some duplicated code. This prepares for the next patch. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
2011-01-27btrfs: Fix threshold calculation for block groups smaller than 1GBLi Zefan1-2/+6
If a block group is smaller than 1GB, the extent entry threadhold calculation will always set the threshold to 0. So as free space gets fragmented, btrfs will switch to use bitmap to manage free space, but then will never switch back to extents due to this bug. Reviewed-by: Josef Bacik <josef@redhat.com> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>