New subject: [Bug 1025059] btrfs: Avoid truncate tailing page if fallocate range doesn't exceed

13 Feb 2017

      http://bugzilla.suse.com/show_bug.cgi?id=1025059

            Bug ID: 1025059
           Summary: btrfs: Avoid truncate tailing page if fallocate range
                    doesn't exceed
    Classification: openSUSE
           Product: openSUSE Distribution
           Version: Leap 42.1
          Hardware: Other
                OS: Other
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Kernel
          Assignee: jeffm@suse.com
          Reporter: jeffm@suse.com
        QA Contact: qa-bugs@suse.de
          Found By: ---
           Blocker: ---

From: Qu Wenruo 
Date: Wed, 14 Oct 2015 15:26:13 +0800
Subject: btrfs: Avoid truncate tailing page if fallocate range doesn't exceed
 inode size
Git-commit: 0f6925fa2907df58496cabc33fa4677c635e2223
Patch-mainline: v4.3-rc7
References: revisit

Current code will always truncate tailing page if its alloc_start is
smaller than inode size.

For example, the file extent layout is like:
0    4K    8K    16K    32K
|<-----Extent A---------------->|
|<--Inode size: 18K---------->|

But if calling fallocate even for range [0,4K), it will cause btrfs to
re-truncate the range [16,32K), causing COW and a new extent.

0    4K    8K    16K    32K
|///////|    <- Fallocate call range
|<-----Extent A-------->|<--B-->|

The cause is quite easy, just a careless btrfs_truncate_inode() in a
else branch without extra judgment.
Fix it by add judgment on whether the fallocate range is beyond isize.

Signed-off-by: Qu Wenruo 
Signed-off-by: Chris Mason 
Acked-by: Jeff Mahoney 
---
 fs/btrfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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[Bug 1025059] New: btrfs: Avoid truncate tailing page if fallocate range doesn't exceed

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