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ext4: Clear the unwritten buffer_head flag after the extent is initialized

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The BH_Unwritten flag indicates that the buffer is allocated on disk
but has not been written; that is, the disk was part of a persistent
preallocation area.  That flag should only be set when a get_blocks()
function is looking up a inode's logical to physical block mapping.

When ext4_get_blocks_wrap() is called with create=1, the uninitialized
extent is converted into an initialized one, so the BH_Unwritten flag
is no longer appropriate.  Hence, we need to make sure the
BH_Unwritten is not left set, since the combination of BH_Mapped and
BH_Unwritten is not allowed; among other things, it will result ext4's
get_block() to be called over and over again during the write_begin
phase of write(2).

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Aneesh Kumar K.V 2009-05-14 17:05:39 -04:00 committed by Theodore Ts'o
parent 33b9817e2a
commit 2a8964d63d
1 changed files with 13 additions and 0 deletions
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13
fs/ext4/inode.c
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@ -1149,6 +1149,7 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
int retval; int retval;
clear_buffer_mapped(bh); clear_buffer_mapped(bh);
clear_buffer_unwritten(bh);
/* /*
* Try to see if we can get the block without requesting * Try to see if we can get the block without requesting
@ -1178,6 +1179,18 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
if (retval > 0 && buffer_mapped(bh)) if (retval > 0 && buffer_mapped(bh))
return retval; return retval;
/*
* When we call get_blocks without the create flag, the
* BH_Unwritten flag could have gotten set if the blocks
* requested were part of a uninitialized extent. We need to
* clear this flag now that we are committed to convert all or
* part of the uninitialized extent to be an initialized
* extent. This is because we need to avoid the combination
* of BH_Unwritten and BH_Mapped flags being simultaneously
* set on the buffer_head.
*/
clear_buffer_unwritten(bh);
/* /*
* New blocks allocate and/or writing to uninitialized extent * New blocks allocate and/or writing to uninitialized extent
* will possibly result in updating i_data, so we take * will possibly result in updating i_data, so we take