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ext4: add nowait mode for ext4_getblk()

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Current ext4_getblk() might sleep if some resources are not valid or
could be race with a concurrent extents modifing procedure. So we
cannot call ext4_getblk() and ext4_map_blocks() to get map blocks in
the atomic context in some fast path (e.g. the upcoming procedure of
getting symlink external block in the RCU context), even if the map
extents have already been check and cached.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/20220424140936.1898920-2-yi.zhang@huawei.com
This commit is contained in:
Zhang Yi 2022-04-24 22:09:35 +08:00 committed by Theodore Ts'o
parent e4e58e5df3
commit 9558cf14e8
2 changed files with 16 additions and 0 deletions
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2
fs/ext4/ext4.h
View file

@ -673,6 +673,8 @@ enum {
/* Caller will submit data before dropping transaction handle. This
* allows jbd2 to avoid submitting data before commit. */
#define EXT4_GET_BLOCKS_IO_SUBMIT 0x0400
/* Caller is in the atomic contex, find extent if it has been cached */
#define EXT4_GET_BLOCKS_CACHED_NOWAIT 0x0800
/*
* The bit position of these flags must not overlap with any of the

14
fs/ext4/inode.c
View file

@ -545,12 +545,21 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
} else {
BUG();
}
if (flags & EXT4_GET_BLOCKS_CACHED_NOWAIT)
return retval;
#ifdef ES_AGGRESSIVE_TEST
ext4_map_blocks_es_recheck(handle, inode, map,
&orig_map, flags);
#endif
goto found;
}
/*
* In the query cache no-wait mode, nothing we can do more if we
* cannot find extent in the cache.
*/
if (flags & EXT4_GET_BLOCKS_CACHED_NOWAIT)
return 0;
/*
* Try to see if we can get the block without requesting a new
@ -837,10 +846,12 @@ struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
struct ext4_map_blocks map;
struct buffer_head *bh;
int create = map_flags & EXT4_GET_BLOCKS_CREATE;
bool nowait = map_flags & EXT4_GET_BLOCKS_CACHED_NOWAIT;
int err;
ASSERT((EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY)
|| handle != NULL || create == 0);
ASSERT(create == 0 || !nowait);
map.m_lblk = block;
map.m_len = 1;
@ -851,6 +862,9 @@ struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
if (err < 0)
return ERR_PTR(err);
if (nowait)
return sb_find_get_block(inode->i_sb, map.m_pblk);
bh = sb_getblk(inode->i_sb, map.m_pblk);
if (unlikely(!bh))
return ERR_PTR(-ENOMEM);