On Thu 22-07-10 08:03:18, shenghui wrote: > 2010/7/22 Jan Kara <jack@xxxxxxx>: > >> Hi, > >> I walked through ext2_xattr_get, and felt that we can > >> do some optimization on it. For name_len check, it's done > >> after down xattr_sem and sb_read, both of which are time > >> consuming operation compared with strlen: > >> down_read(&EXT2_I(inode)->xattr_sem); > >> ... > >> bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl); > >> ... > >> /* find named attribute */ > >> name_len = strlen(name); > >> > >> error = -ERANGE; > >> if (name_len > 255) > >> goto cleanup; > >> > >> Most of the case, you'll get one valid block, but if the > >> name len > 255, then the xattr_sem down and sb_bread operation > >> can be seen as a waste of time. So I think we'd better do > >> name len check as early as possible. > >> Following is my patch, and it's against 2.6.35-rc4. > >> Please check it. > >> > >> Signed-off-by: Wang Sheng-Hui <crosslonelyover@xxxxxxxxx> > >> --- > >> fs/ext2/xattr.c | 12 +++++++----- > >> 1 files changed, 7 insertions(+), 5 deletions(-) > >> > >> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c > >> index 7c39157..0b94d61 100644 > >> --- a/fs/ext2/xattr.c > >> +++ b/fs/ext2/xattr.c > >> @@ -161,6 +161,13 @@ ext2_xattr_get(struct inode *inode, int name_index, const char *name, > >> > >> if (name == NULL) > >> return -EINVAL; > >> + > >> + /* find named attribute */ > >> + name_len = strlen(name); > >> + error = -ERANGE; > >> + if (name_len > 255) > >> + goto cleanup; > > But you cannot go to cleanup here because you don't hold xattr_sem... > > > > Sorry, I'm a little confused by your words. > The patch just checks name_len, and it > doesn't need xattr_sem. Checking of name_len is fine as you did it. But I wanted to point out that if name_len is greater than 255, you then go to 'cleanup' label which tries to do up_read(&EXT2_I(inode)->xattr_sem). But that's a bug because after you moved the code, we don't hold xattr_sem at the moment we check name_len. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
