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Message-ID: <51BC080D.1090405@huawei.com>
Date: Sat, 15 Jun 2013 14:22:05 +0800
From: shencanquan <shencanquan@...wei.com>
To: Jeff Liu <jeff.liu@...cle.com>
CC: Richard Yao <ryao@...too.org>, Mark Fasheh <mfasheh@...e.com>,
<linux-kernel@...r.kernel.org>, <kernel@...too.org>,
<linux-fsdevel@...r.kernel.org>,
Ocfs2-Devel <ocfs2-devel@....oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH 1/2] ocfs2: Fix llseek() semantics and do
some cleanup
Hello, Richard and Jeff,
we found that llseek has another bug when in SEEK_END. it should be
add the inode lock and unlock.
this bug can be reproduce the following scenario:
on one nodeA, open the file and then write some data to file and
close the file .
on another nodeB , open the file and llseek the end of file . the
position of file is old.
On 2013/6/15 13:09, Jeff Liu wrote:
> [Add ocfs2-devel to CC-list]
>
> Hello Richard,
>
> Thanks for your patch.
>
> On 06/15/2013 03:23 AM, Richard Yao wrote:
>
>> There are multiple issues with the custom llseek implemented in ocfs2 for
>> implementing SEEK_HOLE/SEEK_DATA.
>>
>> 1. It takes the inode->i_mutex lock before calling generic_file_llseek(), which
>> is unnecessary.
> Agree, but please see my comments below.
>
>> 2. It fails to take the filp->f_lock spinlock before modifying filp->f_pos and
>> filp->f_version, which differs from generic_file_llseek().
>>
>> 3. It does a offset> inode->i_sb->s_maxbytes check that permits seeking up to
>> the maximum file size possible on the ocfs2 filesystem, even when it is past
>> the end of the file. Seeking beyond that (if possible), would return EINVAL
>> instead of ENXIO.
>>
>> 4. The switch statement tries to cover all whence values when in reality it
>> should only care about SEEK_HOLE/SEEK_DATA. Any other cases should be passsed
>> to generic_file_llseek().
> I have another patch set for refactoring ocfs2_file_llseek() but not yet found time
> to run a comprehensive tests. It can solve the existing issues but also improved the
> SEEK_DATA/SEEK_HOLE for unwritten extents, i.e. OCFS2_EXT_UNWRITTEN.
>
> With this change, SEEK_DATA/SEEK_HOLE will go into separate function with a little code
> duplication instead of the current mix-ups in ocfs2_seek_data_hole_offset(), i.e,
>
> loff_t ocfs2_file_llseek()
> {
> switch (origin) {
> case SEEK_END:
> case SEEK_CUR:
> case SEEK_SET:
> return generic_file_llseek(file, offset, origin);
> case SEEK_DATA:
> return ocfs2_seek_data(file, offset);
> case SEEK_HOLE:
> return ocfs2_seek_hole(file, offset);
> default:
> return -EINVAL;
> }
> }
>
> I personally like keeping SEEK_DATA/SEEK_HOLE in switch...case style rather
> than dealing with them in a condition check block.
>
> Thanks,
> -Jeff
>
>> btrfs_file_llseek() and ocfs2_file_llseek() are extremely similar and
>> consequently, contain many of the same flaws. Li Dongyang filed a pull
>> request with ZFSOnLinux for SEEK_HOLE/SEEK_DATA support that included a
>> custom llseek function that appears to have been modelled after the one
>> in ocfs2. The similarity was strong enough that it suffered from many of
>> the same flaws, which I caught during review. I addressed the issues
>> with his patch with one that I wrote. Since a small percentage of Gentoo
>> Linux users are affected by these flaws, I decided to adapt that code
>> that to btrfs (separate patch) and ocfs2.
>>
>> Note that commit 48802c8ae2a9d618ec734a61283d645ad527e06c by Jeff Liu at
>> Oracle mostly addressed #3 in btrfs. The only lingering issue was that
>> the offset> inode->i_sb->s_maxbytes check became dead code. The ocfs2
>> code was not fortunate enough to have had a similar correction until
>> now.
>>
>> Signed-off-by: Richard Yao<ryao@...too.org>
>> ---
>> fs/ocfs2/file.c | 65 ++++++++++++++++++++++-----------------------------------
>> 1 file changed, 25 insertions(+), 40 deletions(-)
>>
>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>> index ff54014..84f8c9c 100644
>> --- a/fs/ocfs2/file.c
>> +++ b/fs/ocfs2/file.c
>> @@ -2615,54 +2615,39 @@ bail:
>> }
>>
>> /* Refer generic_file_llseek_unlocked() */
>> -static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
>> +static loff_t ocfs2_file_llseek(struct file *filp, loff_t offset, int whence)
>> {
>> - struct inode *inode = file->f_mapping->host;
>> - int ret = 0;
>> + if (whence == SEEK_DATA || whence == SEEK_HOLE) {
>> + struct inode *inode = filp->f_mapping->host;
>> + int ret;
>>
>> - mutex_lock(&inode->i_mutex);
>> + if (offset< 0&& !(filp->f_mode& FMODE_UNSIGNED_OFFSET))
>> + return -EINVAL;
>>
>> - switch (whence) {
>> - case SEEK_SET:
>> - break;
>> - case SEEK_END:
>> - offset += inode->i_size;
>> - break;
>> - case SEEK_CUR:
>> - if (offset == 0) {
>> - offset = file->f_pos;
>> - goto out;
>> + if (offset>= i_size_read(inode)) {
>> + return -ENXIO;
>> }
>> - offset += file->f_pos;
>> - break;
>> - case SEEK_DATA:
>> - case SEEK_HOLE:
>> - ret = ocfs2_seek_data_hole_offset(file,&offset, whence);
>> - if (ret)
>> - goto out;
>> - break;
>> - default:
>> - ret = -EINVAL;
>> - goto out;
>> - }
>>
>> - if (offset< 0&& !(file->f_mode& FMODE_UNSIGNED_OFFSET))
>> - ret = -EINVAL;
>> - if (!ret&& offset> inode->i_sb->s_maxbytes)
>> - ret = -EINVAL;
>> - if (ret)
>> - goto out;
>> + mutex_lock(&inode->i_mutex);
>> + ret = ocfs2_seek_data_hole_offset(filp,&offset, whence);
>> + mutex_unlock(&inode->i_mutex);
>> +
>> + if (ret) {
>> + return ret;
>> + }
>>
>> - if (offset != file->f_pos) {
>> - file->f_pos = offset;
>> - file->f_version = 0;
>> + if (offset != filp->f_pos) {
>> + spin_lock(&filp->f_lock);
>> + filp->f_pos = offset;
>> + filp->f_version = 0;
>> + spin_unlock(&filp->f_lock);
>> + }
>> +
>> + return offset;
>> }
>>
>> -out:
>> - mutex_unlock(&inode->i_mutex);
>> - if (ret)
>> - return ret;
>> - return offset;
>> + return generic_file_llseek(filp, offset, whence);
>> +
>> }
>>
>> const struct inode_operations ocfs2_file_iops = {
>
>
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel@....oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>
> .
>
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