2010/11/9 Jeff Layton <jlayton@xxxxxxxxxxxxxxx>:
> On Fri, 5 Nov 2010 11:29:34 +0300
> Pavel Shilovsky <piastryyy@xxxxxxxxx> wrote:
>
>> On strict cache mode if we don't have Exclusive oplock we write a data to
>> the server through cifs_user_write. Then if we Level II oplock store it in
>> the cache, otherwise - invalidate inode pages affected by this writing.
>>
>> Signed-off-by: Pavel Shilovsky <piastryyy@xxxxxxxxx>
>> ---
>> fs/cifs/cifsfs.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++-----
>> fs/cifs/file.c | 14 ++++++++++++--
>> 2 files changed, 58 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
>> index bb7f36e..fbcd219 100644
>> --- a/fs/cifs/cifsfs.c
>> +++ b/fs/cifs/cifsfs.c
>> @@ -596,12 +596,53 @@ static ssize_t cifs_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>> static ssize_t cifs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>> unsigned long nr_segs, loff_t pos)
>> {
>> - struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
>> - ssize_t written;
>> + struct inode *inode;
>> + struct cifs_sb_info *cifs_sb;
>> + ssize_t written, cache_written;
>> + loff_t saved_pos;
>> +
>> + inode = iocb->ki_filp->f_path.dentry->d_inode;
>> +
>> + if (CIFS_I(inode)->clientCanCacheAll)
>> + return generic_file_aio_write(iocb, iov, nr_segs, pos);
>> +
>> + cifs_sb = CIFS_SB(iocb->ki_filp->f_path.dentry->d_sb);
>> +
>> + if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_STRICT_IO) == 0) {
>> + int rc;
>> +
>> + written = generic_file_aio_write(iocb, iov, nr_segs, pos);
>> +
>> + rc = filemap_fdatawrite(inode->i_mapping);
>> + if (rc)
>> + cFYI(1, "cifs_file_aio_write: %d rc on %p inode",
>> + rc, inode);
>> + return written;
>> + }
>> +
>> + saved_pos = pos;
>> + written = cifs_user_write(iocb->ki_filp, iov->iov_base,
>> + iov->iov_len, &pos);
>> +
>> + if (written > 0 && CIFS_I(inode)->clientCanCacheRead) {
>> + /* we have data written to the server and at least oplock
>> + for reading - store the date in the cache */
>> + cache_written = generic_file_aio_write(iocb, iov,
>> + nr_segs, saved_pos);
>> + if (cache_written != written)
>> + cERROR(1, "Cache written and server written data "
>> + "lengths are different");
>> + return written;
>> + }
>> +
>> + if (written > 0)
>> + invalidate_mapping_pages(inode->i_mapping,
>> + saved_pos >> PAGE_CACHE_SHIFT,
>> + (saved_pos+iov->iov_len-1)
>> + >> PAGE_CACHE_SHIFT);
>> +
>> + iocb->ki_pos = pos;
>>
>> - written = generic_file_aio_write(iocb, iov, nr_segs, pos);
>> - if (!CIFS_I(inode)->clientCanCacheAll)
>> - filemap_fdatawrite(inode->i_mapping);
>> return written;
>> }
>>
>> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
>> index b36de2e..85824c0 100644
>> --- a/fs/cifs/file.c
>> +++ b/fs/cifs/file.c
>> @@ -1537,7 +1537,11 @@ static int cifs_write_end(struct file *file, struct address_space *mapping,
>> struct page *page, void *fsdata)
>> {
>> int rc;
>> - struct inode *inode = mapping->host;
>> + struct inode *inode;
>> + struct cifs_sb_info *cifs_sb;
>> +
>> + inode = mapping->host;
>> + cifs_sb = CIFS_SB(inode->i_sb);
>>
>> cFYI(1, "write_end for page %p from pos %lld with %d bytes",
>> page, pos, copied);
>> @@ -1570,7 +1574,13 @@ static int cifs_write_end(struct file *file, struct address_space *mapping,
>> } else {
>> rc = copied;
>> pos += copied;
>> - set_page_dirty(page);
>> + /* if we have strict cache switched on and don't have Exclusive
>> + oplock for the inode, we don't have to set_page_dirty
>> + because we flushed the data to the server in
>> + cifs_file_aio_write before */
>> + if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_STRICT_IO) == 0 ||
>> + CIFS_I(inode)->clientCanCacheAll)
>> + set_page_dirty(page);
>
> Is there a potential for a race here? Suppose I have clientCanCacheAll
> set, I write to the cache, but before I get to cifs_write_end, an
> oplock break is processed and clientCanCacheAll is cleared. Now I have
> dirty data in cache but the dirty flag doesn't get set. Does anything
> prevent that?
Yes, you are right. In the case of clientCanCacheAll and STRICT_IO set
- can we call set_page_dirty for every page affected by our write in
cifs_file_aio_write? It should prevent races, I think.
>
>> }
>>
>> if (rc > 0) {
>
--
Best regards,
Pavel Shilovsky.
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