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cifs: Avoid calling unlock_page() twice in cifs_readpage() when using fscache 

When reading a single page with cifs_readpage(), we make a call to
fscache_read_or_alloc_page() which once done, asynchronously calls
the completion function cifs_readpage_from_fscache_complete(). This
completion function unlocks the page once it has been populated from
cache. The module then attempts to unlock the page a second time in
cifs_readpage() which leads to warning messages.

In case of a successful call to fscache_read_or_alloc_page() we should skip
the second unlock_page() since this will be called by the
cifs_readpage_from_fscache_complete() once the page has been populated by
fscache.

With the modifications to cifs_readpage_worker(), we will need to re-grab the
page lock in cifs_write_begin().

The problem was first noticed when testing new fscache patches for cifs.
https://bugzilla.redhat.com/show_bug.cgi?id=1005737

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
This commit is contained in:
Sachin Prabhu 2013-09-13 14:11:57 +01:00 committed by Steve French
parent a9e9b7bc15
commit 466bd31bbd
1 changed files with 7 additions and 3 deletions
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10
fs/cifs/file.c
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@ -3419,6 +3419,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page,
io_error:
kunmap(page);
unlock_page(page);
read_complete:
return rc;
@ -3443,8 +3444,6 @@ static int cifs_readpage(struct file *file, struct page *page)
rc = cifs_readpage_worker(file, page, &offset);
unlock_page(page);
free_xid(xid);
return rc;
}
@ -3498,6 +3497,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
{
int oncethru = 0;
pgoff_t index = pos >> PAGE_CACHE_SHIFT;
loff_t offset = pos & (PAGE_CACHE_SIZE - 1);
loff_t page_start = pos & PAGE_MASK;
@ -3507,6 +3507,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len);
start:
page = grab_cache_page_write_begin(mapping, index, flags);
if (!page) {
rc = -ENOMEM;
@ -3548,13 +3549,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
}
}
if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) {
/*
* might as well read a page, it is fast enough. If we get
* an error, we don't need to return it. cifs_write_end will
* do a sync write instead since PG_uptodate isn't set.
*/
cifs_readpage_worker(file, page, &page_start);
page_cache_release(page);
oncethru = 1;
goto start;
} else {
/* we could try using another file handle if there is one -
but how would we lock it to prevent close of that handle