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NFS: Prevent a deadlock in the new writeback code

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We have to unlock the nfs_page before we call nfs_end_page_writeback
to avoid races with functions that expect the page to be unlocked
when PG_locked and PG_writeback are not set.
The problem is that nfs_unlock_request also releases the nfs_page,
causing a deadlock if the release of the nfs_open_context
triggers an iput() while the PG_writeback flag is still set...

The solution is to separate the unlocking and release of the nfs_page,
so that we can do the former before nfs_end_page_writeback and the
latter after.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>
This commit is contained in:
Trond Myklebust
2012-05-09 14:30:35 -04:00
parent dc327ed4cd
commit 3aff4ebb95
3 changed files with 15 additions and 4 deletions
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6
fs/nfs/write.c
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@@ -628,8 +628,9 @@ static void nfs_write_completion(struct nfs_pgio_header *hdr)
remove_req:
nfs_inode_remove_request(req);
next:
nfs_unlock_request(req);
nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
nfs_release_request(req);
}
out:
hdr->release(hdr);
@@ -1042,8 +1043,9 @@ static void nfs_redirty_request(struct nfs_page *req)
struct page *page = req->wb_page;
nfs_mark_request_dirty(req);
nfs_unlock_request(req);
nfs_unlock_request_dont_release(req);
nfs_end_page_writeback(page);
nfs_release_request(req);
}
static void nfs_async_write_error(struct list_head *head)