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Commit 3aff4ebb authored by Trond Myklebust's avatar Trond Myklebust
Browse files

NFS: Prevent a deadlock in the new writeback code 



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: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>
parent dc327ed4

fs/nfs/pagelist.c

+10 −2
Original line number Diff line number Diff line
@@ -128,10 +128,10 @@ nfs_create_request(struct nfs_open_context *ctx, struct inode *inode, 
}



/**

 * nfs_unlock_request - Unlock request and wake up sleepers.

 * nfs_unlock_request_dont_release - Unlock request and wake up sleepers.

 * @req:

 */

void nfs_unlock_request(struct nfs_page *req)

void nfs_unlock_request_dont_release(struct nfs_page *req)

{

	if (!NFS_WBACK_BUSY(req)) {

		printk(KERN_ERR "NFS: Invalid unlock attempted\n");
@@ -141,6 +141,14 @@ void nfs_unlock_request(struct nfs_page *req) 
	clear_bit(PG_BUSY, &req->wb_flags);

	smp_mb__after_clear_bit();

	wake_up_bit(&req->wb_flags, PG_BUSY);

}



/**

 * nfs_unlock_request - Unlock request and release the nfs_page

 */

void nfs_unlock_request(struct nfs_page *req)

{

	nfs_unlock_request_dont_release(req);

	nfs_release_request(req);

}

fs/nfs/write.c

+4 −2
Original line number Diff line number Diff line
@@ -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)

include/linux/nfs_page.h

+1 −0
Original line number Diff line number Diff line
@@ -96,6 +96,7 @@ extern bool nfs_generic_pg_test(struct nfs_pageio_descriptor *desc, 
				struct nfs_page *req);

extern  int nfs_wait_on_request(struct nfs_page *);

extern	void nfs_unlock_request(struct nfs_page *req);

extern void nfs_unlock_request_dont_release(struct nfs_page *req);



/*

 * Lock the page of an asynchronous request without getting a new reference