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Commit 137da553 authored by Trond Myklebust's avatar Trond Myklebust
Browse files

NFS: nfs_lock_and_join_requests and nfs_scan_commit_list can deadlock 



Since the commit list is not ordered, it is possible for nfs_scan_commit_list
to hold a request that nfs_lock_and_join_requests() is waiting for, while
at the same time trying to grab a request that nfs_lock_and_join_requests
already holds.

Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent 196639eb

fs/nfs/pnfs_nfs.c

+11 −5
Original line number Diff line number Diff line
@@ -91,22 +91,28 @@ static int 
pnfs_generic_transfer_commit_list(struct list_head *src, struct list_head *dst,

				  struct nfs_commit_info *cinfo, int max)

{

	struct nfs_page *req;

	struct nfs_page *req, *tmp;

	int ret = 0;



	while(!list_empty(src)) {

		req = list_first_entry(src, struct nfs_page, wb_list);



restart:

	list_for_each_entry_safe(req, tmp, src, wb_list) {

		kref_get(&req->wb_kref);

		if (!nfs_lock_request(req)) {

			int status;



			/* Prevent deadlock with nfs_lock_and_join_requests */

			if (!list_empty(dst)) {

				nfs_release_request(req);

				continue;

			}

			/* Ensure we make progress to prevent livelock */

			mutex_unlock(&NFS_I(cinfo->inode)->commit_mutex);

			status = nfs_wait_on_request(req);

			nfs_release_request(req);

			mutex_lock(&NFS_I(cinfo->inode)->commit_mutex);

			if (status < 0)

				break;

			continue;

			goto restart;

		}

		nfs_request_remove_commit_list(req, cinfo);

		clear_bit(PG_COMMIT_TO_DS, &req->wb_flags);

fs/nfs/write.c

+11 −4
Original line number Diff line number Diff line
@@ -1028,21 +1028,28 @@ int 
nfs_scan_commit_list(struct list_head *src, struct list_head *dst,

		     struct nfs_commit_info *cinfo, int max)

{

	struct nfs_page *req;

	struct nfs_page *req, *tmp;

	int ret = 0;



	while(!list_empty(src)) {

		req = list_first_entry(src, struct nfs_page, wb_list);

restart:

	list_for_each_entry_safe(req, tmp, src, wb_list) {

		kref_get(&req->wb_kref);

		if (!nfs_lock_request(req)) {

			int status;



			/* Prevent deadlock with nfs_lock_and_join_requests */

			if (!list_empty(dst)) {

				nfs_release_request(req);

				continue;

			}

			/* Ensure we make progress to prevent livelock */

			mutex_unlock(&NFS_I(cinfo->inode)->commit_mutex);

			status = nfs_wait_on_request(req);

			nfs_release_request(req);

			mutex_lock(&NFS_I(cinfo->inode)->commit_mutex);

			if (status < 0)

				break;

			continue;

			goto restart;

		}

		nfs_request_remove_commit_list(req, cinfo);

		nfs_list_add_request(req, dst);