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: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index ae26775..c3f627b 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -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);