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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>
This commit is contained in:
Trond Myklebust 2017-09-09 12:28:01 -04:00
parent 196639ebbe
commit 137da553db
2 changed files with 22 additions and 9 deletions
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16
fs/nfs/pnfs_nfs.c
View File

@ -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);

15
fs/nfs/write.c
View File

@ -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);