knfsd: Replace lock_kernel with a mutex for nfsd thread startup/shutdown locking.

This removes the BKL from the RPC service creation codepath. The BKL
really isn't adequate for this job since some of this info needs
protection across sleeps.

Also, add some comments to try and clarify how the locking should work
and to make it clear that the BKL isn't necessary as long as there is
adequate locking between tasks when touching the svc_serv fields.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 23 insertions, 14 deletions

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 5ac00c4fee91..049d2a9c7715 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -450,22 +450,26 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size)
         int i;
         int rv;
         int len;
-        int npools = nfsd_nrpools();
+        int npools;
         int *nthreads;
 
+        mutex_lock(&nfsd_mutex);
+        npools = nfsd_nrpools();
         if (npools == 0) {
                 /*
                  * NFS is shut down.  The admin can start it by
                  * writing to the threads file but NOT the pool_threads
                  * file, sorry.  Report zero threads.
                  */
+                mutex_unlock(&nfsd_mutex);
                 strcpy(buf, "0\n");
                 return strlen(buf);
         }
 
         nthreads = kcalloc(npools, sizeof(int), GFP_KERNEL);
+        rv = -ENOMEM;
         if (nthreads == NULL)
-                return -ENOMEM;
+                goto out_free;
 
         if (size > 0) {
                 for (i = 0; i < npools; i++) {
@@ -496,10 +500,12 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size)
                 mesg += len;
         }
 
+        mutex_unlock(&nfsd_mutex);
         return (mesg-buf);
 
 out_free:
         kfree(nthreads);
+        mutex_unlock(&nfsd_mutex);
         return rv;
 }
 
@@ -566,14 +572,13 @@ static ssize_t write_versions(struct file *file, char *buf, size_t size)
         return len;
 }
 
-static ssize_t write_ports(struct file *file, char *buf, size_t size)
+static ssize_t __write_ports(struct file *file, char *buf, size_t size)
 {
         if (size == 0) {
                 int len = 0;
-                lock_kernel();
+
                 if (nfsd_serv)
                         len = svc_xprt_names(nfsd_serv, buf, 0);
-                unlock_kernel();
                 return len;
         }
         /* Either a single 'fd' number is written, in which
@@ -603,9 +608,7 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
                         /* Decrease the count, but don't shutdown the
                          * the service
                          */
-                        lock_kernel();
                         nfsd_serv->sv_nrthreads--;
-                        unlock_kernel();
                 }
                 return err < 0 ? err : 0;
         }
@@ -614,10 +617,8 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
                 int len = 0;
                 if (!toclose)
                         return -ENOMEM;
-                lock_kernel();
                 if (nfsd_serv)
                         len = svc_sock_names(buf, nfsd_serv, toclose);
-                unlock_kernel();
                 if (len >= 0)
                         lockd_down();
                 kfree(toclose);
@@ -655,7 +656,6 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
                 if (sscanf(&buf[1], "%15s %4d", transport, &port) == 2) {
                         if (port == 0)
                                 return -EINVAL;
-                        lock_kernel();
                         if (nfsd_serv) {
                                 xprt = svc_find_xprt(nfsd_serv, transport,
                                                      AF_UNSPEC, port);
@@ -666,13 +666,22 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
                                 } else
                                         err = -ENOTCONN;
                         }
-                        unlock_kernel();
                         return err < 0 ? err : 0;
                 }
         }
         return -EINVAL;
 }
 
+static ssize_t write_ports(struct file *file, char *buf, size_t size)
+{
+        ssize_t rv;
+        mutex_lock(&nfsd_mutex);
+        rv = __write_ports(file, buf, size);
+        mutex_unlock(&nfsd_mutex);
+        return rv;
+}
+
+
 int nfsd_max_blksize;
 
 static ssize_t write_maxblksize(struct file *file, char *buf, size_t size)
@@ -691,13 +700,13 @@ static ssize_t write_maxblksize(struct file *file, char *buf, size_t size)
                 if (bsize > NFSSVC_MAXBLKSIZE)
                         bsize = NFSSVC_MAXBLKSIZE;
                 bsize &= ~(1024-1);
-                lock_kernel();
+                mutex_lock(&nfsd_mutex);
                 if (nfsd_serv && nfsd_serv->sv_nrthreads) {
-                        unlock_kernel();
+                        mutex_unlock(&nfsd_mutex);
                         return -EBUSY;
                 }
                 nfsd_max_blksize = bsize;
-                unlock_kernel();
+                mutex_unlock(&nfsd_mutex);
         }
         return sprintf(buf, "%d\n", nfsd_max_blksize);
 }