fs/locks.c: prepare for BKL removal

This prepares the removal of the big kernel lock from the
file locking code. We still use the BKL as long as fs/lockd
uses it and ceph might sleep, but we can flip the definition
to a private spinlock as soon as that's done.
All users outside of fs/lockd get converted to use
lock_flocks() instead of lock_kernel() where appropriate.

Based on an earlier patch to use a spinlock from Matthew
Wilcox, who has attempted this a few times before, the
earliest patch from over 10 years ago turned it into
a semaphore, which ended up being slower than the BKL
and was subsequently reverted.

Someone should do some serious performance testing when
this becomes a spinlock, since this has caused problems
before. Using a spinlock should be at least as good
as the BKL in theory, but who knows...

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Sage Weil <sage@newdream.net>
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org

1 files changed, 68 insertions, 44 deletions

diff --git a/fs/locks.c b/fs/locks.c
index ab24d49fc048..8b2b6ad56a09 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -143,6 +143,22 @@ int lease_break_time = 45;
 static LIST_HEAD(file_lock_list);
 static LIST_HEAD(blocked_list);
 
+/*
+ * Protects the two list heads above, plus the inode->i_flock list
+ * FIXME: should use a spinlock, once lockd and ceph are ready.
+ */
+void lock_flocks(void)
+{
+        lock_kernel();
+}
+EXPORT_SYMBOL_GPL(lock_flocks);
+
+void unlock_flocks(void)
+{
+        unlock_kernel();
+}
+EXPORT_SYMBOL_GPL(unlock_flocks);
+
 static struct kmem_cache *filelock_cache __read_mostly;
 
 /* Allocate an empty lock structure. */
@@ -511,9 +527,9 @@ static void __locks_delete_block(struct file_lock *waiter)
  */
 static void locks_delete_block(struct file_lock *waiter)
 {
-        lock_kernel();
+        lock_flocks();
         __locks_delete_block(waiter);
-        unlock_kernel();
+        unlock_flocks();
 }
 
 /* Insert waiter into blocker's block list.
@@ -644,7 +660,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 {
         struct file_lock *cfl;
 
-        lock_kernel();
+        lock_flocks();
         for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
                 if (!IS_POSIX(cfl))
                         continue;
@@ -657,7 +673,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
                         fl->fl_pid = pid_vnr(cfl->fl_nspid);
         } else
                 fl->fl_type = F_UNLCK;
-        unlock_kernel();
+        unlock_flocks();
         return;
 }
 EXPORT_SYMBOL(posix_test_lock);
@@ -730,18 +746,16 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
         int error = 0;
         int found = 0;
 
-        lock_kernel();
-        if (request->fl_flags & FL_ACCESS)
-                goto find_conflict;
-
-        if (request->fl_type != F_UNLCK) {
-                error = -ENOMEM;
+        if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {
                 new_fl = locks_alloc_lock();
-                if (new_fl == NULL)
-                        goto out;
-                error = 0;
+                if (!new_fl)
+                        return -ENOMEM;
         }
 
+        lock_flocks();
+        if (request->fl_flags & FL_ACCESS)
+                goto find_conflict;
+
         for_each_lock(inode, before) {
                 struct file_lock *fl = *before;
                 if (IS_POSIX(fl))
@@ -767,8 +781,11 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
          * If a higher-priority process was blocked on the old file lock,
          * give it the opportunity to lock the file.
          */
-        if (found)
+        if (found) {
+                unlock_flocks();
                 cond_resched();
+                lock_flocks();
+        }
 
 find_conflict:
         for_each_lock(inode, before) {
@@ -794,7 +811,7 @@ find_conflict:
         error = 0;
 
 out:
-        unlock_kernel();
+        unlock_flocks();
         if (new_fl)
                 locks_free_lock(new_fl);
         return error;
@@ -823,7 +840,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                 new_fl2 = locks_alloc_lock();
         }
 
-        lock_kernel();
+        lock_flocks();
         if (request->fl_type != F_UNLCK) {
                 for_each_lock(inode, before) {
                         fl = *before;
@@ -991,7 +1008,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
                 locks_wake_up_blocks(left);
         }
  out:
-        unlock_kernel();
+        unlock_flocks();
         /*
          * Free any unused locks.
          */
@@ -1066,14 +1083,14 @@ int locks_mandatory_locked(struct inode *inode)
         /*
          * Search the lock list for this inode for any POSIX locks.
          */
-        lock_kernel();
+        lock_flocks();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (!IS_POSIX(fl))
                         continue;
                 if (fl->fl_owner != owner)
                         break;
         }
-        unlock_kernel();
+        unlock_flocks();
         return fl ? -EAGAIN : 0;
 }
 
@@ -1186,7 +1203,7 @@ int __break_lease(struct inode *inode, unsigned int mode)
 
         new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
 
-        lock_kernel();
+        lock_flocks();
 
         time_out_leases(inode);
 
@@ -1247,8 +1264,10 @@ restart:
                         break_time++;
         }
         locks_insert_block(flock, new_fl);
+        unlock_flocks();
         error = wait_event_interruptible_timeout(new_fl->fl_wait,
                                                 !new_fl->fl_next, break_time);
+        lock_flocks();
         __locks_delete_block(new_fl);
         if (error >= 0) {
                 if (error == 0)
@@ -1263,7 +1282,7 @@ restart:
         }
 
 out:
-        unlock_kernel();
+        unlock_flocks();
         if (!IS_ERR(new_fl))
                 locks_free_lock(new_fl);
         return error;
@@ -1319,7 +1338,7 @@ int fcntl_getlease(struct file *filp)
         struct file_lock *fl;
         int type = F_UNLCK;
 
-        lock_kernel();
+        lock_flocks();
         time_out_leases(filp->f_path.dentry->d_inode);
         for (fl = filp->f_path.dentry->d_inode->i_flock; fl && IS_LEASE(fl);
                         fl = fl->fl_next) {
@@ -1328,7 +1347,7 @@ int fcntl_getlease(struct file *filp)
                         break;
                 }
         }
-        unlock_kernel();
+        unlock_flocks();
         return type;
 }
 
@@ -1341,7 +1360,7 @@ int fcntl_getlease(struct file *filp)
  *      The (input) flp->fl_lmops->fl_break function is required
  *      by break_lease().
  *
- *      Called with kernel lock held.
+ *      Called with file_lock_lock held.
  */
 int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
 {
@@ -1436,7 +1455,15 @@ out:
 }
 EXPORT_SYMBOL(generic_setlease);
 
- /**
+static int __vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
+{
+        if (filp->f_op && filp->f_op->setlease)
+                return filp->f_op->setlease(filp, arg, lease);
+        else
+                return generic_setlease(filp, arg, lease);
+}
+
+/**
  *      vfs_setlease        -       sets a lease on an open file
  *      @filp: file pointer
  *      @arg: type of lease to obtain
@@ -1467,12 +1494,9 @@ int vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
 {
         int error;
 
-        lock_kernel();
-        if (filp->f_op && filp->f_op->setlease)
-                error = filp->f_op->setlease(filp, arg, lease);
-        else
-                error = generic_setlease(filp, arg, lease);
-        unlock_kernel();
+        lock_flocks();
+        error = __vfs_setlease(filp, arg, lease);
+        unlock_flocks();
 
         return error;
 }
@@ -1499,9 +1523,9 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
         if (error)
                 return error;
 
-        lock_kernel();
+        lock_flocks();
 
-        error = vfs_setlease(filp, arg, &flp);
+        error = __vfs_setlease(filp, arg, &flp);
         if (error || arg == F_UNLCK)
                 goto out_unlock;
 
@@ -1516,7 +1540,7 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 
         error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
 out_unlock:
-        unlock_kernel();
+        unlock_flocks();
         return error;
 }
 
@@ -2020,7 +2044,7 @@ void locks_remove_flock(struct file *filp)
                         fl.fl_ops->fl_release_private(&fl);
         }
 
-        lock_kernel();
+        lock_flocks();
         before = &inode->i_flock;
 
         while ((fl = *before) != NULL) {
@@ -2038,7 +2062,7 @@ void locks_remove_flock(struct file *filp)
                 }
                 before = &fl->fl_next;
         }
-        unlock_kernel();
+        unlock_flocks();
 }
 
 /**
@@ -2053,12 +2077,12 @@ posix_unblock_lock(struct file *filp, struct file_lock *waiter)
 {
         int status = 0;
 
-        lock_kernel();
+        lock_flocks();
         if (waiter->fl_next)
                 __locks_delete_block(waiter);
         else
                 status = -ENOENT;
-        unlock_kernel();
+        unlock_flocks();
         return status;
 }
 
@@ -2172,7 +2196,7 @@ static int locks_show(struct seq_file *f, void *v)
 
 static void *locks_start(struct seq_file *f, loff_t *pos)
 {
-        lock_kernel();
+        lock_flocks();
         f->private = (void *)1;
         return seq_list_start(&file_lock_list, *pos);
 }
@@ -2184,7 +2208,7 @@ static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
 
 static void locks_stop(struct seq_file *f, void *v)
 {
-        unlock_kernel();
+        unlock_flocks();
 }
 
 static const struct seq_operations locks_seq_operations = {
@@ -2231,7 +2255,7 @@ int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
 {
         struct file_lock *fl;
         int result = 1;
-        lock_kernel();
+        lock_flocks();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (IS_POSIX(fl)) {
                         if (fl->fl_type == F_RDLCK)
@@ -2248,7 +2272,7 @@ int lock_may_read(struct inode *inode, loff_t start, unsigned long len)
                 result = 0;
                 break;
         }
-        unlock_kernel();
+        unlock_flocks();
         return result;
 }
 
@@ -2271,7 +2295,7 @@ int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
 {
         struct file_lock *fl;
         int result = 1;
-        lock_kernel();
+        lock_flocks();
         for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
                 if (IS_POSIX(fl)) {
                         if ((fl->fl_end < start) || (fl->fl_start > (start + len)))
@@ -2286,7 +2310,7 @@ int lock_may_write(struct inode *inode, loff_t start, unsigned long len)
                 result = 0;
                 break;
         }
-        unlock_kernel();
+        unlock_flocks();
         return result;
 }