[PATCH] files: lock-free fd look-up

With the use of RCU in files structure, the look-up of files using fds can now
be lock-free.  The lookup is protected by rcu_read_lock()/rcu_read_unlock().
This patch changes the readers to use lock-free lookup.

Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Ravikiran Thirumalai <kiran_th@gmail.com>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 27 insertions, 19 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index d2f3ed8acd93..863b46e0d78a 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -40,10 +40,10 @@ static inline int get_close_on_exec(unsigned int fd)
         struct files_struct *files = current->files;
         struct fdtable *fdt;
         int res;
-        spin_lock(&files->file_lock);
+        rcu_read_lock();
         fdt = files_fdtable(files);
         res = FD_ISSET(fd, fdt->close_on_exec);
-        spin_unlock(&files->file_lock);
+        rcu_read_unlock();
         return res;
 }
 
diff --git a/fs/proc/base.c b/fs/proc/base.c
index d0087a0b024b..23db452ab428 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -62,6 +62,7 @@
 #include <linux/namespace.h>
 #include <linux/mm.h>
 #include <linux/smp_lock.h>
+#include <linux/rcupdate.h>
 #include <linux/kallsyms.h>
 #include <linux/mount.h>
 #include <linux/security.h>
@@ -283,16 +284,16 @@ static int proc_fd_link(struct inode *inode, struct dentry **dentry, struct vfsm
 
         files = get_files_struct(task);
         if (files) {
-                spin_lock(&files->file_lock);
+                rcu_read_lock();
                 file = fcheck_files(files, fd);
                 if (file) {
                         *mnt = mntget(file->f_vfsmnt);
                         *dentry = dget(file->f_dentry);
-                        spin_unlock(&files->file_lock);
+                        rcu_read_unlock();
                         put_files_struct(files);
                         return 0;
                 }
-                spin_unlock(&files->file_lock);
+                rcu_read_unlock();
                 put_files_struct(files);
         }
         return -ENOENT;
@@ -1062,7 +1063,7 @@ static int proc_readfd(struct file * filp, void * dirent, filldir_t filldir)
                         files = get_files_struct(p);
                         if (!files)
                                 goto out;
-                        spin_lock(&files->file_lock);
+                        rcu_read_lock();
                         fdt = files_fdtable(files);
                         for (fd = filp->f_pos-2;
                              fd < fdt->max_fds;
@@ -1071,7 +1072,7 @@ static int proc_readfd(struct file * filp, void * dirent, filldir_t filldir)
 
                                 if (!fcheck_files(files, fd))
                                         continue;
-                                spin_unlock(&files->file_lock);
+                                rcu_read_unlock();
 
                                 j = NUMBUF;
                                 i = fd;
@@ -1083,12 +1084,12 @@ static int proc_readfd(struct file * filp, void * dirent, filldir_t filldir)
 
                                 ino = fake_ino(tid, PROC_TID_FD_DIR + fd);
                                 if (filldir(dirent, buf+j, NUMBUF-j, fd+2, ino, DT_LNK) < 0) {
-                                        spin_lock(&files->file_lock);
+                                        rcu_read_lock();
                                         break;
                                 }
-                                spin_lock(&files->file_lock);
+                                rcu_read_lock();
                         }
-                        spin_unlock(&files->file_lock);
+                        rcu_read_unlock();
                         put_files_struct(files);
         }
 out:
@@ -1263,9 +1264,9 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
 
         files = get_files_struct(task);
         if (files) {
-                spin_lock(&files->file_lock);
+                rcu_read_lock();
                 if (fcheck_files(files, fd)) {
-                        spin_unlock(&files->file_lock);
+                        rcu_read_unlock();
                         put_files_struct(files);
                         if (task_dumpable(task)) {
                                 inode->i_uid = task->euid;
@@ -1277,7 +1278,7 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
                         security_task_to_inode(task, inode);
                         return 1;
                 }
-                spin_unlock(&files->file_lock);
+                rcu_read_unlock();
                 put_files_struct(files);
         }
         d_drop(dentry);
@@ -1369,7 +1370,7 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
         if (!files)
                 goto out_unlock;
         inode->i_mode = S_IFLNK;
-        spin_lock(&files->file_lock);
+        rcu_read_lock();
         file = fcheck_files(files, fd);
         if (!file)
                 goto out_unlock2;
@@ -1377,7 +1378,7 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
                 inode->i_mode |= S_IRUSR | S_IXUSR;
         if (file->f_mode & 2)
                 inode->i_mode |= S_IWUSR | S_IXUSR;
-        spin_unlock(&files->file_lock);
+        rcu_read_unlock();
         put_files_struct(files);
         inode->i_op = &proc_pid_link_inode_operations;
         inode->i_size = 64;
@@ -1387,7 +1388,7 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
         return NULL;
 
 out_unlock2:
-        spin_unlock(&files->file_lock);
+        rcu_read_unlock();
         put_files_struct(files);
 out_unlock:
         iput(inode);
diff --git a/fs/select.c b/fs/select.c
index 2e56325c73c4..f10a10317d54 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -22,6 +22,7 @@
 #include <linux/personality.h> /* for STICKY_TIMEOUTS */
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/rcupdate.h>
 
 #include <asm/uaccess.h>
 
@@ -185,9 +186,9 @@ int do_select(int n, fd_set_bits *fds, long *timeout)
         int retval, i;
         long __timeout = *timeout;
 
-        spin_lock(&current->files->file_lock);
+        rcu_read_lock();
         retval = max_select_fd(n, fds);
-        spin_unlock(&current->files->file_lock);
+        rcu_read_unlock();
 
         if (retval < 0)
                 return retval;
@@ -329,8 +330,10 @@ sys_select(int n, fd_set __user *inp, fd_set __user *outp, fd_set __user *exp, s
                 goto out_nofds;
 
         /* max_fdset can increase, so grab it once to avoid race */
+        rcu_read_lock();
         fdt = files_fdtable(current->files);
         max_fdset = fdt->max_fdset;
+        rcu_read_unlock();
         if (n > max_fdset)
                 n = max_fdset;
 
@@ -469,10 +472,14 @@ asmlinkage long sys_poll(struct pollfd __user * ufds, unsigned int nfds, long ti
         struct poll_list *head;
         struct poll_list *walk;
         struct fdtable *fdt;
+        int max_fdset;
 
         /* Do a sanity check on nfds ... */
+        rcu_read_lock();
         fdt = files_fdtable(current->files);
-        if (nfds > fdt->max_fdset && nfds > OPEN_MAX)
+        max_fdset = fdt->max_fdset;
+        rcu_read_unlock();
+        if (nfds > max_fdset && nfds > OPEN_MAX)
                 return -EINVAL;
 
         if (timeout) {