[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>

1 files changed, 10 insertions, 3 deletions

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) {