commit b835996f628eadb55c5fb222ba46fe9395bf73c7
author Dipankar Sarma <dipankar@in.ibm.com> Fri Sep 09 13:04:14 2005 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> Fri Sep 09 13:57:55 2005 -0700
tree d63d80585d197e1ffc299af4a0034049790fb197
parent ab2af1f5005069321c5d130f09cce577b03f43ef

[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>

fs/select.c

diff --git a/fs/select.c b/fs/select.c
index 2e56325..f10a103 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 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 @@
 		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 @@
 	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) {