Fix select on /proc files without ->poll

Taneli Vähäkangas <vahakang@cs.helsinki.fi> reported that commit
786d7e1612f0b0adb6046f19b906609e4fe8b1ba aka "Fix rmmod/read/write races
in /proc entries" broke SBCL + SLIME combo.

The old code in do_select() used DEFAULT_POLLMASK, if couldn't find
->poll handler.  The new code makes ->poll always there and returns 0 by
default, which is not correct.  Return DEFAULT_POLLMASK instead.

Steps to reproduce:

	install emacs, SBCL, SLIME
	emacs
	M-x slime	in *inferior-lisp* buffer
	[watch it doing "Connecting to Swank on port X.."]

Please, apply before 2.6.23.

P.S.: why SBCL can't just read(2) /proc/cpuinfo is a mystery.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: T Taneli Vahakangas <vahakang@cs.helsinki.fi>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 4 insertions, 3 deletions

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index a5b0dfd89a17..0e4d37c93eea 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -11,6 +11,7 @@
 #include <linux/string.h>
 #include <linux/stat.h>
 #include <linux/completion.h>
+#include <linux/poll.h>
 #include <linux/file.h>
 #include <linux/limits.h>
 #include <linux/init.h>
@@ -232,7 +233,7 @@ static ssize_t proc_reg_write(struct file *file, const char __user *buf, size_t
 static unsigned int proc_reg_poll(struct file *file, struct poll_table_struct *pts)
 {
         struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
-        unsigned int rv = 0;
+        unsigned int rv = DEFAULT_POLLMASK;
         unsigned int (*poll)(struct file *, struct poll_table_struct *);
 
         spin_lock(&pde->pde_unload_lock);
diff --git a/fs/select.c b/fs/select.c
index a974082b0824..46dca31c607a 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -26,8 +26,6 @@
 
 #include <asm/uaccess.h>
 
-#define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
-
 struct poll_table_page {
         struct poll_table_page * next;
         struct poll_table_entry * entry;
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 27690798623f..16d813b364ef 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -21,6 +21,8 @@
 #define WQUEUES_STACK_ALLOC     (MAX_STACK_ALLOC - FRONTEND_STACK_ALLOC)
 #define N_INLINE_POLL_ENTRIES   (WQUEUES_STACK_ALLOC / sizeof(struct poll_table_entry))
 
+#define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
+
 struct poll_table_struct;
 
 /*