linux-kernel - [PATCH] Fix select on /proc files without ->poll

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Date:	Wed, 5 Sep 2007 21:56:11 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	akpm@...l.org
Cc:	linux-kernel@...r.kernel.org,
	T Taneli Vahakangas <vahakang@...helsinki.fi>
Subject: [PATCH] Fix select on /proc files without ->poll

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

Old code in do_select() used DEFAULT_POLLMASK, if couldn't find ->poll
handler. 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@...il.com>
---

 fs/proc/inode.c      |    3 ++-
 fs/select.c          |    2 --
 include/linux/poll.h |    2 ++
 3 files changed, 4 insertions(+), 3 deletions(-)

--- 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);
--- 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;
--- 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;
 
 /* 
-
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