Re: [UPDATE PATCH][Bug 5132] fix sys_poll() large timeout handling

[Peter Staubach]

Nishanth Aravamudan wrote:

> I don't think the embedded folks are going to be ok with adding a 64-bit
> div in the poll() common-path... But otherwise the patch looks pretty
> sane, except I think you want s64, not int64_t? I can't ever remember
> myself :)
>  

Oops, I missed an include which is required.  The updated patch is attached.

A 64 bit quantity divided by a 32 bit quantity seems to be a standard
interface in the kernel and is used fairly widely, so I suspect that
the embedded folks have already done the work.

I don't know which should be used, s64 or int64_t.  I chose int64_t
because then it would (more or less) match the interface of do_div().

> I agree the interface mght be mis-defined. And changing timeout_msecs()
> to an integer is consistent with the size of millisecond-unit variables
> used elsewhere in the kernel.

Yes, it also makes the kernel definition for sys_poll() match the user level
definition for poll(2) found in <poll.h>.

   Thanx...

      ps

Signed-off-by: Peter Staubach <staubach@xxxxxxxxxx>
--- linux-2.6.13/fs/select.c.org	2005-08-28 19:41:01.000000000 -0400
+++ linux-2.6.13/fs/select.c	2005-09-12 11:11:53.000000000 -0400
@@ -24,6 +24,7 @@
 #include <linux/fs.h>
 
 #include <asm/uaccess.h>
+#include <asm/div64.h>
 
 #define ROUND_UP(x,y) (((x)+(y)-1)/(y))
 #define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
@@ -457,25 +458,34 @@ static int do_poll(unsigned int nfds,  s
 	return count;
 }
 
-asmlinkage long sys_poll(struct pollfd __user * ufds, unsigned int nfds, long timeout)
+asmlinkage long sys_poll(struct pollfd __user * ufds, unsigned int nfds, int timeout_msecs)
 {
 	struct poll_wqueues table;
  	int fdcount, err;
  	unsigned int i;
 	struct poll_list *head;
  	struct poll_list *walk;
+	long timeout;
+	int64_t lltimeout;
 
 	/* Do a sanity check on nfds ... */
 	if (nfds > current->files->max_fdset && nfds > OPEN_MAX)
 		return -EINVAL;
 
-	if (timeout) {
-		/* Careful about overflow in the intermediate values */
-		if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
-			timeout = (unsigned long)(timeout*HZ+999)/1000+1;
-		else /* Negative or overflow */
+	if (timeout_msecs) {
+		if (timeout_msecs < 0)
 			timeout = MAX_SCHEDULE_TIMEOUT;
-	}
+		else {
+			lltimeout = (int64_t)timeout_msecs * HZ + 999;
+			do_div(lltimeout, 1000);
+			lltimeout++;
+			if (lltimeout > MAX_SCHEDULE_TIMEOUT)
+				timeout = MAX_SCHEDULE_TIMEOUT;
+			else
+				timeout = (long)lltimeout;
+		}
+	} else
+		timeout = 0;
 
 	poll_initwait(&table);
 
--- linux-2.6.13/include/linux/syscalls.h.org	2005-08-28 19:41:01.000000000 -0400
+++ linux-2.6.13/include/linux/syscalls.h	2005-09-12 10:22:25.000000000 -0400
@@ -420,7 +420,7 @@ asmlinkage long sys_socketpair(int, int,
 asmlinkage long sys_socketcall(int call, unsigned long __user *args);
 asmlinkage long sys_listen(int, int);
 asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int nfds,
-				long timeout);
+				int timeout_msecs);
 asmlinkage long sys_select(int n, fd_set __user *inp, fd_set __user *outp,
 			fd_set __user *exp, struct timeval __user *tvp);
 asmlinkage long sys_epoll_create(int size);