Re: [patch] sys_epoll_wait() timeout saga ...

[Andrew Morton]

Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote:
>
> The attached patch uses the kernel min() macro, that is optimized has 
>  single compare by gcc-O2. Andrew, this goes over (hopefully ;) the bits 
>  you already have in -mm.

OK, well I've rather lost the plot with all the patches flying around.

I now have one single patch against epoll.c, below.  Please confirm that
this is what was intended.   If not, I'll drop it and let's start again.





From: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>

The sys_epoll_wait() function was not handling correctly negative timeouts
(besides -1), and like sys_poll(), was comparing millisec to secs in
testing the upper timeout limit.

Signed-off-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 fs/eventpoll.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff -puN fs/eventpoll.c~sys_epoll_wait-fix-handling-of-negative-timeouts fs/eventpoll.c
--- devel/fs/eventpoll.c~sys_epoll_wait-fix-handling-of-negative-timeouts	2005-09-24 23:01:00.000000000 -0700
+++ devel-akpm/fs/eventpoll.c	2005-09-24 23:02:50.000000000 -0700
@@ -101,6 +101,10 @@
 /* Maximum number of poll wake up nests we are allowing */
 #define EP_MAX_POLLWAKE_NESTS 4
 
+/* Maximum msec timeout value storeable in a long int */
+#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, LONG_MAX / HZ - 1000ULL)
+
+
 struct epoll_filefd {
 	struct file *file;
 	int fd;
@@ -1506,8 +1510,8 @@ static int ep_poll(struct eventpoll *ep,
 	 * and the overflow condition. The passed timeout is in milliseconds,
 	 * that why (t * HZ) / 1000.
 	 */
-	jtimeout = timeout == -1 || timeout > (MAX_SCHEDULE_TIMEOUT - 1000) / HZ ?
-		MAX_SCHEDULE_TIMEOUT: (timeout * HZ + 999) / 1000;
+	jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
+		MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
 
 retry:
 	write_lock_irqsave(&ep->lock, flags);
_

-
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