Re: [PATCH 2.4.22-pre1][NET] timer cleanups

From: Vinay K Nallamothu
Date: Mon Sep 01 2003 - 09:01:34 EST


Hi Dave,

On Sun, 2003-08-31 at 09:03, David S. Miller wrote:
> On Sat, 30 Aug 2003 21:11:37 +0530
> Vinay K Nallamothu <vinay-rc@xxxxxxxxxxxxxx> wrote:
>
> > This patch does the following timer code cleanup:
> >
> > 1. Change del_timer/add_timer to mod_timer
> > 2. Use static timer initialisation wherever applicable
>
> I'm not accepting this. In particular, the ip6_flowlabel.c
> change is a bad idea because the code remains racey.


> Someone
> submitted a similar move to mod_timer() for ip6_flowlabel
That too was submitted by me. Unfortunately I never got to see your
mail. No excuses though.


>
> Just blindly doing these kinds of conversions to mod_timer()
> is foolhardy. You need to apply some brains to it to make
> sure you really are getting rid of whatever potential races
> exist in the code.
You are correct. While I tried to make sure that new bugs are not
introduced, I haven't paid attention to the existing ones.

> And in the ip6_flowlabel.c case things are
> as buggy as they were before.

Please find the updated patch below and let me know if it's ok.

Thanks
Vinay

ip6_flowlabel.c:
1. Use static timer initializer
2. Use timer macros to handle jiffie wrap in comparisions
3. Convert del_timer/add_timer to mod_timer

ip6_flowlabel.c | 30 ++++++++++++++++--------------
1 files changed, 16 insertions(+), 14 deletions(-)

diff -urN linux-2.4.22/net/ipv6/ip6_flowlabel.c linux-2.4.22-nvk/net/ipv6/ip6_flowlabel.c
--- linux-2.4.22/net/ipv6/ip6_flowlabel.c 2003-06-14 10:03:12.000000000 +0530
+++ linux-2.4.22-nvk/net/ipv6/ip6_flowlabel.c 2003-09-01 16:47:03.000000000 +0530
@@ -48,7 +48,8 @@
static atomic_t fl_size = ATOMIC_INIT(0);
static struct ip6_flowlabel *fl_ht[FL_HASH_MASK+1];

-static struct timer_list ip6_fl_gc_timer;
+static void ip6_fl_gc(unsigned long dummy);
+static struct timer_list ip6_fl_gc_timer = TIMER_INITIALIZER(ip6_fl_gc, 0, 0);

/* FL hash table lock: it protects only of GC */

@@ -92,10 +93,12 @@

static void fl_release(struct ip6_flowlabel *fl)
{
+ write_lock_bh(&ip6_fl_lock);
+
fl->lastuse = jiffies;
if (atomic_dec_and_test(&fl->users)) {
unsigned long ttd = fl->lastuse + fl->linger;
- if ((long)(ttd - fl->expires) > 0)
+ if (time_after(ttd, fl->expires))
fl->expires = ttd;
ttd = fl->expires;
if (fl->opt && fl->share == IPV6_FL_S_EXCL) {
@@ -103,11 +106,12 @@
fl->opt = NULL;
kfree(opt);
}
- if (!del_timer(&ip6_fl_gc_timer) ||
- (long)(ip6_fl_gc_timer.expires - ttd) > 0)
- ip6_fl_gc_timer.expires = ttd;
- add_timer(&ip6_fl_gc_timer);
+ if (!timer_pending(&ip6_fl_gc_timer) ||
+ time_after(ip6_fl_gc_timer.expires, ttd))
+ mod_timer(&ip6_fl_gc_timer, ttd);
}
+
+ write_unlock_bh(&ip6_fl_lock);
}

static void ip6_fl_gc(unsigned long dummy)
@@ -124,16 +128,16 @@
while ((fl=*flp) != NULL) {
if (atomic_read(&fl->users) == 0) {
unsigned long ttd = fl->lastuse + fl->linger;
- if ((long)(ttd - fl->expires) > 0)
+ if (time_after(ttd, fl->expires))
fl->expires = ttd;
ttd = fl->expires;
- if ((long)(now - ttd) >= 0) {
+ if (time_after_eq(now, ttd)) {
*flp = fl->next;
fl_free(fl);
atomic_dec(&fl_size);
continue;
}
- if (!sched || (long)(ttd - sched) < 0)
+ if (!sched || time_before(ttd, sched))
sched = ttd;
}
flp = &fl->next;
@@ -262,11 +266,11 @@
if (!expires)
return -EPERM;
fl->lastuse = jiffies;
- if (fl->linger < linger)
+ if (time_before(fl->linger, linger))
fl->linger = linger;
- if (expires < fl->linger)
+ if (time_before(expires, fl->linger))
expires = fl->linger;
- if ((long)(fl->expires - (fl->lastuse+expires)) < 0)
+ if (time_before(fl->expires, fl->lastuse + expires))
fl->expires = fl->lastuse + expires;
return 0;
}
@@ -609,8 +613,6 @@

void ip6_flowlabel_init()
{
- init_timer(&ip6_fl_gc_timer);
- ip6_fl_gc_timer.function = ip6_fl_gc;
#ifdef CONFIG_PROC_FS
create_proc_read_entry("net/ip6_flowlabel", 0, 0, ip6_fl_read_proc, NULL);
#endif


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