Re: [RFC] sys_setrlimit() in 2.6.16
- From: Andrew Morton <akpm@xxxxxxxx>
- Date: Thu, 16 Feb 2006 00:58:26 -0800
Cliff Wickman <cpw@xxxxxxx> wrote:
A test suite uncovered a possible bug in setrlimit(2), in 2.6.16-rc3.
A code that does
mylimits.rlim_cur = 0;
setrlimit(RLIMIT_CPU, &mylimits);
does not set a cpu time limit.
No signal is sent to this code when its "limit" of 0 seconds expires.
Whereas, under the 2.6.5 kernel (SuSE SLESS9) a signal was sent.
I don't see any obvious difference in sys_setrlimit() or
set_process_cpu_timer() between 2.6.5 and 2.6.16.
Is this a correction, or a bug?
Is a cpu time limit of 0 supposed to limit a task to 0 seconds, or
leave it unlimited?
This has to be considered a bug. The spec certainly implies that a limit
of zero should be honoured and, probably more importantly, that's how it
works in 2.4.
Problem is, the code in there all assumes that an it_prof_expires of zero
means "it was never set", and changing that (add a yes-it-has flag?) would
be less than trivial.
So I think the path of least resistance here is to just convert the
caller's zero seconds into one second. That in fact gives the same
behaviour as 2.4: you get whacked after one second or more CPU time.
(This is not a final patch - that revolting expression in sys_setrlimit()
needs help first).
diff -puN kernel/sys.c~a kernel/sys.c
--- devel/kernel/sys.c~a 2006-02-16 00:42:49.000000000 -0800
+++ devel-akpm/kernel/sys.c 2006-02-16 00:45:10.000000000 -0800
@@ -1657,7 +1657,19 @@ asmlinkage long sys_setrlimit(unsigned i
(cputime_eq(current->signal->it_prof_expires, cputime_zero) ||
new_rlim.rlim_cur <= cputime_to_secs(
current->signal->it_prof_expires))) {
- cputime_t cputime = secs_to_cputime(new_rlim.rlim_cur);
+ unsigned long rlim_cur = new_rlim.rlim_cur;
+ cputime_t cputime;
+
+ if (rlim_cur == 0) {
+ /*
+ * The caller is asking for an immediate RLIMIT_CPU
+ * expiry. But we use the zero value to mean "it was
+ * never set". So let's cheat and make it one second
+ * instead
+ */
+ rlim_cur = 1;
+ }
+ cputime = secs_to_cputime(rlim_cur);
read_lock(&tasklist_lock);
spin_lock_irq(¤t->sighand->siglock);
set_process_cpu_timer(current, CPUCLOCK_PROF,
_
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