[PATCH] RLIMIT_CPU: fix handling of a zero limit

At present the kernel doesn't honour an attempt to set RLIMIT_CPU to zero
seconds.  But the spec says it should, and that's what 2.4.x does.

Fixing this for real would involve some complexity (such as adding a new
it-has-been-set flag to the task_struct, and testing that everwhere, instead
of overloading the value of it_prof_expires).

Given that a 2.4 kernel won't actually send the signal until one second has
expired anyway, let's just handle this case by treating the caller's
zero-seconds as one second.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ulrich Weigand <uweigand@de.ibm.com>
Cc: Cliff Wickman <cpw@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sys.c b/kernel/sys.c
index f91218a..105e102 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1657,7 +1657,19 @@ asmlinkage long sys_setrlimit(unsigned int resource, struct rlimit __user *rlim)
            (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(&current->sighand->siglock);
                set_process_cpu_timer(current, CPUCLOCK_PROF,