[PATCH] signal: improve warning about using SI_TKILL in rt_[tg]sigqueueinfo

[Vladimir Davydov <vdavydov@parallels.com>]

Sending SI_TKILL from rt_[tg]sigqueueinfo was deprecated, so now we
issue a warning on the first attempt of doing it. We use WARN_ON_ONCE,
which is not informative and, what is worse, taints the kernel, making
the trinity syscall fuzzer complain false-positively from time to time.

This patch therefore substitutes the WARN_ON_ONCE with a pr_warn_once.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
---
 kernel/signal.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index a390499943e4..3cbcd94457af 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2993,8 +2993,11 @@ static int do_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t *info)
 	 */
 	if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
 	    (task_pid_vnr(current) != pid)) {
-		/* We used to allow any < 0 si_code */
-		WARN_ON_ONCE(info->si_code < 0);
+		/* We used to allow SI_TKILL */
+		if (info->si_code == SI_TKILL)
+			pr_warn_once("%s (%d): Sending SI_TKILL from "
+				     "rt_sigqueueinfo is deprecated\n",
+				     current->comm, current->pid);
 		return -EPERM;
 	}
 	info->si_signo = sig;
@@ -3041,10 +3044,13 @@ static int do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
 	/* Not even root can pretend to send signals from the kernel.
 	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
 	 */
-	if (((info->si_code >= 0 || info->si_code == SI_TKILL)) &&
+	if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
 	    (task_pid_vnr(current) != pid)) {
-		/* We used to allow any < 0 si_code */
-		WARN_ON_ONCE(info->si_code < 0);
+		/* We used to allow SI_TKILL */
+		if (info->si_code == SI_TKILL)
+			pr_warn_once("%s (%d): Sending SI_TKILL from "
+				     "rt_tgsigqueueinfo is deprecated\n",
+				     current->comm, current->pid);
 		return -EPERM;
 	}
 	info->si_signo = sig;
-- 
1.7.10.4