mm/oom_kill.c: add task UID to info message on an oom kill

In the event of an oom kill, useful information about the killed process
is printed to dmesg.  Users, especially system administrators, will find
it useful to immediately see the UID of the process.

We already print uid when dumping eligible tasks so it is not overly hard
to find that information in the oom report.  However this information is
unavailable when dumping of eligible tasks is disabled.

In the following example, abuse_the_ram is the name of a program that
attempts to iteratively allocate all available memory until it is stopped
by force.

Current message:

Out of memory: Killed process 35389 (abuse_the_ram)
total-vm:133718232kB, anon-rss:129624980kB, file-rss:0kB,
shmem-rss:0kB

Patched message:

Out of memory: Killed process 2739 (abuse_the_ram),
total-vm:133880028kB, anon-rss:129754836kB, file-rss:0kB,
shmem-rss:0kB, UID:0

[akpm@linux-foundation.org: s/UID %d/UID:%u/ in printk]
Link: http://lkml.kernel.org/r/1560362273-534-1-git-send-email-jsavitz@redhat.com
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Suggested-by: David Rientjes <rientjes@google.com>
Acked-by: Rafael Aquini <aquini@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -884,12 +884,13 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 	 */
 	do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
 	mark_oom_victim(victim);
-	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
+	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u\n",
 		message, task_pid_nr(victim), victim->comm,
 		K(victim->mm->total_vm),
 		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
 		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
-		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
+		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)),
+		from_kuid(&init_user_ns, task_uid(victim)));
 	task_unlock(victim);
 
 	/*