fix setpriority(PRIO_PGRP) thread iterator breakage

When user calls sys_setpriority(PRIO_PGRP ...) on a NPTL style multi-LWP
process, only the task leader of the process is affected, all other
sibling LWP threads didn't receive the setting.  The problem was that the
iterator used in sys_setpriority() only iteartes over one task for each
process, ignoring all other sibling thread.

Introduce a new macro do_each_pid_thread / while_each_pid_thread to walk
each thread of a process.  Convert 4 call sites in {set/get}priority and
ioprio_{set/get}.

Signed-off-by: Ken Chen <kenchen@google.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ioprio.c

@@ -115,11 +115,11 @@ asmlinkage long sys_ioprio_set(int which, int who, int ioprio)
 				pgrp = task_pgrp(current);
 			else
 				pgrp = find_vpid(who);
-			do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 				ret = set_task_ioprio(p, ioprio);
 				if (ret)
 					break;
-			} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 			break;
 		case IOPRIO_WHO_USER:
 			if (!who)
@@ -204,7 +204,7 @@ asmlinkage long sys_ioprio_get(int which, int who)
 				pgrp = task_pgrp(current);
 			else
 				pgrp = find_vpid(who);
-			do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 				tmpio = get_task_ioprio(p);
 				if (tmpio < 0)
 					continue;
@@ -212,7 +212,7 @@ asmlinkage long sys_ioprio_get(int which, int who)
 					ret = tmpio;
 				else
 					ret = ioprio_best(ret, tmpio);
-			} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 			break;
 		case IOPRIO_WHO_USER:
 			if (!who)

include/linux/pid.h

@@ -161,4 +161,13 @@ pid_t pid_vnr(struct pid *pid);
 			}						\
 	} while (0)
 
+#define do_each_pid_thread(pid, type, task)				\
+	do_each_pid_task(pid, type, task) {				\
+		struct task_struct *tg___ = task;			\
+		do {
+
+#define while_each_pid_thread(pid, type, task)				\
+		} while_each_thread(tg___, task);			\
+		task = tg___;						\
+	} while_each_pid_task(pid, type, task)
 #endif /* _LINUX_PID_H */

kernel/sys.c

@@ -169,9 +169,9 @@ asmlinkage long sys_setpriority(int which, int who, int niceval)
 				pgrp = find_vpid(who);
 			else
 				pgrp = task_pgrp(current);
-			do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 				error = set_one_prio(p, niceval, error);
-			} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 			break;
 		case PRIO_USER:
 			user = current->user;
@@ -229,11 +229,11 @@ asmlinkage long sys_getpriority(int which, int who)
 				pgrp = find_vpid(who);
 			else
 				pgrp = task_pgrp(current);
-			do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
 				niceval = 20 - task_nice(p);
 				if (niceval > retval)
 					retval = niceval;
-			} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
 			break;
 		case PRIO_USER:
 			user = current->user;