Re: [PATCH] make setpriority POSIX compliant; introduce PRIO_THREAD extension

[Denys Vlasenko <dvlasenk@redhat.com>]

On Tue, 2008-09-09 at 17:45 +0200, Michael Kerrisk wrote:
> > Patch is run tested. I will post test program etc as a reply.
> 
> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com>
> 
> Please do CC me on API changes, so that they might get documented in
> the man pages.
> 
> Thanks for this work.  (I'm not sure whether or not it's a response to
> my bug report, http://bugzilla.kernel.org/show_bug.cgi?id=6258 )

I worked on it because of this bug report:

https://bugzilla.redhat.com/show_bug.cgi?id=455251

> I tested your patch.  Most things seem to work as I would expect, but
> there is one strangeness.
> 
> I would expect
> setpriority(PRIO_PROCESS, getpid())
> and
> setpriority(PRIO_PROCESS, 0)
> to have the same affect (because: which == PRIO_PRCESS, who == 0
> conventionally means "the calling process").
> 
> But they do not: the latter call only changes the priority of the
> calling thread.  Is this intended?

No, it was not intended. I think this error is here:

+               case PRIO_PROCESS:
+                       if (who)
+                               pid = find_vpid(who);
+                       else {
+                               pid = task_pid(current);
+                               who = current->pid;
+                       }

I was confused. ->pid is TID, had to use ->tgid to get PID.
The fix: replace
who = current->pid;
with
who = current->tgid;
There are two places where you need to do it.

Updated patch is below.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
--
vda



diff --git a/include/linux/resource.h b/include/linux/resource.h
index aaa423a..f292690 100644
--- a/include/linux/resource.h
+++ b/include/linux/resource.h
@@ -51,6 +51,7 @@ struct rlimit {
 #define	PRIO_PROCESS	0
 #define	PRIO_PGRP	1
 #define	PRIO_USER	2
+#define	PRIO_THREAD	3
 
 /*
  * Limit the stack by to some sane default: root can always
diff --git a/kernel/sys.c b/kernel/sys.c
index 038a7bc..d339c1a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -142,9 +142,9 @@ asmlinkage long sys_setpriority(int which, int who,
int niceval)
 	struct task_struct *g, *p;
 	struct user_struct *user;
 	int error = -EINVAL;
-	struct pid *pgrp;
+	struct pid *pgrp, *pid;
 
-	if (which > PRIO_USER || which < PRIO_PROCESS)
+	if (which > PRIO_THREAD || which < PRIO_PROCESS)
 		goto out;
 
 	/* normalize: avoid signed division (rounding problems) */
@@ -156,7 +156,7 @@ asmlinkage long sys_setpriority(int which, int who,
int niceval)
 
 	read_lock(&tasklist_lock);
 	switch (which) {
-		case PRIO_PROCESS:
+		case PRIO_THREAD:
 			if (who)
 				p = find_task_by_vpid(who);
 			else
@@ -164,6 +164,19 @@ asmlinkage long sys_setpriority(int which, int who,
int niceval)
 			if (p)
 				error = set_one_prio(p, niceval, error);
 			break;
+		case PRIO_PROCESS:
+			if (who)
+				pid = find_vpid(who);
+			else {
+				pid = task_pid(current);
+				who = current->tgid;
+			}
+			do_each_pid_thread(pid, PIDTYPE_PID, p) {
+				if (who == p->pid || who == p->tgid) {
+					error = set_one_prio(p, niceval, error);
+				}
+			} while_each_pid_thread(pid, PIDTYPE_PID, p);
+			break;
 		case PRIO_PGRP:
 			if (who)
 				pgrp = find_vpid(who);
@@ -206,14 +219,14 @@ asmlinkage long sys_getpriority(int which, int
who)
 	struct task_struct *g, *p;
 	struct user_struct *user;
 	long niceval, retval = -ESRCH;
-	struct pid *pgrp;
+	struct pid *pgrp, *pid;
 
-	if (which > PRIO_USER || which < PRIO_PROCESS)
+	if (which > PRIO_THREAD || which < PRIO_PROCESS)
 		return -EINVAL;
 
 	read_lock(&tasklist_lock);
 	switch (which) {
-		case PRIO_PROCESS:
+		case PRIO_THREAD:
 			if (who)
 				p = find_task_by_vpid(who);
 			else
@@ -224,6 +237,21 @@ asmlinkage long sys_getpriority(int which, int who)
 					retval = niceval;
 			}
 			break;
+		case PRIO_PROCESS:
+			if (who)
+				pid = find_vpid(who);
+			else {
+				pid = task_pid(current);
+				who = current->tgid;
+			}
+			do_each_pid_thread(pid, PIDTYPE_PID, p) {
+				if (who == p->pid || who == p->tgid) {
+					niceval = 20 - task_nice(p);
+					if (niceval > retval)
+						retval = niceval;
+				}
+			} while_each_pid_thread(pid, PIDTYPE_PID, p);
+			break;
 		case PRIO_PGRP:
 			if (who)
 				pgrp = find_vpid(who);