linux-kernel - Re: [PATCH v3 1/1] waitid: Add support for waiting for the current process group

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Message-ID: <20190814205040.d7shwe6u3jz6qmcc@wittgenstein>
Date:   Wed, 14 Aug 2019 22:50:41 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, libc-alpha@...rceware.org,
        alistair23@...il.com, ebiederm@...ssion.com, arnd@...db.de,
        dalias@...c.org, torvalds@...ux-foundation.org,
        adhemerval.zanella@...aro.org, fweimer@...hat.com,
        palmer@...ive.com, macro@....com, zongbox@...il.com,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk, hpa@...or.com
Subject: Re: [PATCH v3 1/1] waitid: Add support for waiting for the current
 process group

On Wed, Aug 14, 2019 at 06:09:17PM +0200, Oleg Nesterov wrote:
> On 08/14, Christian Brauner wrote:
> >
> > and a signal could come in between the system call that
> > retrieved the process gorup and the call to waitid that changes the
>                         ^^^^^
> > current process group.
> 
> I noticed this typo only because I spent 2 minutes or more trying to
> understand this sentence ;) But yes, a signal handler or another thread
> can change pgrp in between.
> 
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>

Applied-to:
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=pidfd
on top of P_PIDFD changes (cf. [1]) with merge conflict resolved (cf. [2]).
(All changes on top of v5.3-rc1.)

Merged-into:
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=for-next
and should show up in linux-next tomorrow.

Thanks!
Christian

/* References */
[1]: https://lore.kernel.org/r/20190727222229.6516-2-christian@brauner.io
[2]: patch after resolved merge-conflict:
 kernel/exit.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 64bb6893a37d..d2d74a7b81d1 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1596,10 +1596,13 @@ static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 		break;
 	case P_PGID:
 		type = PIDTYPE_PGID;
-		if (upid <= 0)
+		if (upid < 0)
 			return -EINVAL;
 
-		pid = find_get_pid(upid);
+		if (upid)
+			pid = find_get_pid(upid);
+		else
+			pid = get_task_pid(current, PIDTYPE_PGID);
 		break;
 	case P_PIDFD:
 		type = PIDTYPE_PID;