SEND_SIG_NOINFO: Set si_pid to tgid instead of pid

From: Sukadev Bhattiprolu <[email protected]>
Date: Tue, 16 Dec 2008 17:07:17 -0800
Subject: [PATCH] SEND_SIG_NOINFO: Set si_pid to tgid instead of pid

POSIX requires the si_pid to be the process id of the sender, so ->si_pid should really be set to 'tgid'. This change does have following changes in behavior:

- When sending pdeath_signal on re-parent to a sub-thread, ->si_pid cannot be used to identify the thread that did the re-parent since it will now show the tgid instead of thread id.

- A multi-threaded application that expects to find the specific thread that encountered a SIGPIPE using the ->si_pid will now break.

---
 kernel/signal.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index d11e5f8..700d767 100644
@@ -856,7 +856,7 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
 			q->info.si_signo = sig;
 			q->info.si_errno = 0;
 			q->info.si_code = SI_USER;
-			q->info.si_pid = task_pid_nr_ns(current,
+			q->info.si_pid = task_tgid_nr_ns(current,
 							task_active_pid_ns(t));
 			q->info.si_uid = current_uid();
 			break;

1.5.2.5

Arguably these deserve a heads-up to linux-abi, not that whether si_pid was tid or tgid was probably actually documented before (and I presume the wrong-namespace issue just doesn't need to be).

Thanks,
Roland

Ccing linux-api for the user-visible changes per Roland's suggestion. Not sure if the current behavior is documented somewhere. but should the new behavior be documented in pipe(7) and prctl(2) ?

This patch was recently added to -mm tree.

Sukadev

Sukadev Bhattiprolu [[email protected]] wrote:

| 
| From: Sukadev Bhattiprolu <[email protected]>
| Date: Tue, 16 Dec 2008 17:07:17 -0800
| Subject: [PATCH] SEND_SIG_NOINFO: Set si_pid to tgid instead of pid
| 
| POSIX requires the si_pid to be the process id of the sender, so ->si_pid
| should really be set to 'tgid'. This change does have following changes
| in behavior:
| 
| 	- When sending pdeath_signal on re-parent to a sub-thread, ->si_pid
| 	  cannot be used to identify the thread that did the re-parent since
| 	  it will now show the tgid instead of thread id.
| 
| 	- A multi-threaded application that expects to find the specific
| 	  thread that encountered a SIGPIPE using the ->si_pid will now
| 	  break.
| 
| Signed-off-by: Sukadev Bhattiprolu <[email protected]>
| ---
|  kernel/signal.c |    2 +-
|  1 files changed, 1 insertions(+), 1 deletions(-)
| 
| diff --git a/kernel/signal.c b/kernel/signal.c
| index d11e5f8..700d767 100644
| --- a/kernel/signal.c
| +++ b/kernel/signal.c
| @@ -856,7 +856,7 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
|  			q->info.si_signo = sig;
|  			q->info.si_errno = 0;
|  			q->info.si_code = SI_USER;
| -			q->info.si_pid = task_pid_nr_ns(current,
| +			q->info.si_pid = task_tgid_nr_ns(current,
|  							task_active_pid_ns(t));
|  			q->info.si_uid = current_uid();
|  			break;
| -- 
| 1.5.2.5
| 
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