Messages in this thread Patch in this message | | | Date | Mon, 16 Jul 2007 12:59:52 -0700 | From | sukadev@us ... | Subject | Re: [PATCH 3/5] Use task_pid() to find leader's pid |
| |
Oleg Nesterov [oleg@tv-sign.ru] wrote: | Sukadev Bhattiprolu wrote: | > | > Use task_pid() to get leader's pid since find_pid() cannot be used | > after detach_pid(). See comments in the code below for more details. | > | > ... | > | > + * Note: With multiple pid namespaces, active pid namespace of | > + * a process is stored in its struct pid. The detach_pid | > + * below frees the struct pid, so we will have no notion | > + * of an active pid namespace until we complete the | > + * subsequent attach_pid(). Which means - calls like | > + * find_pid()/pid_to_nr() return NULL and cannot be used | > + * between the detach_pid() and attach_pid() calls. | | I think both the changelog and the comment are confusing, | | > detach_pid(tsk, PIDTYPE_PID); | > tsk->pid = leader->pid; | > - attach_pid(tsk, PIDTYPE_PID, find_pid(tsk->pid)); | > + attach_pid(tsk, PIDTYPE_PID, task_pid(leader)); | | because the change itself looks like an obvious performance fix, even | we don't use multiple pid namespaces. I don't think it is good idea to | add a fat comment which doesn't match the current reality, and find_pid() | should be avoided anyway.
Its a performance fix but also a correctness issue with multiple pid namespaces. Here is the modified patch with the simplified changelog and comment removed.
| | Stupid question: why do we need to put the pid namespace into the struct | pid? Isn't it better if the user of the struct pid should know its ns? | For example, if /proc does put_pid(), that pid should be from the active | namespace.
Not sure I fully understand this. A process, and by extension its 'struct pid' is visible in multiple namespaces and we maintain this list of namespaces in each 'struct pid'.
Are you suggesting having a pid_namespace with a list of all 'struct pids' that are visible in it ?
| | Sukadev, could you cc me if you do that kind of changes?
Sure - I will. ---
Subject: [PATCH 3/5] Use task_pid() to find leader's pid
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Use task_pid() to get leader's 'struct pid' and avoid the find_pid().
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com> Acked-by: Pavel Emelianov <xemul@openvz.org>
Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: Serge Hallyn <serue@us.ibm.com> Cc: Herbert Poetzel <herbert@13thfloor.at> --- fs/exec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Index: lx26-22-rc6-mm1a/fs/exec.c =================================================================== --- lx26-22-rc6-mm1a.orig/fs/exec.c 2007-07-13 18:23:55.000000000 -0700 +++ lx26-22-rc6-mm1a/fs/exec.c 2007-07-16 12:56:22.000000000 -0700 @@ -908,7 +908,7 @@ static int de_thread(struct task_struct */ detach_pid(tsk, PIDTYPE_PID); tsk->pid = leader->pid; - attach_pid(tsk, PIDTYPE_PID, find_pid(tsk->pid)); + attach_pid(tsk, PIDTYPE_PID, task_pid(leader)); transfer_pid(leader, tsk, PIDTYPE_PGID); transfer_pid(leader, tsk, PIDTYPE_SID); list_replace_rcu(&leader->tasks, &tsk->tasks); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |