Oleg Nesterov [oleg@xxxxxxxxxx] 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@xxxxxxxxxx> Use task_pid() to get leader's 'struct pid' and avoid the find_pid(). Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx> Acked-by: Pavel Emelianov <xemul@xxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Cc: Cedric Le Goater <clg@xxxxxxxxxx> Cc: Dave Hansen <haveblue@xxxxxxxxxx> Cc: Serge Hallyn <serue@xxxxxxxxxx> Cc: Herbert Poetzel <herbert@xxxxxxxxxxxx> --- 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); _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers