Re: [PATCH] pid: restore the old behaviour of the ns_last_pid sysctl

[Oleg Nesterov]

On 11/03, Andrei Vagin wrote:
>
> @@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, 
> int write,
>* it should synchronize its usage with external means.
>*/
>  
> - tmp.data = _ns->idr.idr_next;
> - return proc_dointvec_minmax(, write, buffer, lenp, ppos);
> + next = idr_get_cursor(_ns->idr) - 1;
> +
> + tmp.data = 
> + ret = proc_dointvec_minmax(, write, buffer, lenp, ppos);
> + if (ret < 0)
> + return ret;
> +
> + if (!write)
> + return 0;
> +
> + idr_set_cursor(_ns->idr, next + 1);
> + return 0;

Ah yes, we should also take "write" into account, I forgot it is readable.
Can't resist, to me

err = proc_dointvec_minmax(...);
if (!err && write)
idr_set_cursor(...);

return err;

looks a bit more readable, but this is matter of taste of course.


Acked-by: Oleg Nesterov 

Re: [PATCH] pid: restore the old behaviour of the ns_last_pid sysctl

[Oleg Nesterov]

On 11/03, Andrei Vagin wrote:
>
> @@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, 
> int write,
>* it should synchronize its usage with external means.
>*/
>  
> - tmp.data = _ns->idr.idr_next;
> - return proc_dointvec_minmax(, write, buffer, lenp, ppos);
> + next = idr_get_cursor(_ns->idr) - 1;
> +
> + tmp.data = 
> + ret = proc_dointvec_minmax(, write, buffer, lenp, ppos);
> + if (ret < 0)
> + return ret;
> +
> + if (!write)
> + return 0;
> +
> + idr_set_cursor(_ns->idr, next + 1);
> + return 0;

Ah yes, we should also take "write" into account, I forgot it is readable.
Can't resist, to me

err = proc_dointvec_minmax(...);
if (!err && write)
idr_set_cursor(...);

return err;

looks a bit more readable, but this is matter of taste of course.


Acked-by: Oleg Nesterov 

[PATCH] pid: restore the old behaviour of the ns_last_pid sysctl

[Andrei Vagin]

CRIU uses ns_last_pid to fork a process with a specified pid. For
example, if we need to create a process with the pid of 1,
we write  into /proc/sys/kernel/ns_last_pid

$ echo  > /proc/sys/kernel/ns_last_pid; sh -c 'echo $$'
1

This behaviour has been broken and now if we write  to ns_last_pid,
a process will get the pid . This patch restores the old behaviour.

fixes: ("pid: replace pid bitmap implementation with IDR API")
Cc: Gargi Sharma 
Cc: Oleg Nesterov 
Signed-off-by: Andrei Vagin 
---
 kernel/pid_namespace.c | 15 +--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index fea2c24fa460..504dadb1d920 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -287,6 +287,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int 
write,
 {
struct pid_namespace *pid_ns = task_active_pid_ns(current);
struct ctl_table tmp = *table;
+   int ret, next;
 
if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
@@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int 
write,
 * it should synchronize its usage with external means.
 */
 
-   tmp.data = _ns->idr.idr_next;
-   return proc_dointvec_minmax(, write, buffer, lenp, ppos);
+   next = idr_get_cursor(_ns->idr) - 1;
+
+   tmp.data = 
+   ret = proc_dointvec_minmax(, write, buffer, lenp, ppos);
+   if (ret < 0)
+   return ret;
+
+   if (!write)
+   return 0;
+
+   idr_set_cursor(_ns->idr, next + 1);
+   return 0;
 }
 
 extern int pid_max;
-- 
2.13.6

[PATCH] pid: restore the old behaviour of the ns_last_pid sysctl

[Andrei Vagin]

CRIU uses ns_last_pid to fork a process with a specified pid. For
example, if we need to create a process with the pid of 1,
we write  into /proc/sys/kernel/ns_last_pid

$ echo  > /proc/sys/kernel/ns_last_pid; sh -c 'echo $$'
1

This behaviour has been broken and now if we write  to ns_last_pid,
a process will get the pid . This patch restores the old behaviour.

fixes: ("pid: replace pid bitmap implementation with IDR API")
Cc: Gargi Sharma 
Cc: Oleg Nesterov 
Signed-off-by: Andrei Vagin 
---
 kernel/pid_namespace.c | 15 +--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index fea2c24fa460..504dadb1d920 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -287,6 +287,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int 
write,
 {
struct pid_namespace *pid_ns = task_active_pid_ns(current);
struct ctl_table tmp = *table;
+   int ret, next;
 
if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
@@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int 
write,
 * it should synchronize its usage with external means.
 */
 
-   tmp.data = _ns->idr.idr_next;
-   return proc_dointvec_minmax(, write, buffer, lenp, ppos);
+   next = idr_get_cursor(_ns->idr) - 1;
+
+   tmp.data = 
+   ret = proc_dointvec_minmax(, write, buffer, lenp, ppos);
+   if (ret < 0)
+   return ret;
+
+   if (!write)
+   return 0;
+
+   idr_set_cursor(_ns->idr, next + 1);
+   return 0;
 }
 
 extern int pid_max;
-- 
2.13.6