linux/fs/proc
Pavel Emelyanov cf7b708c8d Make access to task's nsproxy lighter
When someone wants to deal with some other taks's namespaces it has to lock
the task and then to get the desired namespace if the one exists.  This is
slow on read-only paths and may be impossible in some cases.

E.g.  Oleg recently noticed a race between unshare() and the (sent for
review in cgroups) pid namespaces - when the task notifies the parent it
has to know the parent's namespace, but taking the task_lock() is
impossible there - the code is under write locked tasklist lock.

On the other hand switching the namespace on task (daemonize) and releasing
the namespace (after the last task exit) is rather rare operation and we
can sacrifice its speed to solve the issues above.

The access to other task namespaces is proposed to be performed
like this:

     rcu_read_lock();
     nsproxy = task_nsproxy(tsk);
     if (nsproxy != NULL) {
             / *
               * work with the namespaces here
               * e.g. get the reference on one of them
               * /
     } / *
         * NULL task_nsproxy() means that this task is
         * almost dead (zombie)
         * /
     rcu_read_unlock();

This patch has passed the review by Eric and Oleg :) and,
of course, tested.

[clg@fr.ibm.com: fix unshare()]
[ebiederm@xmission.com: Update get_net_ns_by_pid]
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-10-19 11:53:37 -07:00
..
array.c pid namespaces: round up the API 2007-10-19 11:53:37 -07:00
base.c Make access to task's nsproxy lighter 2007-10-19 11:53:37 -07:00
generic.c Group short-lived and reclaimable kernel allocations 2007-10-16 09:43:00 -07:00
inode-alloc.txt Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
inode.c SLAB_PANIC more (proc, posix-timers, shmem) 2007-10-17 08:42:47 -07:00
internal.h [NET]: Make /proc/net per network namespace 2007-10-10 16:49:06 -07:00
kcore.c [PATCH] elf: fix kcore note size calculation 2006-12-07 08:39:38 -08:00
kmsg.c [PATCH] Make most file operations structs in fs/ const 2006-03-28 09:16:06 -08:00
Makefile [NET]: Make /proc/net per network namespace 2007-10-10 16:49:06 -07:00
mmu.c fs/proc/mmu.c: headers butchery 2007-10-17 08:42:48 -07:00
nommu.c [PATCH] mark struct file_operations const 6 2007-02-12 09:48:45 -08:00
proc_devtree.c [POWERPC] Make struct property's value a void * 2007-04-13 03:55:18 +10:00
proc_misc.c pid namespaces: define and use task_active_pid_ns() wrapper 2007-10-19 11:53:37 -07:00
proc_net.c [NETNS]: Move some code into __init section when CONFIG_NET_NS=n 2007-10-10 16:54:58 -07:00
proc_sysctl.c Remove redundant check from proc_sys_setattr() 2007-05-08 11:15:10 -07:00
proc_tty.c Make /proc/tty/drivers use seq_list_xxx helpers 2007-07-16 09:05:42 -07:00
root.c [NET]: Make /proc/net per network namespace 2007-10-10 16:49:06 -07:00
task_mmu.c proc: maps protection 2007-05-08 11:15:02 -07:00
task_nommu.c proc: maps protection 2007-05-08 11:15:02 -07:00
vmcore.c [PATCH] i386: Allow i386 crash kernels to handle x86_64 dumps 2007-05-02 19:27:09 +02:00