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pidns: Make the pidns proc mount/umount logic obvious.

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Track the number of pids in the proc hash table.  When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.

Move the mount of proc into alloc_pid when we allocate the pid for
init.

Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task.  Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.

Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue.  This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.

In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <[email protected]> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.

Acked-by: "Serge E. Hallyn" <[email protected]>
Signed-off-by: "Eric W. Biederman" <[email protected]>
This commit is contained in:
Eric W. Biederman 2012-08-01 10:33:47 -07:00
commit 0a01f2cc39
6 changed files with 26 additions and 22 deletions
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4
fs/proc/base.c
View file

@ -2590,10 +2590,6 @@ void proc_flush_task(struct task_struct *task)
proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
tgid->numbers[i].nr);
}
upid = &pid->numbers[pid->level];
if (upid->nr == 1)
pid_ns_release_proc(upid->ns);
}
static struct dentry *proc_pid_instantiate(struct inode *dir,

5
fs/proc/root.c
View file

@ -155,11 +155,6 @@ void __init proc_root_init(void)
err = register_filesystem(&proc_fs_type);
if (err)
return;
err = pid_ns_prepare_proc(&init_pid_ns);
if (err) {
unregister_filesystem(&proc_fs_type);
return;
}
proc_self_init();
proc_symlink("mounts", NULL, "self/mounts");