Re: [PATCH] Make cgroup_path() RCU-safe

[Li Zefan]

Paul Menage wrote:
> Make cgroup_path() RCU safe
> 
> This patch fixes races between /proc/sched_debug by freeing
> cgroup objects via an RCU callback. Thus any cgroup reference obtained
> from an RCU-safe source will remain valid during the RCU section. Since
> dentries are also RCU-safe, this allows us to traverse up the tree safely.
> 
> Additionally, make cgroup_path() check for a NULL cgrp->dentry to avoid
> trying to report a path for a partially-created cgroup.
> 
> Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
> 

Thanks!

Reviewed-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
Tested-by: Li Zefan <lizf@xxxxxxxxxxxxxx>

But the patch is word wrapped..

> --
> 
> There are more RCU changes that I can make for 2.6.29+, but this
> should fix the problem in 2.6.28

...

> +/*
> + * cgroup_path() fills in a filesystem-like path for the given cgroup
> + * into "buf", up to "buflen" characters. Should be called with
> + * cgroup_mutex held, or else in an RCU section with an RCU-protected
> + * cgroup reference
> + */

minor comment:

We already have kernel-doc for cgroup_path(), why do we need those comments
in cgroup.h.

>  int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
> 
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