Re: [PATCH] pidfd: Stop taking cred_guard_mutex

[Christian Brauner]

On Tue, Mar 10, 2020 at 01:52:05PM -0500, Eric W. Biederman wrote:
> 
> During exec some file descriptors are closed and the files struct is
> unshared.  But all of that can happen at other times and it has the
> same protections during exec as at ordinary times.  So stop taking the
> cred_guard_mutex as it is useless.
> 
> Furthermore he cred_guard_mutex is a bad idea because it is deadlock
> prone, as it is held in serveral while waiting possibly indefinitely
> for userspace to do something.
> 
> Cc: Sargun Dhillon <sargun@xxxxxxxxx>
> Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> ---
>  kernel/pid.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> Christian if you don't have any objections I will take this one through
> my tree.

Sure.
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

> 
> I tried to figure out why this code path takes the cred_guard_mutex and
> the archive on lore.kernel.org was not helpful in finding that part of
> the conversation.

Let me think a little harder and hopefully get back to you with a
sensible explanation.