Re: [PATCH] fs: proc: use down_read_killable in proc_pid_cmdline_read()

[Yang Shi]

On 2/23/18 11:33 AM, Alexey Dobriyan wrote:
> On Wed, Feb 21, 2018 at 03:13:10PM -0800, Yang Shi wrote:
>
> > > > > 2) access_remote_vm() et al will do the same ->mmap_sem, and
> > > > Yes, it does. But, __access_remote_vm() is called by access_process_vm()
> > > > too, which is used by much more places, i.e. ptrace, so I was not sure
> > > > if it is preferred to convert to killable version. So, I leave it untouched.
> > > Yeah, but ->mmap_sem is taken 3 times per /proc/*/cmdline read
> > > and your scalability tests should trigger next backtrace right away.
> > Yes, however, I didn't run into it if mmap_sem is acquired earlier.
> >
> > How about defining a killable version, like
> > __access_remote_vm_killable() which use down_read_killable(), then the
> > killable version can be used by proc/*/cmdline? There might be other
> > users in the future.
> It would be a disaster as interfaces multiply.

Might be not that bad. Just need add:

__access_remote_vm_killable()
access_remote_vm_killable()

Then access_process_vm() keep using __access_remote_vm(). And, use 
access_remote_vm_killable() in fs/proc/base. And, it looks the 
access_process_vm() calls in get_cmdline() can be changed to 
access_remote_vm() (non killable version).

Yang