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


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