On Fri, Feb 23, 2018 at 11:42:34AM -0800, Yang Shi wrote: > > > 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.
Maybe. But you need to explain why there is no backtrace several lines later: access_remote_vm __access_remote_vm down_read(&mm->mmap_sem)