On Tue, Aug 30, 2016 at 02:50:21PM -0400, Richard Guy Briggs wrote: > On 2016-08-23 16:20, Mateusz Guzik wrote: > > audit_exe_compare directly accesses mm->exe_file without making sure the > > object is stable. Fixing it using current primitives results in > > partially duplicating what proc_exe_link is doing. > > > > As such, introduce a trivial helper which can be used in both places and > > fix the func. > > > > Changes since v1: > > * removed an unused 'out' label which crept in > > > > Mateusz Guzik (2): > > mm: introduce get_task_exe_file > > audit: fix exe_file access in audit_exe_compare > > The task_lock affects a much bigger struct than the mm ref count. Is > this really necessary? Is a spin-lock significantly lower cost than a > refcount? Other than that, this refactorization looks sensible. >
proc_exe_link was taking the lock anyway to guarantee a stable mm. I think the helper cleans the code up a little bit and there is microoptimisation to not play with the refcount. If audit_exe_compare has guarantees the task wont reach exit_mm, it can use get_mm_exe_file which means the atomic op would be only on the file object. I was under the impression this is the expected behaviour, but your patch used the task lock to grab mm, so I mimicked it here. -- Mateusz Guzik
