Messages in this thread | | | Date | Mon, 14 Aug 2023 17:58:17 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kernel/fork: stop playing lockless games for exe_file replacement |
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On 08/14, David Hildenbrand wrote: > > >OK, I seem to understand... without mmap_read_lock() it is possible that > > > > - dup_mm_exe_file() sees mm->exe_file = old_exe_file > > > > - replace_mm_exe_file() does allow_write_access(old_exe_file) > > > > - another process does get_write_access(old_exe_file) > > > > - dup_mm_exe_file()->deny_write_access() fails > > > >Right? > > From what I recall, yes.
Thanks! but then... David, this all is subjective, feel free to ignore, but the current code doesn't look good to me, I mean the purpose of mmap_read_lock() is very unclear. To me something like
if (old_exe_file) { /* * Ensure that if we race with dup_mm_exe_file() and it sees * mm->exe_file == old_exe_file deny_write_access(old_exe_file) * can't fail after we do allow_write_access() and another task * does get_write_access(old_exe_file). */ mmap_read_lock(mm); mmap_read_unlock(mm);
allow_write_access(old_exe_file); fput(old_exe_file); }
looks more understandable...
But this patch from Mateusz looks even better to me. So, FWIW,
Acked-by: Oleg Nesterov <oleg@redhat.com>
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