On Wed, Jul 16, 2025 at 3:50 AM Lorenzo Stoakes <lorenzo.stoa...@oracle.com> wrote: > > On Wed, Jul 16, 2025 at 12:44:23PM +0200, David Hildenbrand wrote: > > On 16.07.25 05:05, Suren Baghdasaryan wrote: > > > The /proc/pid/maps file is generated page by page, with the mmap_lock > > > released between pages. This can lead to inconsistent reads if the > > > underlying vmas are concurrently modified. For instance, if a vma split > > > or merge occurs at a page boundary while /proc/pid/maps is being read, > > > the same vma might be seen twice: once before and once after the change. > > > This duplication is considered acceptable for userspace handling. > > > However, observing a "hole" where a vma should be (e.g., due to a vma > > > being replaced and the space temporarily being empty) is unacceptable. > > > > > > Implement a test that: > > > 1. Forks a child process which continuously modifies its address space, > > > specifically targeting a vma at the boundary between two pages. > > > 2. The parent process repeatedly reads the child's /proc/pid/maps. > > > 3. The parent process checks the last vma of the first page and > > > the first vma of the second page for consistency, looking for the > > > effects of vma splits or merges. > > > > > > The test duration is configurable via the -d command-line parameter > > > in seconds to increase the likelihood of catching the race condition. > > > The default test duration is 5 seconds. > > > > > > Example Command: proc-maps-race -d 10 > > > > > > Signed-off-by: Suren Baghdasaryan <sur...@google.com> > > > > Why is this selftest not making use of any kselftest framework? > > > > I'm sure there is a very good reason :)
It used to be a part of proc-pid-vm.c and after the split I kept its overall structure. I'll look into using the kselftest framework. Thanks! > > > > Reading assert() feels very weird compared to other selftests. > > Sorry to meta-review via your review again David :P > > But just to say tools/testing/selftests/kselftest_harness.h is really good, > and > makes life simple. See tools/testing/selftests/mm/guard-regions.c for an > example > of how they can be used - pretty straightforward and avoids a lot of kselftest > boilerplate. Thanks for the pointers. I need to figure out a way to pass command-line parameters to my test. Maybe I can use fixtures for that... Let me read more about it. > > > > > -- > > Cheers, > > > > David / dhildenb > > > >
