On Wed, Jul 5, 2023 at 1:37 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 05.07.23 22:25, Peter Xu wrote: > > On Wed, Jul 05, 2023 at 10:22:27AM -0700, Suren Baghdasaryan wrote: > >> On Wed, Jul 5, 2023 at 10:16 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > >>> > >>> On 05.07.23 19:12, Suren Baghdasaryan wrote: > >>>> A memory corruption was reported in [1] with bisection pointing to the > >>>> patch [2] enabling per-VMA locks for x86. > >>>> Disable per-VMA locks config to prevent this issue while the problem is > >>>> being investigated. This is expected to be a temporary measure. > >>>> > >>>> [1] https://bugzilla.kernel.org/show_bug.cgi?id=217624 > >>>> [2] https://lore.kernel.org/all/20230227173632.3292573-30-surenb@xxxxxxxxxx > >>>> > >>>> Reported-by: Jiri Slaby <jirislaby@xxxxxxxxxx> > >>>> Closes: https://lore.kernel.org/all/dbdef34c-3a07-5951-e1ae-e9c6e3cdf51b@xxxxxxxxxx/ > >>>> Reported-by: Jacob Young <jacobly.alt@xxxxxxxxx> > >>>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217624 > >>>> Fixes: 0bff0aaea03e ("x86/mm: try VMA lock-based page fault handling first") > >>>> Cc: stable@xxxxxxxxxxxxxxx > >>>> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > >>>> --- > >>>> mm/Kconfig | 3 ++- > >>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/mm/Kconfig b/mm/Kconfig > >>>> index 09130434e30d..0abc6c71dd89 100644 > >>>> --- a/mm/Kconfig > >>>> +++ b/mm/Kconfig > >>>> @@ -1224,8 +1224,9 @@ config ARCH_SUPPORTS_PER_VMA_LOCK > >>>> def_bool n > >>>> > >>>> config PER_VMA_LOCK > >>>> - def_bool y > >>>> + bool "Enable per-vma locking during page fault handling." > >>>> depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP > >>>> + depends on BROKEN > >>>> help > >>>> Allow per-vma locking during page fault handling. > >>>> > >>> Do we have any testing results (that don't reveal other issues :) ) for > >>> patch #1? Not sure if we really want to mark it broken if patch #1 fixes > >>> the issue. > >> > >> I tested the fix using the only reproducer provided in the reports > >> plus kernel compilation and my fork stress test. All looked good and > >> stable but I don't know if other reports had the same issue or > >> something different. > > > > The commit log seems slightly confusing. It mostly says the bug was still > > not solved, but I assume patch 1 is the current "fix", it's just not clear > > whether there's any other potential issues? > > > > According to the stable tree rules: > > > > - It must fix a problem that causes a build error (but not for things > > marked CONFIG_BROKEN), an oops, a hang, data corruption, a real > > security issue, or some "oh, that's not good" issue. In short, something > > critical. > > > > I think it means vma lock will never be fixed in 6.4, and it can't (because > > after this patch it'll be BROKEN, and this patch copies stable, and we > > can't fix BROKEN things in stables). > > > > Totally no problem I see, just to make sure this is what you wanted.. > > > > There'll still try to be a final fix, am I right? As IIRC allowing page > > faults during fork() is one of the major goals of vma lock. > > At least not that I am aware of (and people who care about that should > really work on scalable fork() alternatives, like that io_uring fork() > thingy). > > My understanding is that CONFIG_PER_VMA_LOCK wants to speed up page > concurrent page faults *after* fork() [or rather, after new process > creation], IOW, when we have a lot of mmap() activity going on while > some threads of the new process are already active and don't actually > touch what's getting newly mmaped. Getting as much concurrency as we can is the goal. If we can allow some page faults during fork, I would take that too. But for now let's deploy the simplest and safest approach. > > -- > Cheers, > > David / dhildenb >
