| Message ID | alpine.LSU.2.11.2008141503370.18085@eggly.anvils (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | khugepaged: adjust VM_BUG_ON_MM() in __khugepaged_enter() | expand |
On Fri, Aug 14, 2020 at 3:13 PM Hugh Dickins <hughd@google.com> wrote: > > syzbot crashes on the VM_BUG_ON_MM(khugepaged_test_exit(mm), mm) in > __khugepaged_enter(): yes, when one thread is about to dump core, has set > core_state, and is waiting for others, another might do something calling > __khugepaged_enter(), which now crashes because I lumped the core_state > test (known as "mmget_still_valid") into khugepaged_test_exit(). I still > think it's best to lump them together, so just in this exceptional case, > check mm->mm_users directly instead of khugepaged_test_exit(). > > Reported-by: syzbot <syzkaller@googlegroups.com> > Fixes: bbe98f9cadff ("khugepaged: khugepaged_test_exit() check mmget_still_valid()") > Signed-off-by: Hugh Dickins <hughd@google.com> > Cc: stable@vger.kernel.org # v4.8+ Acked-by: Yang Shi <shy828301@gmail.com> > --- > > mm/khugepaged.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- v5.9-rc/mm/khugepaged.c 2020-08-12 19:46:50.867196579 -0700 > +++ linux/mm/khugepaged.c 2020-08-14 14:24:32.739457309 -0700 > @@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct > return -ENOMEM; > > /* __khugepaged_exit() must not run from under us */ > - VM_BUG_ON_MM(khugepaged_test_exit(mm), mm); > + VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm); > if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { > free_mm_slot(mm_slot); > return 0; >
--- v5.9-rc/mm/khugepaged.c 2020-08-12 19:46:50.867196579 -0700 +++ linux/mm/khugepaged.c 2020-08-14 14:24:32.739457309 -0700 @@ -466,7 +466,7 @@ int __khugepaged_enter(struct mm_struct return -ENOMEM; /* __khugepaged_exit() must not run from under us */ - VM_BUG_ON_MM(khugepaged_test_exit(mm), mm); + VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm); if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { free_mm_slot(mm_slot); return 0;
syzbot crashes on the VM_BUG_ON_MM(khugepaged_test_exit(mm), mm) in __khugepaged_enter(): yes, when one thread is about to dump core, has set core_state, and is waiting for others, another might do something calling __khugepaged_enter(), which now crashes because I lumped the core_state test (known as "mmget_still_valid") into khugepaged_test_exit(). I still think it's best to lump them together, so just in this exceptional case, check mm->mm_users directly instead of khugepaged_test_exit(). Reported-by: syzbot <syzkaller@googlegroups.com> Fixes: bbe98f9cadff ("khugepaged: khugepaged_test_exit() check mmget_still_valid()") Signed-off-by: Hugh Dickins <hughd@google.com> Cc: stable@vger.kernel.org # v4.8+ --- mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)