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[Bug 1045340] regression: java segfaults on latest kernels caused by the stack gap fix
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Thu, 22 Jun 2017 07:25:12 +0000
  • Message-id: <bug-1045340-21960-29IeZM1DSK@http.bugzilla.suse.com/>
http://bugzilla.suse.com/show_bug.cgi?id=1045340
http://bugzilla.suse.com/show_bug.cgi?id=1045340#c14

--- Comment #14 from Michal Hocko <mhocko@xxxxxxxx> ---
Thank you Vlastimil! Very helpful. So it doesn't look like an accounting bug
which I was suspecting. I am really surprised the mapping in the middle doesn't
have VM_GROWSDOWN. mprotect should preserve VM_GROWS* flag.

And indeed mprotect does the following
prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
[...]
vm_flags = calc_vm_prot_bits(prot);
[...]
newflags = vm_flags;
newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));

so it should preserve everything but RWX which are taken from the given prot
parameter. Maybe I am missing something though. I will be staring into the code
some more.

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