[Bug 99684] New: [BDW] use-after-free in gen8_ppgtt_alloc_page_directories

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99684

            Bug ID: 99684
           Summary: [BDW] use-after-free in
                    gen8_ppgtt_alloc_page_directories
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: matthew.auld at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 129346
  --> https://bugs.freedesktop.org/attachment.cgi?id=129346&action=edit
dmesg

It looks like we are hitting a use-after-free in
gen8_ppgtt_alloc_page_directories with some pdp state. One possible theory from
looking at the log is that the shrinker kicks in and starts swinging its axe,
evicting one or more vma's, which results in said pdp being freed, I guess we
didn't have anything else inserted in that range, which is why it was freed.
But all of this could have happened while we were in the middle of allocating a
va range for another vma which just so happens to touch the same pdp, and so
with a little bad timing the free could have happened just after we check if we
need to allocate a new pdp, resulting in all kinds of brokenness. It looks like
something similar could also happen with a pd.

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