[PATCH] mm: Remove pointless might_sleep() in remove_vm_area().

[Tetsuo Handa]

Thomas Hellstrom wrote:
> So to summarize. Yes, the drm callers can be fixed up, but IMO requiring
> vfree() to be non-atomic is IMO not a good idea if avoidable.

I agree.

I don't know about drm code. But I can find AppArmor code doing
kvfree() from dfa_free() from aa_dfa_free_kref() from kref_put() from
aa_put_dfa() from aa_free_profile() which says

 * If the profile was referenced from a task context, free_profile() will
 * be called from an rcu callback routine, so we must not sleep here.

which means that below changes broke things without properly auditing
all vfree()/kvfree() users.

  commit bf22e37a641327e3 ("mm: add vfree_atomic()")
  commit 0f110a9b956c1678 ("kernel/fork: use vfree_atomic() to free thread stack")
  commit 8d5341a6260a59cf ("x86/ldt: use vfree_atomic() to free ldt entries")
  commit 5803ed292e63a1bf ("mm: mark all calls into the vmalloc subsystem as potentially sleeping")
  commit f9e09977671b618a ("mm: turn vmap_purge_lock into a mutex")
  commit 763b218ddfaf5676 ("mm: add preempt points into __purge_vmap_area_lazy()")

Since above commits did not take appropriate proceedure for changing
non-blocking API to blocking API, we must fix vfree() part for 4.10 and 4.11.

Updated patch is at
http://lkml.kernel.org/r/201703271916.FBI69340.SQFtOFVJHOLOMF@I-love.SAKURA.ne.jp .