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![David Rientjes](/assets/img/avatar_default.png)
Commit 4d4bbd8526
("mm, oom_reaper: skip mm structs with mmu
notifiers") prevented the oom reaper from unmapping private anonymous
memory with the oom reaper when the oom victim mm had mmu notifiers
registered.
The rationale is that doing mmu_notifier_invalidate_range_{start,end}()
around the unmap_page_range(), which is needed, can block and the oom
killer will stall forever waiting for the victim to exit, which may not
be possible without reaping.
That concern is real, but only true for mmu notifiers that have
blockable invalidate_range_{start,end}() callbacks. This patch adds a
"flags" field to mmu notifier ops that can set a bit to indicate that
these callbacks do not block.
The implementation is steered toward an expensive slowpath, such as
after the oom reaper has grabbed mm->mmap_sem of a still alive oom
victim.
[rientjes@google.com: mmu_notifier_invalidate_range_end() can also call the invalidate_range() must not block, fix comment]
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1801091339570.240101@chino.kir.corp.google.com
[akpm@linux-foundation.org: make mm_has_blockable_invalidate_notifiers() return bool, use rwsem_is_locked()]
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1712141329500.74052@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
426 lines
12 KiB
C
426 lines
12 KiB
C
/*
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* linux/mm/mmu_notifier.c
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*
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* Copyright (C) 2008 Qumranet, Inc.
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* Copyright (C) 2008 SGI
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* Christoph Lameter <cl@linux.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*/
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#include <linux/rculist.h>
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#include <linux/mmu_notifier.h>
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/err.h>
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#include <linux/srcu.h>
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#include <linux/rcupdate.h>
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#include <linux/sched.h>
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#include <linux/sched/mm.h>
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#include <linux/slab.h>
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/* global SRCU for all MMs */
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DEFINE_STATIC_SRCU(srcu);
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/*
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* This function allows mmu_notifier::release callback to delay a call to
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* a function that will free appropriate resources. The function must be
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* quick and must not block.
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*/
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void mmu_notifier_call_srcu(struct rcu_head *rcu,
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void (*func)(struct rcu_head *rcu))
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{
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call_srcu(&srcu, rcu, func);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
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void mmu_notifier_synchronize(void)
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{
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/* Wait for any running method to finish. */
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srcu_barrier(&srcu);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
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/*
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* This function can't run concurrently against mmu_notifier_register
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* because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
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* runs with mm_users == 0. Other tasks may still invoke mmu notifiers
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* in parallel despite there being no task using this mm any more,
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* through the vmas outside of the exit_mmap context, such as with
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* vmtruncate. This serializes against mmu_notifier_unregister with
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* the mmu_notifier_mm->lock in addition to SRCU and it serializes
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* against the other mmu notifiers with SRCU. struct mmu_notifier_mm
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* can't go away from under us as exit_mmap holds an mm_count pin
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* itself.
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*/
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void __mmu_notifier_release(struct mm_struct *mm)
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{
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struct mmu_notifier *mn;
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int id;
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/*
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* SRCU here will block mmu_notifier_unregister until
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* ->release returns.
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*/
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
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/*
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* If ->release runs before mmu_notifier_unregister it must be
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* handled, as it's the only way for the driver to flush all
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* existing sptes and stop the driver from establishing any more
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* sptes before all the pages in the mm are freed.
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*/
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if (mn->ops->release)
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mn->ops->release(mn, mm);
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spin_lock(&mm->mmu_notifier_mm->lock);
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while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
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mn = hlist_entry(mm->mmu_notifier_mm->list.first,
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struct mmu_notifier,
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hlist);
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/*
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* We arrived before mmu_notifier_unregister so
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* mmu_notifier_unregister will do nothing other than to wait
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* for ->release to finish and for mmu_notifier_unregister to
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* return.
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*/
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hlist_del_init_rcu(&mn->hlist);
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}
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spin_unlock(&mm->mmu_notifier_mm->lock);
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srcu_read_unlock(&srcu, id);
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/*
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* synchronize_srcu here prevents mmu_notifier_release from returning to
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* exit_mmap (which would proceed with freeing all pages in the mm)
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* until the ->release method returns, if it was invoked by
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* mmu_notifier_unregister.
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*
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* The mmu_notifier_mm can't go away from under us because one mm_count
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* is held by exit_mmap.
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*/
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synchronize_srcu(&srcu);
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}
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/*
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* If no young bitflag is supported by the hardware, ->clear_flush_young can
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* unmap the address and return 1 or 0 depending if the mapping previously
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* existed or not.
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*/
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int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->clear_flush_young)
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young |= mn->ops->clear_flush_young(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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int __mmu_notifier_clear_young(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->clear_young)
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young |= mn->ops->clear_young(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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int __mmu_notifier_test_young(struct mm_struct *mm,
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unsigned long address)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->test_young) {
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young = mn->ops->test_young(mn, mm, address);
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if (young)
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break;
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}
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
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pte_t pte)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->change_pte)
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mn->ops->change_pte(mn, mm, address, pte);
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}
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srcu_read_unlock(&srcu, id);
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}
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void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->invalidate_range_start)
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mn->ops->invalidate_range_start(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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}
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EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_start);
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void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
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unsigned long start,
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unsigned long end,
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bool only_end)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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/*
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* Call invalidate_range here too to avoid the need for the
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* subsystem of having to register an invalidate_range_end
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* call-back when there is invalidate_range already. Usually a
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* subsystem registers either invalidate_range_start()/end() or
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* invalidate_range(), so this will be no additional overhead
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* (besides the pointer check).
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*
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* We skip call to invalidate_range() if we know it is safe ie
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* call site use mmu_notifier_invalidate_range_only_end() which
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* is safe to do when we know that a call to invalidate_range()
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* already happen under page table lock.
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*/
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if (!only_end && mn->ops->invalidate_range)
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mn->ops->invalidate_range(mn, mm, start, end);
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if (mn->ops->invalidate_range_end)
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mn->ops->invalidate_range_end(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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}
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EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range_end);
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void __mmu_notifier_invalidate_range(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->invalidate_range)
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mn->ops->invalidate_range(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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}
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EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
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/*
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* Must be called while holding mm->mmap_sem for either read or write.
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* The result is guaranteed to be valid until mm->mmap_sem is dropped.
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*/
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bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
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{
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struct mmu_notifier *mn;
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int id;
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bool ret = false;
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WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
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if (!mm_has_notifiers(mm))
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return ret;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (!mn->ops->invalidate_range &&
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!mn->ops->invalidate_range_start &&
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!mn->ops->invalidate_range_end)
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continue;
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if (!(mn->ops->flags & MMU_INVALIDATE_DOES_NOT_BLOCK)) {
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ret = true;
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break;
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}
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}
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srcu_read_unlock(&srcu, id);
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return ret;
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}
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static int do_mmu_notifier_register(struct mmu_notifier *mn,
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struct mm_struct *mm,
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int take_mmap_sem)
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{
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struct mmu_notifier_mm *mmu_notifier_mm;
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int ret;
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BUG_ON(atomic_read(&mm->mm_users) <= 0);
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ret = -ENOMEM;
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mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
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if (unlikely(!mmu_notifier_mm))
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goto out;
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if (take_mmap_sem)
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down_write(&mm->mmap_sem);
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ret = mm_take_all_locks(mm);
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if (unlikely(ret))
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goto out_clean;
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if (!mm_has_notifiers(mm)) {
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INIT_HLIST_HEAD(&mmu_notifier_mm->list);
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spin_lock_init(&mmu_notifier_mm->lock);
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mm->mmu_notifier_mm = mmu_notifier_mm;
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mmu_notifier_mm = NULL;
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}
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mmgrab(mm);
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/*
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* Serialize the update against mmu_notifier_unregister. A
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* side note: mmu_notifier_release can't run concurrently with
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* us because we hold the mm_users pin (either implicitly as
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* current->mm or explicitly with get_task_mm() or similar).
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* We can't race against any other mmu notifier method either
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* thanks to mm_take_all_locks().
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*/
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spin_lock(&mm->mmu_notifier_mm->lock);
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hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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mm_drop_all_locks(mm);
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out_clean:
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if (take_mmap_sem)
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up_write(&mm->mmap_sem);
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kfree(mmu_notifier_mm);
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out:
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BUG_ON(atomic_read(&mm->mm_users) <= 0);
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return ret;
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}
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/*
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* Must not hold mmap_sem nor any other VM related lock when calling
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* this registration function. Must also ensure mm_users can't go down
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* to zero while this runs to avoid races with mmu_notifier_release,
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* so mm has to be current->mm or the mm should be pinned safely such
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* as with get_task_mm(). If the mm is not current->mm, the mm_users
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* pin should be released by calling mmput after mmu_notifier_register
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* returns. mmu_notifier_unregister must be always called to
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* unregister the notifier. mm_count is automatically pinned to allow
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* mmu_notifier_unregister to safely run at any time later, before or
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* after exit_mmap. ->release will always be called before exit_mmap
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* frees the pages.
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*/
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int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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return do_mmu_notifier_register(mn, mm, 1);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_register);
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/*
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* Same as mmu_notifier_register but here the caller must hold the
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* mmap_sem in write mode.
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*/
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int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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return do_mmu_notifier_register(mn, mm, 0);
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}
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EXPORT_SYMBOL_GPL(__mmu_notifier_register);
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/* this is called after the last mmu_notifier_unregister() returned */
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void __mmu_notifier_mm_destroy(struct mm_struct *mm)
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{
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BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
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kfree(mm->mmu_notifier_mm);
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mm->mmu_notifier_mm = LIST_POISON1; /* debug */
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}
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/*
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* This releases the mm_count pin automatically and frees the mm
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* structure if it was the last user of it. It serializes against
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* running mmu notifiers with SRCU and against mmu_notifier_unregister
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* with the unregister lock + SRCU. All sptes must be dropped before
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* calling mmu_notifier_unregister. ->release or any other notifier
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* method may be invoked concurrently with mmu_notifier_unregister,
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* and only after mmu_notifier_unregister returned we're guaranteed
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* that ->release or any other method can't run anymore.
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*/
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void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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BUG_ON(atomic_read(&mm->mm_count) <= 0);
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if (!hlist_unhashed(&mn->hlist)) {
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/*
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* SRCU here will force exit_mmap to wait for ->release to
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* finish before freeing the pages.
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*/
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int id;
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id = srcu_read_lock(&srcu);
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/*
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* exit_mmap will block in mmu_notifier_release to guarantee
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* that ->release is called before freeing the pages.
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*/
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if (mn->ops->release)
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mn->ops->release(mn, mm);
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srcu_read_unlock(&srcu, id);
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spin_lock(&mm->mmu_notifier_mm->lock);
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/*
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* Can not use list_del_rcu() since __mmu_notifier_release
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* can delete it before we hold the lock.
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*/
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hlist_del_init_rcu(&mn->hlist);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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}
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/*
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* Wait for any running method to finish, of course including
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* ->release if it was run by mmu_notifier_release instead of us.
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*/
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synchronize_srcu(&srcu);
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BUG_ON(atomic_read(&mm->mm_count) <= 0);
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mmdrop(mm);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
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/*
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* Same as mmu_notifier_unregister but no callback and no srcu synchronization.
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*/
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void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
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struct mm_struct *mm)
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{
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spin_lock(&mm->mmu_notifier_mm->lock);
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/*
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* Can not use list_del_rcu() since __mmu_notifier_release
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* can delete it before we hold the lock.
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*/
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hlist_del_init_rcu(&mn->hlist);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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BUG_ON(atomic_read(&mm->mm_count) <= 0);
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mmdrop(mm);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
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