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Subject[PATCH 08/22] mm/hmm: Hold a mmgrab from hmm to mm
Date
From: Jason Gunthorpe <jgg@mellanox.com>

So long as a struct hmm pointer exists, so should the struct mm it is
linked too. Hold the mmgrab() as soon as a hmm is created, and mmdrop() it
once the hmm refcount goes to zero.

Since mmdrop() (ie a 0 kref on struct mm) is now impossible with a !NULL
mm->hmm delete the hmm_hmm_destroy().

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>
---
include/linux/hmm.h | 3 ---
kernel/fork.c | 1 -
mm/hmm.c | 22 ++++------------------
3 files changed, 4 insertions(+), 22 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 1fba6979adf4..1d97b6d62c5b 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -577,14 +577,11 @@ static inline int hmm_vma_fault(struct hmm_mirror *mirror,
}

/* Below are for HMM internal use only! Not to be used by device driver! */
-void hmm_mm_destroy(struct mm_struct *mm);
-
static inline void hmm_mm_init(struct mm_struct *mm)
{
mm->hmm = NULL;
}
#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
-static inline void hmm_mm_destroy(struct mm_struct *mm) {}
static inline void hmm_mm_init(struct mm_struct *mm) {}
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */

diff --git a/kernel/fork.c b/kernel/fork.c
index 75675b9bf6df..c704c3cedee7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -673,7 +673,6 @@ void __mmdrop(struct mm_struct *mm)
WARN_ON_ONCE(mm == current->active_mm);
mm_free_pgd(mm);
destroy_context(mm);
- hmm_mm_destroy(mm);
mmu_notifier_mm_destroy(mm);
check_mm(mm);
put_user_ns(mm->user_ns);
diff --git a/mm/hmm.c b/mm/hmm.c
index 22a97ada108b..080b17a2e87e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -20,6 +20,7 @@
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memremap.h>
+#include <linux/sched/mm.h>
#include <linux/jump_label.h>
#include <linux/dma-mapping.h>
#include <linux/mmu_notifier.h>
@@ -73,6 +74,7 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm)
hmm->notifiers = 0;
hmm->dead = false;
hmm->mm = mm;
+ mmgrab(hmm->mm);

spin_lock(&mm->page_table_lock);
if (!mm->hmm)
@@ -100,6 +102,7 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm)
mm->hmm = NULL;
spin_unlock(&mm->page_table_lock);
error:
+ mmdrop(hmm->mm);
kfree(hmm);
return NULL;
}
@@ -121,6 +124,7 @@ static void hmm_free(struct kref *kref)
mm->hmm = NULL;
spin_unlock(&mm->page_table_lock);

+ mmdrop(hmm->mm);
mmu_notifier_call_srcu(&hmm->rcu, hmm_free_rcu);
}

@@ -129,24 +133,6 @@ static inline void hmm_put(struct hmm *hmm)
kref_put(&hmm->kref, hmm_free);
}

-void hmm_mm_destroy(struct mm_struct *mm)
-{
- struct hmm *hmm;
-
- spin_lock(&mm->page_table_lock);
- hmm = mm_get_hmm(mm);
- mm->hmm = NULL;
- if (hmm) {
- hmm->mm = NULL;
- hmm->dead = true;
- spin_unlock(&mm->page_table_lock);
- hmm_put(hmm);
- return;
- }
-
- spin_unlock(&mm->page_table_lock);
-}
-
static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
--
2.20.1
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