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Subject[PATCH v3 hmm 04/11] misc/sgi-gru: use mmu_notifier_get/put for struct gru_mm_struct
Date
From: Jason Gunthorpe <jgg@mellanox.com>

GRU is already using almost the same algorithm as get/put, it even
helpfully has a 10 year old comment to make this algorithm common, which
is finally happening.

There are a few differences and fixes from this conversion:
- GRU used rcu not srcu to read the hlist
- Unclear how the locking worked to prevent gru_register_mmu_notifier()
from running concurrently with gru_drop_mmu_notifier() - this version is
safe
- GRU had a release function which only set a variable without any locking
that skiped the synchronize_srcu during unregister which looks racey,
but this makes it reliable via the integrated call_srcu().
- It is unclear if the mmap_sem is actually held when
__mmu_notifier_register() was called, lockdep will now warn if this is
wrong

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
drivers/misc/sgi-gru/grufile.c | 1 +
drivers/misc/sgi-gru/grutables.h | 2 -
drivers/misc/sgi-gru/grutlbpurge.c | 84 +++++++++---------------------
3 files changed, 25 insertions(+), 62 deletions(-)

diff --git a/drivers/misc/sgi-gru/grufile.c b/drivers/misc/sgi-gru/grufile.c
index a2a142ae087bfa..9d042310214ff9 100644
--- a/drivers/misc/sgi-gru/grufile.c
+++ b/drivers/misc/sgi-gru/grufile.c
@@ -573,6 +573,7 @@ static void __exit gru_exit(void)
gru_free_tables();
misc_deregister(&gru_miscdev);
gru_proc_exit();
+ mmu_notifier_synchronize();
}

static const struct file_operations gru_fops = {
diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h
index 438191c220570c..a7e44b2eb413f6 100644
--- a/drivers/misc/sgi-gru/grutables.h
+++ b/drivers/misc/sgi-gru/grutables.h
@@ -307,10 +307,8 @@ struct gru_mm_tracker { /* pack to reduce size */

struct gru_mm_struct {
struct mmu_notifier ms_notifier;
- atomic_t ms_refcnt;
spinlock_t ms_asid_lock; /* protects ASID assignment */
atomic_t ms_range_active;/* num range_invals active */
- char ms_released;
wait_queue_head_t ms_wait_queue;
DECLARE_BITMAP(ms_asidmap, GRU_MAX_GRUS);
struct gru_mm_tracker ms_asids[GRU_MAX_GRUS];
diff --git a/drivers/misc/sgi-gru/grutlbpurge.c b/drivers/misc/sgi-gru/grutlbpurge.c
index 59ba0adf23cee4..10921cd2608dfa 100644
--- a/drivers/misc/sgi-gru/grutlbpurge.c
+++ b/drivers/misc/sgi-gru/grutlbpurge.c
@@ -235,83 +235,47 @@ static void gru_invalidate_range_end(struct mmu_notifier *mn,
gms, range->start, range->end);
}

-static void gru_release(struct mmu_notifier *mn, struct mm_struct *mm)
+static struct mmu_notifier *gru_alloc_notifier(struct mm_struct *mm)
{
- struct gru_mm_struct *gms = container_of(mn, struct gru_mm_struct,
- ms_notifier);
+ struct gru_mm_struct *gms;
+
+ gms = kzalloc(sizeof(*gms), GFP_KERNEL);
+ if (!gms)
+ return ERR_PTR(-ENOMEM);
+ STAT(gms_alloc);
+ spin_lock_init(&gms->ms_asid_lock);
+ init_waitqueue_head(&gms->ms_wait_queue);

- gms->ms_released = 1;
- gru_dbg(grudev, "gms %p\n", gms);
+ return &gms->ms_notifier;
}

+static void gru_free_notifier(struct mmu_notifier *mn)
+{
+ kfree(container_of(mn, struct gru_mm_struct, ms_notifier));
+ STAT(gms_free);
+}

static const struct mmu_notifier_ops gru_mmuops = {
.invalidate_range_start = gru_invalidate_range_start,
.invalidate_range_end = gru_invalidate_range_end,
- .release = gru_release,
+ .alloc_notifier = gru_alloc_notifier,
+ .free_notifier = gru_free_notifier,
};

-/* Move this to the basic mmu_notifier file. But for now... */
-static struct mmu_notifier *mmu_find_ops(struct mm_struct *mm,
- const struct mmu_notifier_ops *ops)
-{
- struct mmu_notifier *mn, *gru_mn = NULL;
-
- if (mm->mmu_notifier_mm) {
- rcu_read_lock();
- hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list,
- hlist)
- if (mn->ops == ops) {
- gru_mn = mn;
- break;
- }
- rcu_read_unlock();
- }
- return gru_mn;
-}
-
struct gru_mm_struct *gru_register_mmu_notifier(void)
{
- struct gru_mm_struct *gms;
struct mmu_notifier *mn;
- int err;
-
- mn = mmu_find_ops(current->mm, &gru_mmuops);
- if (mn) {
- gms = container_of(mn, struct gru_mm_struct, ms_notifier);
- atomic_inc(&gms->ms_refcnt);
- } else {
- gms = kzalloc(sizeof(*gms), GFP_KERNEL);
- if (!gms)
- return ERR_PTR(-ENOMEM);
- STAT(gms_alloc);
- spin_lock_init(&gms->ms_asid_lock);
- gms->ms_notifier.ops = &gru_mmuops;
- atomic_set(&gms->ms_refcnt, 1);
- init_waitqueue_head(&gms->ms_wait_queue);
- err = __mmu_notifier_register(&gms->ms_notifier, current->mm);
- if (err)
- goto error;
- }
- if (gms)
- gru_dbg(grudev, "gms %p, refcnt %d\n", gms,
- atomic_read(&gms->ms_refcnt));
- return gms;
-error:
- kfree(gms);
- return ERR_PTR(err);
+
+ mn = mmu_notifier_get_locked(&gru_mmuops, current->mm);
+ if (IS_ERR(mn))
+ return ERR_CAST(mn);
+
+ return container_of(mn, struct gru_mm_struct, ms_notifier);
}

void gru_drop_mmu_notifier(struct gru_mm_struct *gms)
{
- gru_dbg(grudev, "gms %p, refcnt %d, released %d\n", gms,
- atomic_read(&gms->ms_refcnt), gms->ms_released);
- if (atomic_dec_return(&gms->ms_refcnt) == 0) {
- if (!gms->ms_released)
- mmu_notifier_unregister(&gms->ms_notifier, current->mm);
- kfree(gms);
- STAT(gms_free);
- }
+ mmu_notifier_put(&gms->ms_notifier);
}

/*
--
2.22.0
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