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mm/hmm: Hold on to the mmget for the lifetime of the range 

Range functions like hmm_range_snapshot() and hmm_range_fault() call
find_vma, which requires hodling the mmget() and the mmap_sem for the mm.

Make this simpler for the callers by holding the mmget() inside the range
for the lifetime of the range. Other functions that accept a range should
only be called if the range is registered.

This has the side effect of directly preventing hmm_release() from
happening while a range is registered. That means range->dead cannot be
false during the lifetime of the range, so remove dead and
hmm_mirror_mm_is_alive() entirely.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>
This commit is contained in:
Jason Gunthorpe 2019-05-23 11:08:28 -03:00
parent 157816f377
commit 47f245985a
2 changed files with 11 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
include/linux/hmm.h
View File

@ -82,7 +82,6 @@
* @mirrors_sem: read/write semaphore protecting the mirrors list
* @wq: wait queue for user waiting on a range invalidation
* @notifiers: count of active mmu notifiers
* @dead: is the mm dead ?
*/
struct hmm {
struct mm_struct *mm;
@ -95,7 +94,6 @@ struct hmm {
wait_queue_head_t wq;
struct rcu_head rcu;
long notifiers;
bool dead;
};
/*
@ -459,30 +457,6 @@ struct hmm_mirror {
int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm);
void hmm_mirror_unregister(struct hmm_mirror *mirror);
/*
* hmm_mirror_mm_is_alive() - test if mm is still alive
* @mirror: the HMM mm mirror for which we want to lock the mmap_sem
* Return: false if the mm is dead, true otherwise
*
* This is an optimization, it will not always accurately return false if the
* mm is dead; i.e., there can be false negatives (process is being killed but
* HMM is not yet informed of that). It is only intended to be used to optimize
* out cases where the driver is about to do something time consuming and it
* would be better to skip it if the mm is dead.
*/
static inline bool hmm_mirror_mm_is_alive(struct hmm_mirror *mirror)
{
struct mm_struct *mm;
if (!mirror || !mirror->hmm)
return false;
mm = READ_ONCE(mirror->hmm->mm);
if (mirror->hmm->dead || !mm)
return false;
return true;
}
/*
* Please see Documentation/vm/hmm.rst for how to use the range API.
*/

32
mm/hmm.c
View File

@ -67,7 +67,6 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm)
mutex_init(&hmm->lock);
kref_init(&hmm->kref);
hmm->notifiers = 0;
hmm->dead = false;
hmm->mm = mm;
hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
@ -120,21 +119,16 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);
struct hmm_mirror *mirror;
struct hmm_range *range;
/* Bail out if hmm is in the process of being freed */
if (!kref_get_unless_zero(&hmm->kref))
return;
/* Report this HMM as dying. */
hmm->dead = true;
/* Wake-up everyone waiting on any range. */
mutex_lock(&hmm->lock);
list_for_each_entry(range, &hmm->ranges, list)
range->valid = false;
wake_up_all(&hmm->wq);
mutex_unlock(&hmm->lock);
/*
* Since hmm_range_register() holds the mmget() lock hmm_release() is
* prevented as long as a range exists.
*/
WARN_ON(!list_empty_careful(&hmm->ranges));
down_write(&hmm->mirrors_sem);
mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
@ -903,8 +897,8 @@ int hmm_range_register(struct hmm_range *range,
range->start = start;
range->end = end;
/* Check if hmm_mm_destroy() was call. */
if (hmm->mm == NULL || hmm->dead)
/* Prevent hmm_release() from running while the range is valid */
if (!mmget_not_zero(hmm->mm))
return -EFAULT;
/* Initialize range to track CPU page table updates. */
@ -942,11 +936,12 @@ void hmm_range_unregister(struct hmm_range *range)
return;
mutex_lock(&hmm->lock);
list_del(&range->list);
list_del_init(&range->list);
mutex_unlock(&hmm->lock);
/* Drop reference taken by hmm_range_register() */
range->valid = false;
mmput(hmm->mm);
hmm_put(hmm);
range->hmm = NULL;
}
@ -974,10 +969,7 @@ long hmm_range_snapshot(struct hmm_range *range)
struct vm_area_struct *vma;
struct mm_walk mm_walk;
/* Check if hmm_mm_destroy() was call. */
if (hmm->mm == NULL || hmm->dead)
return -EFAULT;
lockdep_assert_held(&hmm->mm->mmap_sem);
do {
/* If range is no longer valid force retry. */
if (!range->valid)
@ -1072,9 +1064,7 @@ long hmm_range_fault(struct hmm_range *range, bool block)
struct mm_walk mm_walk;
int ret;
/* Check if hmm_mm_destroy() was call. */
if (hmm->mm == NULL || hmm->dead)
return -EFAULT;
lockdep_assert_held(&hmm->mm->mmap_sem);
do {
/* If range is no longer valid force retry. */