Commit 5e31275c authored by Suren Baghdasaryan's avatar Suren Baghdasaryan Committed by Andrew Morton

mm: add per-VMA lock and helper functions to control it

Introduce per-VMA locking.  The lock implementation relies on a per-vma
and per-mm sequence counters to note exclusive locking:

  - read lock - (implemented by vma_start_read) requires the vma
    (vm_lock_seq) and mm (mm_lock_seq) sequence counters to differ.
    If they match then there must be a vma exclusive lock held somewhere.
  - read unlock - (implemented by vma_end_read) is a trivial vma->lock
    unlock.
  - write lock - (vma_start_write) requires the mmap_lock to be held
    exclusively and the current mm counter is assigned to the vma counter.
    This will allow multiple vmas to be locked under a single mmap_lock
    write lock (e.g. during vma merging). The vma counter is modified
    under exclusive vma lock.
  - write unlock - (vma_end_write_all) is a batch release of all vma
    locks held. It doesn't pair with a specific vma_start_write! It is
    done before exclusive mmap_lock is released by incrementing mm
    sequence counter (mm_lock_seq).
  - write downgrade - if the mmap_lock is downgraded to the read lock, all
    vma write locks are released as well (effectivelly same as write
    unlock).

Link: https://lkml.kernel.org/r/20230227173632.3292573-13-surenb@google.comSigned-off-by: default avatarSuren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 438b6e12
......@@ -624,6 +624,87 @@ struct vm_operations_struct {
unsigned long addr);
};
#ifdef CONFIG_PER_VMA_LOCK
static inline void vma_init_lock(struct vm_area_struct *vma)
{
init_rwsem(&vma->lock);
vma->vm_lock_seq = -1;
}
/*
* Try to read-lock a vma. The function is allowed to occasionally yield false
* locked result to avoid performance overhead, in which case we fall back to
* using mmap_lock. The function should never yield false unlocked result.
*/
static inline bool vma_start_read(struct vm_area_struct *vma)
{
/* Check before locking. A race might cause false locked result. */
if (vma->vm_lock_seq == READ_ONCE(vma->vm_mm->mm_lock_seq))
return false;
if (unlikely(down_read_trylock(&vma->lock) == 0))
return false;
/*
* Overflow might produce false locked result.
* False unlocked result is impossible because we modify and check
* vma->vm_lock_seq under vma->lock protection and mm->mm_lock_seq
* modification invalidates all existing locks.
*/
if (unlikely(vma->vm_lock_seq == READ_ONCE(vma->vm_mm->mm_lock_seq))) {
up_read(&vma->lock);
return false;
}
return true;
}
static inline void vma_end_read(struct vm_area_struct *vma)
{
rcu_read_lock(); /* keeps vma alive till the end of up_read */
up_read(&vma->lock);
rcu_read_unlock();
}
static inline void vma_start_write(struct vm_area_struct *vma)
{
int mm_lock_seq;
mmap_assert_write_locked(vma->vm_mm);
/*
* current task is holding mmap_write_lock, both vma->vm_lock_seq and
* mm->mm_lock_seq can't be concurrently modified.
*/
mm_lock_seq = READ_ONCE(vma->vm_mm->mm_lock_seq);
if (vma->vm_lock_seq == mm_lock_seq)
return;
down_write(&vma->lock);
vma->vm_lock_seq = mm_lock_seq;
up_write(&vma->lock);
}
static inline void vma_assert_write_locked(struct vm_area_struct *vma)
{
mmap_assert_write_locked(vma->vm_mm);
/*
* current task is holding mmap_write_lock, both vma->vm_lock_seq and
* mm->mm_lock_seq can't be concurrently modified.
*/
VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
}
#else /* CONFIG_PER_VMA_LOCK */
static inline void vma_init_lock(struct vm_area_struct *vma) {}
static inline bool vma_start_read(struct vm_area_struct *vma)
{ return false; }
static inline void vma_end_read(struct vm_area_struct *vma) {}
static inline void vma_start_write(struct vm_area_struct *vma) {}
static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
#endif /* CONFIG_PER_VMA_LOCK */
static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
{
static const struct vm_operations_struct dummy_vm_ops = {};
......@@ -632,6 +713,7 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
vma->vm_mm = mm;
vma->vm_ops = &dummy_vm_ops;
INIT_LIST_HEAD(&vma->anon_vma_chain);
vma_init_lock(vma);
}
/* Use when VMA is not part of the VMA tree and needs no locking */
......
......@@ -503,6 +503,11 @@ struct vm_area_struct {
vm_flags_t __private __vm_flags;
};
#ifdef CONFIG_PER_VMA_LOCK
int vm_lock_seq;
struct rw_semaphore lock;
#endif
/*
* For areas with an address space and backing store,
* linkage into the address_space->i_mmap interval tree.
......@@ -639,6 +644,9 @@ struct mm_struct {
* init_mm.mmlist, and are protected
* by mmlist_lock
*/
#ifdef CONFIG_PER_VMA_LOCK
int mm_lock_seq;
#endif
unsigned long hiwater_rss; /* High-watermark of RSS usage */
......
......@@ -72,6 +72,17 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm)
VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
}
#ifdef CONFIG_PER_VMA_LOCK
static inline void vma_end_write_all(struct mm_struct *mm)
{
mmap_assert_write_locked(mm);
/* No races during update due to exclusive mmap_lock being held */
WRITE_ONCE(mm->mm_lock_seq, mm->mm_lock_seq + 1);
}
#else
static inline void vma_end_write_all(struct mm_struct *mm) {}
#endif
static inline void mmap_init_lock(struct mm_struct *mm)
{
init_rwsem(&mm->mmap_lock);
......@@ -114,12 +125,14 @@ static inline bool mmap_write_trylock(struct mm_struct *mm)
static inline void mmap_write_unlock(struct mm_struct *mm)
{
__mmap_lock_trace_released(mm, true);
vma_end_write_all(mm);
up_write(&mm->mmap_lock);
}
static inline void mmap_write_downgrade(struct mm_struct *mm)
{
__mmap_lock_trace_acquire_returned(mm, false, true);
vma_end_write_all(mm);
downgrade_write(&mm->mmap_lock);
}
......
......@@ -474,6 +474,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
*/
data_race(memcpy(new, orig, sizeof(*new)));
INIT_LIST_HEAD(&new->anon_vma_chain);
vma_init_lock(new);
dup_anon_vma_name(orig, new);
}
return new;
......@@ -1208,6 +1209,9 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
seqcount_init(&mm->write_protect_seq);
mmap_init_lock(mm);
INIT_LIST_HEAD(&mm->mmlist);
#ifdef CONFIG_PER_VMA_LOCK
mm->mm_lock_seq = 0;
#endif
mm_pgtables_bytes_init(mm);
mm->map_count = 0;
mm->locked_vm = 0;
......
......@@ -37,6 +37,9 @@ struct mm_struct init_mm = {
.page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
.arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
#ifdef CONFIG_PER_VMA_LOCK
.mm_lock_seq = 0,
#endif
.user_ns = &init_user_ns,
.cpu_bitmap = CPU_BITS_NONE,
#ifdef CONFIG_IOMMU_SVA
......
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