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Subject[PATCH 2/2] mm, util: account_locked_vm() does not hold mmap_lock
Date
Since mm->locked_vm is already an atomic counter, account_locked_vm()
does not need to hold mmap_lock.

Signed-off-by: Pengfei Li <fly@kernel.page>
---
drivers/vfio/vfio_iommu_type1.c | 8 ++------
mm/util.c | 15 +++------------
2 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 78013be07fe7..53818fce78a6 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -376,12 +376,8 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
if (!mm)
return -ESRCH; /* process exited */

- ret = mmap_write_lock_killable(mm);
- if (!ret) {
- ret = __account_locked_vm(mm, abs(npage), npage > 0, dma->task,
- dma->lock_cap);
- mmap_write_unlock(mm);
- }
+ ret = __account_locked_vm(mm, abs(npage), npage > 0,
+ dma->task, dma->lock_cap);

if (async)
mmput(mm);
diff --git a/mm/util.c b/mm/util.c
index 473add0dc275..320fdd537aea 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -424,8 +424,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
* @task: task used to check RLIMIT_MEMLOCK
* @bypass_rlim: %true if checking RLIMIT_MEMLOCK should be skipped
*
- * Assumes @task and @mm are valid (i.e. at least one reference on each), and
- * that mmap_lock is held as writer.
+ * Assumes @task and @mm are valid (i.e. at least one reference on each).
*
* Return:
* * 0 on success
@@ -437,8 +436,6 @@ int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
unsigned long locked_vm, limit;
int ret = 0;

- mmap_assert_write_locked(mm);
-
locked_vm = atomic64_read(&mm->locked_vm);
if (inc) {
if (!bypass_rlim) {
@@ -476,17 +473,11 @@ EXPORT_SYMBOL_GPL(__account_locked_vm);
*/
int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc)
{
- int ret;
-
if (pages == 0 || !mm)
return 0;

- mmap_write_lock(mm);
- ret = __account_locked_vm(mm, pages, inc, current,
- capable(CAP_IPC_LOCK));
- mmap_write_unlock(mm);
-
- return ret;
+ return __account_locked_vm(mm, pages, inc,
+ current, capable(CAP_IPC_LOCK));
}
EXPORT_SYMBOL_GPL(account_locked_vm);

--
2.26.2
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