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Subject[PATCH 2/6] mic/scif: do not use mmap_sem
Date
The driver uses mmap_sem for both pinned_vm accounting and
get_user_pages(). By using gup_fast() and letting the mm handle
the lock if needed, we can no longer rely on the semaphore and
simplify the whole thing.

Cc: sudeep.dutt@intel.com
Cc: ashutosh.dixit@intel.com
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
drivers/misc/mic/scif/scif_rma.c | 36 +++++++++++-------------------------
1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/drivers/misc/mic/scif/scif_rma.c b/drivers/misc/mic/scif/scif_rma.c
index 2448368f181e..263b8ad507ea 100644
--- a/drivers/misc/mic/scif/scif_rma.c
+++ b/drivers/misc/mic/scif/scif_rma.c
@@ -272,21 +272,12 @@ static inline void __scif_release_mm(struct mm_struct *mm)

static inline int
__scif_dec_pinned_vm_lock(struct mm_struct *mm,
- int nr_pages, bool try_lock)
+ int nr_pages)
{
if (!mm || !nr_pages || !scif_ulimit_check)
return 0;
- if (try_lock) {
- if (!down_write_trylock(&mm->mmap_sem)) {
- dev_err(scif_info.mdev.this_device,
- "%s %d err\n", __func__, __LINE__);
- return -1;
- }
- } else {
- down_write(&mm->mmap_sem);
- }
+
atomic64_sub(nr_pages, &mm->pinned_vm);
- up_write(&mm->mmap_sem);
return 0;
}

@@ -298,16 +289,16 @@ static inline int __scif_check_inc_pinned_vm(struct mm_struct *mm,
if (!mm || !nr_pages || !scif_ulimit_check)
return 0;

- locked = nr_pages;
- locked += atomic64_read(&mm->pinned_vm);
lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+ locked = atomic64_add_return(nr_pages, &mm->pinned_vm);
+
if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
+ atomic64_sub(nr_pages, &mm->pinned_vm);
dev_err(scif_info.mdev.this_device,
"locked(%lu) > lock_limit(%lu)\n",
locked, lock_limit);
return -ENOMEM;
}
- atomic64_set(&mm->pinned_vm, locked);
return 0;
}

@@ -326,7 +317,7 @@ int scif_destroy_window(struct scif_endpt *ep, struct scif_window *window)

might_sleep();
if (!window->temp && window->mm) {
- __scif_dec_pinned_vm_lock(window->mm, window->nr_pages, 0);
+ __scif_dec_pinned_vm_lock(window->mm, window->nr_pages);
__scif_release_mm(window->mm);
window->mm = NULL;
}
@@ -737,7 +728,7 @@ int scif_unregister_window(struct scif_window *window)
ep->rma_info.dma_chan);
} else {
if (!__scif_dec_pinned_vm_lock(window->mm,
- window->nr_pages, 1)) {
+ window->nr_pages)) {
__scif_release_mm(window->mm);
window->mm = NULL;
}
@@ -1385,28 +1376,23 @@ int __scif_pin_pages(void *addr, size_t len, int *out_prot,
prot |= SCIF_PROT_WRITE;
retry:
mm = current->mm;
- down_write(&mm->mmap_sem);
if (ulimit) {
err = __scif_check_inc_pinned_vm(mm, nr_pages);
if (err) {
- up_write(&mm->mmap_sem);
pinned_pages->nr_pages = 0;
goto error_unmap;
}
}

- pinned_pages->nr_pages = get_user_pages(
+ pinned_pages->nr_pages = get_user_pages_fast(
(u64)addr,
nr_pages,
(prot & SCIF_PROT_WRITE) ? FOLL_WRITE : 0,
- pinned_pages->pages,
- NULL);
- up_write(&mm->mmap_sem);
+ pinned_pages->pages);
if (nr_pages != pinned_pages->nr_pages) {
if (try_upgrade) {
if (ulimit)
- __scif_dec_pinned_vm_lock(mm,
- nr_pages, 0);
+ __scif_dec_pinned_vm_lock(mm, nr_pages);
/* Roll back any pinned pages */
for (i = 0; i < pinned_pages->nr_pages; i++) {
if (pinned_pages->pages[i])
@@ -1433,7 +1419,7 @@ int __scif_pin_pages(void *addr, size_t len, int *out_prot,
return err;
dec_pinned:
if (ulimit)
- __scif_dec_pinned_vm_lock(mm, nr_pages, 0);
+ __scif_dec_pinned_vm_lock(mm, nr_pages);
/* Something went wrong! Rollback */
error_unmap:
pinned_pages->nr_pages = nr_pages;
--
2.16.4
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