[PATCH 4/6] fpga/dlf/afu: drop mmap_sem now that locked_vm is atomic

[Daniel Jordan]

With locked_vm now an atomic, there is no need to take mmap_sem as
writer.  Delete and refactor accordingly.

Signed-off-by: Daniel Jordan <daniel.m.jor...@oracle.com>
Cc: Alan Tull <at...@kernel.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Christoph Lameter <c...@linux.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Moritz Fischer <m...@kernel.org>
Cc: Wu Hao <hao...@intel.com>
Cc: <linux...@kvack.org>
Cc: <linux-f...@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
---
 drivers/fpga/dfl-afu-dma-region.c | 40 ++++++++++++-------------------
 1 file changed, 15 insertions(+), 25 deletions(-)

diff --git a/drivers/fpga/dfl-afu-dma-region.c 
b/drivers/fpga/dfl-afu-dma-region.c
index 08132fd9b6b7..81e3e3a71758 100644
--- a/drivers/fpga/dfl-afu-dma-region.c
+++ b/drivers/fpga/dfl-afu-dma-region.c
@@ -35,46 +35,36 @@ void afu_dma_region_init(struct dfl_feature_platform_data 
*pdata)
  * afu_dma_adjust_locked_vm - adjust locked memory
  * @dev: port device
  * @npages: number of pages
- * @incr: increase or decrease locked memory
  *
  * Increase or decrease the locked memory size with npages input.
  *
  * Return 0 on success.
  * Return -ENOMEM if locked memory size is over the limit and no CAP_IPC_LOCK.
  */
-static int afu_dma_adjust_locked_vm(struct device *dev, long npages, bool incr)
+static int afu_dma_adjust_locked_vm(struct device *dev, long pages)
 {
-       unsigned long locked, lock_limit;
+       unsigned long lock_limit;
        s64 locked_vm;
        int ret = 0;
 
        /* the task is exiting. */
-       if (!current->mm)
+       if (!current->mm || !pages)
                return 0;
 
-       down_write(&current->mm->mmap_sem);
-
-       locked_vm = atomic64_read(&current->mm->locked_vm);
-       if (incr) {
-               locked = locked_vm + npages;
+       locked_vm = atomic64_add_return(pages, &current->mm->locked_vm);
+       WARN_ON_ONCE(locked_vm < 0);
+       if (pages > 0 && !capable(CAP_IPC_LOCK)) {
                lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-
-               if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+               if (locked_vm > lock_limit) {
                        ret = -ENOMEM;
-               else
-                       atomic64_add(npages, &current->mm->locked_vm);
-       } else {
-               if (WARN_ON_ONCE(npages > locked_vm))
-                       npages = locked_vm;
-               atomic64_sub(npages, &current->mm->locked_vm);
+                       atomic64_sub(pages, &current->mm->locked_vm);
+               }
        }
 
        dev_dbg(dev, "[%d] RLIMIT_MEMLOCK %c%ld %lld/%lu%s\n", current->pid,
-               incr ? '+' : '-', npages << PAGE_SHIFT,
-               (s64)atomic64_read(&current->mm->locked_vm) << PAGE_SHIFT,
-               rlimit(RLIMIT_MEMLOCK), ret ? "- exceeded" : "");
-
-       up_write(&current->mm->mmap_sem);
+               (pages > 0) ? '+' : '-', pages << PAGE_SHIFT,
+               locked_vm << PAGE_SHIFT, rlimit(RLIMIT_MEMLOCK),
+               ret ? "- exceeded" : "");
 
        return ret;
 }
@@ -94,7 +84,7 @@ static int afu_dma_pin_pages(struct dfl_feature_platform_data 
*pdata,
        struct device *dev = &pdata->dev->dev;
        int ret, pinned;
 
-       ret = afu_dma_adjust_locked_vm(dev, npages, true);
+       ret = afu_dma_adjust_locked_vm(dev, npages);
        if (ret)
                return ret;
 
@@ -123,7 +113,7 @@ static int afu_dma_pin_pages(struct 
dfl_feature_platform_data *pdata,
 free_pages:
        kfree(region->pages);
 unlock_vm:
-       afu_dma_adjust_locked_vm(dev, npages, false);
+       afu_dma_adjust_locked_vm(dev, -npages);
        return ret;
 }
 
@@ -143,7 +133,7 @@ static void afu_dma_unpin_pages(struct 
dfl_feature_platform_data *pdata,
 
        put_all_pages(region->pages, npages);
        kfree(region->pages);
-       afu_dma_adjust_locked_vm(dev, npages, false);
+       afu_dma_adjust_locked_vm(dev, -npages);
 
        dev_dbg(dev, "%ld pages unpinned\n", npages);
 }
-- 
2.21.0