[PATCH 15/48] staging: etnaviv: etnaviv_gem_fault: reduce struct_mutex exposure

[Lucas Stach]

From: Russell King <rmk+ker...@arm.linux.org.uk>

Reduce the exposure of struct_mutex to an absolute minimum.  We only
need to take this lock over the call to etnaviv_gem_get_pages() as
vm_insert_page() already does a properly synchronised update of the
PTE (using the pte table lock.)

Reducing the code covered by this lock allows for more parallel
execution in SMP environments.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/staging/etnaviv/etnaviv_gem.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/etnaviv/etnaviv_gem.c 
b/drivers/staging/etnaviv/etnaviv_gem.c
index 69360c899b78..522e5a6c3612 100644
--- a/drivers/staging/etnaviv/etnaviv_gem.c
+++ b/drivers/staging/etnaviv/etnaviv_gem.c
@@ -221,8 +221,10 @@ int etnaviv_gem_fault(struct vm_area_struct *vma, struct 
vm_fault *vmf)
        pgoff_t pgoff;
        int ret;

-       /* Make sure we don't parallel update on a fault, nor move or remove
-        * something from beneath our feet
+       /*
+        * Make sure we don't parallel update on a fault, nor move or remove
+        * something from beneath our feet.  Note that vm_insert_page() is
+        * specifically coded to take care of this, so we don't have to.
         */
        ret = mutex_lock_interruptible(&dev->struct_mutex);
        if (ret)
@@ -230,9 +232,11 @@ int etnaviv_gem_fault(struct vm_area_struct *vma, struct 
vm_fault *vmf)

        /* make sure we have pages attached now */
        pages = etnaviv_gem_get_pages(to_etnaviv_bo(obj));
+       mutex_unlock(&dev->struct_mutex);
+
        if (IS_ERR(pages)) {
                ret = PTR_ERR(pages);
-               goto out_unlock;
+               goto out;
        }

        /* We don't use vmf->pgoff since that has the fake offset: */
@@ -246,8 +250,6 @@ int etnaviv_gem_fault(struct vm_area_struct *vma, struct 
vm_fault *vmf)

        ret = vm_insert_page(vma, (unsigned long)vmf->virtual_address, page);

-out_unlock:
-       mutex_unlock(&dev->struct_mutex);
 out:
        switch (ret) {
        case -EAGAIN:
-- 
2.5.1