From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
The rules to this function state that mmap_sem must
be acquired by the caller:
- for write if used in f_op->mmap() (by far the most common case)
- for read if used from vma_op->fault()(with VM_MIXEDMAP)
The only exception is:
mmap_vmcore()
remap_vmalloc_range_partial()
mmap_vmcore()
But there is no concurrency here, thus mmap_sem is not held.
After auditing the kernel, the following drivers use the fault
path and correctly set VM_MIXEDMAP):
.fault = etnaviv_gem_fault
.fault = udl_gem_fault
tegra_bo_fault()
As such, drop the reader trylock BUG_ON() for the common case.
This avoids having file_operations know about mmranges, as
mmap_sem is held during, mmap() for example.
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
---
mm/memory.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 5adcdc7dee80..7c69674cd9da 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1773,7 +1773,6 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
if (!page_count(page))
return -EINVAL;
if (!(vma->vm_flags & VM_MIXEDMAP)) {
- BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
BUG_ON(vma->vm_flags & VM_PFNMAP);
vma->vm_flags |= VM_MIXEDMAP;
}
--
2.13.6
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