[v7,1/9] mm: Allow the [page|pfn]_mkwrite callbacks to drop the mmap_sem

Commit Message

Thomas Hellström (VMware) June 17, 2019, 8:17 p.m. UTC

From: Thomas Hellstrom <[e-mail]>

Driver fault callbacks are allowed to drop the mmap_sem when expecting
long hardware waits to avoid blocking other mm users. Allow the mkwrite
callbacks to do the same by returning early on VM_FAULT_RETRY.

In particular we want to be able to drop the mmap_sem when waiting for
a reservation object lock on a GPU buffer object. These locks may be
held while waiting for the GPU.

Cc: Andrew Morton <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Huang Ying <[e-mail]>
Cc: Souptick Joarder <[e-mail]>
Cc: "Jérôme Glisse" <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]

Signed-off-by: Thomas Hellstrom <[e-mail]>
Reviewed-by: Ralph Campbell <[e-mail]>
---
 mm/memory.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Patch

diff --git a/mm/memory.c b/mm/memory.c
index ddf20bd0c317..168f546af1ad 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2238,7 +2238,7 @@  static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
 	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
 	/* Restore original flags so that caller is not surprised */
 	vmf->flags = old_flags;
-	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
 		return ret;
 	if (unlikely(!(ret & VM_FAULT_LOCKED))) {
 		lock_page(page);
@@ -2515,7 +2515,7 @@  static vm_fault_t wp_pfn_shared(struct vm_fault *vmf)
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		vmf->flags |= FAULT_FLAG_MKWRITE;
 		ret = vma->vm_ops->pfn_mkwrite(vmf);
-		if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
+		if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))
 			return ret;
 		return finish_mkwrite_fault(vmf);
 	}
@@ -2536,7 +2536,8 @@  static vm_fault_t wp_page_shared(struct vm_fault *vmf)
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		tmp = do_page_mkwrite(vmf);
 		if (unlikely(!tmp || (tmp &
-				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
+				       VM_FAULT_RETRY)))) {
 			put_page(vmf->page);
 			return tmp;
 		}
@@ -3601,7 +3602,8 @@  static vm_fault_t do_shared_fault(struct vm_fault *vmf)
 		unlock_page(vmf->page);
 		tmp = do_page_mkwrite(vmf);
 		if (unlikely(!tmp ||
-				(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+				(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
+					VM_FAULT_RETRY)))) {
 			put_page(vmf->page);
 			return tmp;
 		}