[openib-general] Re: [PATCH] process locked in D state.

[Michael S. Tsirkin]

Quoting r. Roland Dreier <rolandd at cisco.com>:
> Subject: Re: [PATCH] process locked in D state.
> 
> Something like this should work...

Note that there's a window when close() has returned but
vm_locked isnt updated yet.
Actually, a process that doesnt close memory regions before
closing the device will leak (virtual) memory anyway.

The only interesting case is of the process exiting, in which case mm is
NULL.

So I propose to kill all this code.

Signed-off-by: Michael S. Tsirkin <mst at mellanox.co.il>

Index: core/uverbs_mem.c
===================================================================
--- core/uverbs_mem.c	(revision 2724)
+++ core/uverbs_mem.c	(working copy)
@@ -180,40 +180,7 @@ static void ib_umem_account(void *work_p
 
 void ib_umem_release(struct ib_device *dev, struct ib_umem *umem)
 {
-	struct mm_struct *mm;
-
+	/* A well-behaved application will close regions before
+	 * closing the file. Thus we dont have to update mm->locked_vm here. */
 	__ib_umem_release(dev, umem, 1);
-
-	mm = get_task_mm(current);
-	if (mm) {
-		/*
-		 * We may be called with the mm's mmap_sem already
-		 * held.  This can happen when a userspace munmap() is
-		 * the call that drops the last reference to our file
-		 * and calls our release method.  If there are memory
-		 * regions to destroy, we'll end up here and not be
-		 * able to take the mmap_sem.
-		 *
-		 * To handle this, we try to grab the mmap_sem, and if
-		 * we can't get it immediately, we defer the
-		 * accounting to the system workqueue.
-		 */
-		if (down_write_trylock(&mm->mmap_sem)) {
-			mm->locked_vm -= PAGE_ALIGN(umem->length + umem->offset) >> PAGE_SHIFT;
-			up_write(&mm->mmap_sem);
-			mmput(mm);
-		} else {
-			struct ib_umem_account_work *work;
-
-			work = kmalloc(sizeof *work, GFP_KERNEL);
-			if (!work)
-				return;
-
-			INIT_WORK(&work->work, ib_umem_account, work);
-			work->mm   = mm;
-			work->diff = PAGE_ALIGN(umem->length + umem->offset) >> PAGE_SHIFT;
-
-			schedule_work(&work->work);
-		}
-	}
 }

-- 
MST