linuxkpi: GFP_KERNEL equals M_NOWAIT now

... instead of `M_WAITOK`.

[Why]
The reason is that in some places in the DRM drivers (in particular, the
framebuffer management code), kmalloc() is called from a non-sleepable
context, such as after a call to mtx_lock(8) with an MTX_DEF mutex.

If `GFP_KERNEL` is defined as `M_WAITOK`, we hit an assertion from
witness(4).

[How]
The definition of `GFP_KERNEL` is changed to `M_NOWAIT`. This means that
callers should verify the return value of kmalloc(). Fortunately, this
is always the case in Linux.

Reviewed by:	bz, emaste, manu
Approved by:	manu
Differential Revision:  https://reviews.freebsd.org/D42054

sys/compat/linuxkpi/common/include/linux/gfp.h

@@ -64,7 +64,7 @@
 
 #define	GFP_NOWAIT	M_NOWAIT
 #define	GFP_ATOMIC	(M_NOWAIT | M_USE_RESERVE)
-#define	GFP_KERNEL	M_WAITOK
+#define	GFP_KERNEL	M_NOWAIT
 #define	GFP_USER	M_WAITOK
 #define	GFP_HIGHUSER	M_WAITOK
 #define	GFP_HIGHUSER_MOVABLE	M_WAITOK

sys/compat/linuxkpi/common/include/linux/slab.h

@@ -47,12 +47,12 @@ MALLOC_DECLARE(M_KMALLOC);
 #define	kzalloc(size, flags)		kmalloc(size, (flags) | __GFP_ZERO)
 #define	kzalloc_node(size, flags, node)	kmalloc_node(size, (flags) | __GFP_ZERO, node)
 #define	kfree_const(ptr)		kfree(ptr)
-#define	vzalloc(size)			__vmalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_ZERO, 0)
+#define	vzalloc(size)			__vmalloc(size, M_WAITOK | __GFP_NOWARN | __GFP_ZERO, 0)
 #define	vfree(arg)			kfree(arg)
 #define	kvfree(arg)			kfree(arg)
-#define	vmalloc_node(size, node)	__vmalloc_node(size, GFP_KERNEL, node)
-#define	vmalloc_user(size)		__vmalloc(size, GFP_KERNEL | __GFP_ZERO, 0)
-#define	vmalloc(size)			__vmalloc(size, GFP_KERNEL, 0)
+#define	vmalloc_node(size, node)	__vmalloc_node(size, M_WAITOK, node)
+#define	vmalloc_user(size)		__vmalloc(size, M_WAITOK | __GFP_ZERO, 0)
+#define	vmalloc(size)			__vmalloc(size, M_WAITOK, 0)
 #define	__kmalloc(...)			kmalloc(__VA_ARGS__)
 
 /*

sys/compat/linuxkpi/common/src/linux_compat.c

@@ -574,7 +574,7 @@ linux_file_alloc(void)
 {
 	struct linux_file *filp;
 
-	filp = kzalloc(sizeof(*filp), GFP_KERNEL);
+	filp = kzalloc(sizeof(*filp), M_WAITOK);
 
 	/* set initial refcount */
 	filp->f_count = 1;
@@ -1412,6 +1412,9 @@ linux_file_mmap_single(struct file *fp, const struct file_operations *fop,
 		return (EINVAL);
 
 	vmap = kzalloc(sizeof(*vmap), GFP_KERNEL);
+	if (vmap == NULL)
+		return (ENOMEM);
+
 	vmap->vm_start = 0;
 	vmap->vm_end = size;
 	vmap->vm_pgoff = *offset / PAGE_SIZE;
@@ -1941,7 +1944,7 @@ vmmap_add(void *addr, unsigned long size)
 {
 	struct vmmap *vmmap;
 
-	vmmap = kmalloc(sizeof(*vmmap), GFP_KERNEL);
+	vmmap = kmalloc(sizeof(*vmmap), M_WAITOK);
 	mtx_lock(&vmmaplock);
 	vmmap->vm_size = size;
 	vmmap->vm_addr = addr;

sys/compat/linuxkpi/common/src/linux_interrupt.c

@@ -135,6 +135,9 @@ lkpi_request_irq(struct device *xdev, unsigned int irq,
 		    GFP_KERNEL | __GFP_ZERO);
 	else
 		irqe = kzalloc(sizeof(*irqe), GFP_KERNEL);
+	if (irqe == NULL)
+		return (-ENOMEM);
+
 	irqe->dev = dev;
 	irqe->res = res;
 	irqe->arg = arg;

sys/compat/linuxkpi/common/src/linux_pci.c

@@ -305,7 +305,7 @@ lkpifill_pci_dev(device_t dev, struct pci_dev *pdev)
 	pdev->subsystem_device = pci_get_subdevice(dev);
 	pdev->class = pci_get_class(dev);
 	pdev->revision = pci_get_revid(dev);
-	pdev->path_name = kasprintf(GFP_KERNEL, "%04d:%02d:%02d.%d",
+	pdev->path_name = kasprintf(M_WAITOK, "%04d:%02d:%02d.%d",
 	    pci_get_domain(dev), pci_get_bus(dev), pci_get_slot(dev),
 	    pci_get_function(dev));
 	pdev->bus = malloc(sizeof(*pdev->bus), M_DEVBUF, M_WAITOK | M_ZERO);
@@ -1469,7 +1469,7 @@ linux_dma_pool_create(char *name, struct device *dev, size_t size,
 
 	priv = dev->dma_priv;
 
-	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
+	pool = kzalloc(sizeof(*pool), M_WAITOK);
 	pool->pool_device = dev;
 	pool->pool_entry_size = size;
 

sys/compat/linuxkpi/common/src/linux_shmemfs.c

@@ -48,8 +48,15 @@ linux_shmem_read_mapping_page_gfp(vm_object_t obj, int pindex, gfp_t gfp)
 	struct page *page;
 	int rv;
 
-	if ((gfp & GFP_NOWAIT) != 0)
-		panic("GFP_NOWAIT is unimplemented");
+	/*
+	 * Historically, GFP_KERNEL was the equivalent of M_WAITOK. But it was
+	 * changed to a synonym of M_NOWAIT to allow allocations in
+	 * non-sleepable code.
+	 *
+	 * However, there was an assertion here to make sure that `gfp` was
+	 * never set to GFP_NOWAIT/M_NOWAIT. Do we need a specific handling of
+	 * M_NOWAIT here?
+	 */
 
 	VM_OBJECT_WLOCK(obj);
 	rv = vm_page_grab_valid(&page, obj, pindex, VM_ALLOC_NORMAL |