Revert "linuxkpi: `GFP_KERNEL` equals `M_NOWAIT` now"

This change seems to break some drivers such as the mlx5*(4) drivers.

As kib@ says:
> According to the 'official' Linux kernel documentation, the GFP_KERNEL
> flag implies sleepable context.

It was introduced while working on the new vt(4)/DRM integration [1].
During this work, doing sleepable allocations broke vt(4) and the DRM
drivers. However, I made further improvements and some locking-related
fixed to the new integration without revisiting the need for it.

After more testing, the improvements to the integration mentionned above
seems to make the change to `GFP_KERNEL` unneeded now. I can thus
revert it to restore expectations of other drivers.

This reverts commit 14dcd40983.

[1] https://github.com/freebsd/drm-kmod/pull/243

Reviewed by:	kib
Approved by:	kib
Differential Revision:	https://reviews.freebsd.org/D42962

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

@@ -63,7 +63,7 @@
 
 #define	GFP_NOWAIT	M_NOWAIT
 #define	GFP_ATOMIC	(M_NOWAIT | M_USE_RESERVE)
-#define	GFP_KERNEL	M_NOWAIT
+#define	GFP_KERNEL	M_WAITOK
 #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, M_WAITOK | __GFP_NOWARN | __GFP_ZERO, 0)
+#define	vzalloc(size)			__vmalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_ZERO, 0)
 #define	vfree(arg)			kfree(arg)
 #define	kvfree(arg)			kfree(arg)
-#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	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	__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), M_WAITOK);
+	filp = kzalloc(sizeof(*filp), GFP_KERNEL);
 
 	/* set initial refcount */
 	filp->f_count = 1;
@@ -1412,9 +1412,6 @@ 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;
@@ -1944,7 +1941,7 @@ vmmap_add(void *addr, unsigned long size)
 {
 	struct vmmap *vmmap;
 
-	vmmap = kmalloc(sizeof(*vmmap), M_WAITOK);
+	vmmap = kmalloc(sizeof(*vmmap), GFP_KERNEL);
 	mtx_lock(&vmmaplock);
 	vmmap->vm_size = size;
 	vmmap->vm_addr = addr;

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

@@ -135,9 +135,6 @@ 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

@@ -304,7 +304,7 @@ 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(M_WAITOK, "%04d:%02d:%02d.%d",
+	pdev->path_name = kasprintf(GFP_KERNEL, "%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);
@@ -1468,7 +1468,7 @@ linux_dma_pool_create(char *name, struct device *dev, size_t size,
 
 	priv = dev->dma_priv;
 
-	pool = kzalloc(sizeof(*pool), M_WAITOK);
+	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
 	pool->pool_device = dev;
 	pool->pool_entry_size = size;
 

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

@@ -47,15 +47,8 @@ linux_shmem_read_mapping_page_gfp(vm_object_t obj, int pindex, gfp_t gfp)
 	struct page *page;
 	int rv;
 
-	/*
-	 * 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?
-	 */
+	if ((gfp & GFP_NOWAIT) != 0)
+		panic("GFP_NOWAIT is unimplemented");
 
 	VM_OBJECT_WLOCK(obj);
 	rv = vm_page_grab_valid(&page, obj, pindex, VM_ALLOC_NORMAL |