The __vmalloc function has a parameter gfp_mask with the allocation flags,
however it doesn't fully respect the GFP_NOIO and GFP_NOFS flags. The
pages are allocated with the specified gfp flags, but the pagetables are
always allocated with GFP_KERNEL. This allocation can cause unexpected
recursion into the filesystem or I/O subsystem.

It is not practical to extend page table allocation routines with gfp
flags because it would require modification of architecture-specific code
in all architecturs. However, the process can temporarily request that all
allocations are done with GFP_NOFS or GFP_NOIO with with the functions
memalloc_nofs_save and memalloc_noio_save.

This patch makes the vmalloc code use memalloc_nofs_save or
memalloc_noio_save if the supplied gfp flags do not contain __GFP_FS or
__GFP_IO. It fixes some possible deadlocks in drivers/mtd/ubi/io.c,
fs/gfs2/, fs/btrfs/free-space-tree.c, fs/ubifs/,
fs/nfs/blocklayout/extent_tree.c where __vmalloc is used with the GFP_NOFS
flag.

The patch also simplifies code in dm-bufio.c, dm-ioctl.c and fs/xfs/kmem.c
by removing explicit calls to memalloc_nofs_save and memalloc_noio_save
before the call to __vmalloc.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-bufio.c |   24 +-----------------------
 drivers/md/dm-ioctl.c |    6 +-----
 fs/xfs/kmem.c         |   14 --------------
 mm/util.c             |    6 +++---
 mm/vmalloc.c          |   18 +++++++++++++++++-
 5 files changed, 22 insertions(+), 46 deletions(-)

Index: linux-2.6/mm/vmalloc.c
===================================================================

--- linux-2.6.orig/mm/vmalloc.c
+++ linux-2.6/mm/vmalloc.c

@@ -31,6 +31,7 @@
 #include <linux/compiler.h>
 #include <linux/llist.h>
 #include <linux/bitops.h>
+#include <linux/sched/mm.h>
 
 #include <linux/uaccess.h>
 #include <asm/tlbflush.h>

@@ -1670,6 +1671,8 @@ static void *__vmalloc_area_node(struct
 	unsigned int nr_pages, array_size, i;
 	const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
 	const gfp_t alloc_mask = gfp_mask | __GFP_HIGHMEM | __GFP_NOWARN;
+	unsigned noio_flag;
+	int r;
 
 	nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
 	array_size = (nr_pages * sizeof(struct page *));

@@ -1712,8 +1715,21 @@ static void *__vmalloc_area_node(struct
 			cond_resched();
 	}
 
-	if (map_vm_area(area, prot, pages))
+	if (unlikely(!(gfp_mask & __GFP_IO)))
+		noio_flag = memalloc_noio_save();
+	else if (unlikely(!(gfp_mask & __GFP_FS)))
+		noio_flag = memalloc_nofs_save();
+
+	r = map_vm_area(area, prot, pages);
+
+	if (unlikely(!(gfp_mask & __GFP_IO)))
+		memalloc_noio_restore(noio_flag);
+	else if (unlikely(!(gfp_mask & __GFP_FS)))
+		memalloc_nofs_restore(noio_flag);
+
+	if (unlikely(r))
 		goto fail;
+
 	return area->addr;
 
 fail:

Index: linux-2.6/mm/util.c
===================================================================

--- linux-2.6.orig/mm/util.c
+++ linux-2.6/mm/util.c

@@ -351,10 +351,10 @@ void *kvmalloc_node(size_t size, gfp_t f
 	void *ret;
 
 	/*
-	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
-	 * so the given set of flags has to be compatible.
+	 * vmalloc uses blocking allocations for some internal allocations
+	 * (e.g page tables) so the given set of flags has to be compatible.
 	 */
-	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
+	WARN_ON_ONCE(!gfpflags_allow_blocking(flags));

 
 	/*
 	 * We want to attempt a large physically contiguous block first because
Index: linux-2.6/drivers/md/dm-bufio.c
===================================================================

--- linux-2.6.orig/drivers/md/dm-bufio.c
+++ linux-2.6/drivers/md/dm-bufio.c

@@ -386,9 +386,6 @@ static void __cache_size_refresh(void)
 static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
 			       enum data_mode *data_mode)
 {
-	unsigned noio_flag;
-	void *ptr;
-
 	if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) {
 		*data_mode = DATA_MODE_SLAB;
 		return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask);

@@ -402,26 +399,7 @@ static void *alloc_buffer_data(struct dm
 	}
 
 	*data_mode = DATA_MODE_VMALLOC;
-
-	/*
-	 * __vmalloc allocates the data pages and auxiliary structures with
-	 * gfp_flags that were specified, but pagetables are always allocated
-	 * with GFP_KERNEL, no matter what was specified as gfp_mask.
-	 *
-	 * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that
-	 * all allocations done by this process (including pagetables) are done
-	 * as if GFP_NOIO was specified.
-	 */
-
-	if (gfp_mask & __GFP_NORETRY)
-		noio_flag = memalloc_noio_save();
-
-	ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
-
-	if (gfp_mask & __GFP_NORETRY)
-		memalloc_noio_restore(noio_flag);
-
-	return ptr;
+	return __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);

 }
 
 /*
Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================

--- linux-2.6.orig/drivers/md/dm-ioctl.c
+++ linux-2.6/drivers/md/dm-ioctl.c

@@ -1691,7 +1691,6 @@ static int copy_params(struct dm_ioctl _
 	struct dm_ioctl *dmi;
 	int secure_data;
 	const size_t minimum_data_size = offsetof(struct dm_ioctl, data);
-	unsigned noio_flag;
 
 	if (copy_from_user(param_kernel, user, minimum_data_size))
 		return -EFAULT;

@@ -1714,10 +1713,7 @@ static int copy_params(struct dm_ioctl _
 	 * suspended and the ioctl is needed to resume it.
 	 * Use kmalloc() rather than vmalloc() when we can.
 	 */
-	dmi = NULL;
-	noio_flag = memalloc_noio_save();
-	dmi = kvmalloc(param_kernel->data_size, GFP_KERNEL | __GFP_HIGH);
-	memalloc_noio_restore(noio_flag);
+	dmi = kvmalloc(param_kernel->data_size, GFP_NOIO | __GFP_HIGH);

 
 	if (!dmi) {
 		if (secure_data && clear_user(user, param_kernel->data_size))
Index: linux-2.6/fs/xfs/kmem.c
===================================================================

--- linux-2.6.orig/fs/xfs/kmem.c
+++ linux-2.6/fs/xfs/kmem.c

@@ -48,7 +48,6 @@ kmem_alloc(size_t size, xfs_km_flags_t f
 void *
 kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
 {
-	unsigned nofs_flag = 0;
 	void	*ptr;
 	gfp_t	lflags;
 

@@ -56,22 +55,9 @@ kmem_zalloc_large(size_t size, xfs_km_fl
 	if (ptr)
 		return ptr;
 
-	/*
-	 * __vmalloc() will allocate data pages and auxillary structures (e.g.
-	 * pagetables) with GFP_KERNEL, yet we may be under GFP_NOFS context
-	 * here. Hence we need to tell memory reclaim that we are in such a
-	 * context via PF_MEMALLOC_NOFS to prevent memory reclaim re-entering
-	 * the filesystem here and potentially deadlocking.
-	 */
-	if (flags & KM_NOFS)
-		nofs_flag = memalloc_nofs_save();
-
 	lflags = kmem_flags_convert(flags);
 	ptr = __vmalloc(size, lflags | __GFP_ZERO, PAGE_KERNEL);
 
-	if (flags & KM_NOFS)
-		memalloc_nofs_restore(nofs_flag);
-
 	return ptr;
 }