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Subject[PATCH] vmalloc: respect the GFP_NOIO and GFP_NOFS flags
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;
}

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