Btrfs: use memalloc_nofs and kvzalloc() for free space tree bitmaps

First, instead of open-coding the vmalloc() fallback, use the new
kvzalloc() helper. Second, use memalloc_nofs_{save,restore}() instead of
GFP_NOFS, as vmalloc() uses some GFP_KERNEL allocations internally which
could lead to deadlocks.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index c7397b05511912e246299b1866a9d69865b98fdf..a5e34de06c2fe593e7578d59a27614f73a57ea1a 100644 (file)
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -17,7 +17,7 @@
  */
 
 #include <linux/kernel.h>
-#include <linux/vmalloc.h>
+#include <linux/sched/mm.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "locking.h"
@@ -153,21 +153,21 @@ static inline u32 free_space_bitmap_size(u64 size, u32 sectorsize)
 
 static u8 *alloc_bitmap(u32 bitmap_size)
 {
-       void *mem;
+       u8 *ret;
+       unsigned int nofs_flag;
 
        /*
-        * The allocation size varies, observed numbers were < 4K up to 16K.
-        * Using vmalloc unconditionally would be too heavy, we'll try
-        * contiguous allocations first.
+        * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse
+        * into the filesystem as the free space bitmap can be modified in the
+        * critical section of a transaction commit.
+        *
+        * TODO: push the memalloc_nofs_{save,restore}() to the caller where we
+        * know that recursion is unsafe.
         */
-       if  (bitmap_size <= PAGE_SIZE)
-               return kzalloc(bitmap_size, GFP_NOFS);
-
-       mem = kzalloc(bitmap_size, GFP_NOFS | __GFP_NOWARN);
-       if (mem)
-               return mem;
-
-       return __vmalloc(bitmap_size, GFP_NOFS | __GFP_ZERO, PAGE_KERNEL);
+       nofs_flag = memalloc_nofs_save();
+       ret = kvzalloc(bitmap_size, GFP_KERNEL);
+       memalloc_nofs_restore(nofs_flag);
+       return ret;
 }
 
 int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,