dax: Fix stack overflow when mounting fsdax pmem device

When mounting fsdax pmem device, commit 6180bb446ab6 ("dax: fix
detection of dax support for non-persistent memory block devices")
introduces the stack overflow [1][2]. Here is the call path for
mounting ext4 file system:
  ext4_fill_super
    bdev_dax_supported
      __bdev_dax_supported
        dax_supported
          generic_fsdax_supported
            __generic_fsdax_supported
              bdev_dax_supported

The call path leads to the infinite calling loop, so we cannot
call bdev_dax_supported() in __generic_fsdax_supported(). The sanity
checking of the variable 'dax_dev' is moved prior to the two
bdev_dax_pgoff() checks [3][4].

[1] https://lore.kernel.org/linux-nvdimm/1420999447.1004543.1600055488770[email protected]/
[2] https://lore.kernel.org/linux-nvdimm/alpine.LRH.2.02.2009141131220[email protected]/
[3] https://lore.kernel.org/linux-nvdimm/CA+RJvhxBHriCuJhm-D8NvJRe3h2MLM+ZMFgjeJjrRPerMRLvdg@mail.gmail.com/
[4] https://lore.kernel.org/linux-nvdimm/20200903160608[email protected]/

Fixes: 6180bb446ab6 ("dax: fix detection of dax support for non-persistent memory block devices")
Reported-by: Yi Zhang <[email protected]>
Reported-by: Mikulas Patocka <[email protected]>
Signed-off-by: Adrian Huang <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Tested-by: Ritesh Harjani <[email protected]>
Cc: Coly Li <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: John Pittman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dan Williams <[email protected]>

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index b6284c5cae0a8f7eec2391c2556eac9cddd60ee7..e84070b5546362a7a05da0fa4784cc6f46a6476f 100644 (file)
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -85,6 +85,12 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
                return false;
        }
 
+       if (!dax_dev) {
+               pr_debug("%s: error: dax unsupported by block device\n",
+                               bdevname(bdev, buf));
+               return false;
+       }
+
        err = bdev_dax_pgoff(bdev, start, PAGE_SIZE, &pgoff);
        if (err) {
                pr_info("%s: error: unaligned partition for dax\n",
@@ -100,12 +106,6 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
                return false;
        }
 
-       if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
-               pr_debug("%s: error: dax unsupported by block device\n",
-                               bdevname(bdev, buf));
-               return false;
-       }
-
        id = dax_read_lock();
        len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
        len2 = dax_direct_access(dax_dev, pgoff_end, 1, &end_kaddr, &end_pfn);