nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint

Patch series "nilfs2: fix null-ptr-deref bugs on block tracepoints".

This series fixes null pointer dereference bugs that occur when using

nilfs2 and two block-related tracepoints.

This patch (of 2):

It has been reported that when using "block:block_touch_buffer"

tracepoint, touch_buffer() called from __nilfs_get_folio_block() causes a

NULL pointer dereference, or a general protection fault when KASAN is

enabled.

This happens because since the tracepoint was added in touch_buffer(), it

references the dev_t member bh->b_bdev->bd_dev regardless of whether the

buffer head has a pointer to a block_device structure. In the current

implementation, the block_device structure is set after the function

returns to the caller.

Here, touch_buffer() is used to mark the folio/page that owns the buffer

head as accessed, but the common search helper for folio/page used by the

caller function was optimized to mark the folio/page as accessed when it

was reimplemented a long time ago, eliminating the need to call

touch_buffer() here in the first place.

So this solves the issue by eliminating the touch_buffer() call itself.