hfs: unmap the page in the "fail_page" label

Patch series "hfs: Replace kmap() with kmap_local_page()".

kmap() is being deprecated in favor of kmap_local_page().

There are two main problems with kmap(): (1) It comes with an overhead as
mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmaps pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts). 
It is faster than kmap() in kernels with HIGHMEM enabled.  Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and still valid.

Since its use in fs/hfs is safe everywhere, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in fs/hfs.  Where
possible, use the suited standard helpers (memzero_page(), memcpy_page())
instead of open coding kmap_local_page() plus memset() or memcpy().

Fix a bug due to a page being not unmapped if the code jumps to the
"fail_page" label (1/3).

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.


This patch (of 3):

Several paths within hfs_btree_open() jump to the "fail_page" label where
put_page() is called while the page is still mapped.

Call kunmap() to unmap the page soon before put_page().

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Fabio M. De Francesco <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Viacheslav Dubeyko <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Chaitanya Kulkarni <[email protected]>
Cc: Christian Brauner (Microsoft) <[email protected]>
Cc: Damien Le Moal <[email protected]>
Cc: Matthew Wilcox <[email protected]>]
Cc: Jeff Layton <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Martin K. Petersen <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions