tree 52d85afaa21a97aabdd10e2ae4cef8c0d1b09c6c
parent b90cb1053190353cc30f0fef0ef1f378ccc063c5
author Fabio M. De Francesco <fmdefrancesco@gmail.com> 1660077062 +0200
committer Andrew Morton <akpm@linux-foundation.org> 1662958504 -0700

hfsplus: unmap the page in the "fail_page" label

Patch series "hfsplus: 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
kmap’s 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/hfsplus is safe everywhere, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in fs/hfsplus.  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 (1/4).

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


This patch (of 4):

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/20220809203105.26183-1-fmdefrancesco@gmail.com
Link: https://lkml.kernel.org/r/20220809203105.26183-2-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>