mm/gup_test: keep longterm pin state per file

The pin longterm test currently stores its data globally, shared among
multiple concurrent users of the interface (multiple open file descriptors
-> multiple "struct file"'s).  That makes the gup_test interface
problematic to use concurrently: two users, such as concurrent selftest
runs, can interfere with the same longterm pin state.

While this has not been observed as a problem so far in practice, let's
just handle it cleanly.  There could be a way to trigger selftest failures
by e.g., running the cow.c and gup_longerm.c selftests concurrently, but
we usually run them sequentially.  Let's add a "Fixes" tag to be safe, but
not need to CC stable.

Link: https://lore.kernel.org/20260810-gup_test_data-v1-1-fb1d41be5bb4@kernel.org
Fixes: c77369b437f9 ("mm/gup_test: start/stop/read functionality for PIN LONGTERM test")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reported-by: yunhui cui <cuiyunhui@bytedance.com>
Closes: https://lore.kernel.org/r/20260608025043.88087-1-cuiyunhui@bytedance.com
Tested-by: Yunhui Cui <cuiyunhui@bytedance.com>
Tested-by: Lance Yang <lance.yang@linux.dev>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions