From: Jann Horn <jannh@xxxxxxxxxx> Subject: mm/gup_benchmark: take the mmap lock around GUP To be safe against concurrent changes to the VMA tree, we must take the mmap lock around GUP operations (excluding the GUP-fast family of operations, which will take the mmap lock by themselves if necessary). This code is only for testing, and it's only reachable by root through debugfs, so this doesn't really have any impact; however, if we want to add lockdep asserts into the GUP path, we need to have clean locking here. Link: https://lkml.kernel.org/r/CAG48ez3SG6ngZLtasxJ6LABpOnqCz5-QHqb0B4k44TQ8F9n6+w@xxxxxxxxxxxxxx Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> Acked-by: Michel Lespinasse <walken@xxxxxxxxxx> Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup_benchmark.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) --- a/mm/gup_benchmark.c~mm-gup_benchmark-take-the-mmap-lock-around-gup +++ a/mm/gup_benchmark.c @@ -72,6 +72,8 @@ static int __gup_benchmark_ioctl(unsigne int nr; struct page **pages; int ret = 0; + bool needs_mmap_lock = + cmd != GUP_FAST_BENCHMARK && cmd != PIN_FAST_BENCHMARK; if (gup->size > ULONG_MAX) return -EINVAL; @@ -81,6 +83,11 @@ static int __gup_benchmark_ioctl(unsigne if (!pages) return -ENOMEM; + if (needs_mmap_lock && mmap_read_lock_killable(current->mm)) { + ret = -EINTR; + goto free_pages; + } + i = 0; nr = gup->nr_pages_per_call; start_time = ktime_get(); @@ -120,9 +127,8 @@ static int __gup_benchmark_ioctl(unsigne pages + i, NULL); break; default: - kvfree(pages); ret = -EINVAL; - goto out; + goto unlock; } if (nr <= 0) @@ -150,8 +156,11 @@ static int __gup_benchmark_ioctl(unsigne end_time = ktime_get(); gup->put_delta_usec = ktime_us_delta(end_time, start_time); +unlock: + if (needs_mmap_lock) + mmap_read_unlock(current->mm); +free_pages: kvfree(pages); -out: return ret; } _
