alloc_tag: allocate percpu counters for module tags dynamically

alloc_tag: allocate percpu counters for module tags dynamically

When a module gets unloaded it checks whether any of its tags are still in
use and if so, we keep the memory containing module's allocation tags
alive until all tags are unused.  However percpu counters referenced by
the tags are freed by free_module().  This will lead to UAF if the memory
allocated by a module is accessed after module was unloaded.

To fix this we allocate percpu counters for module allocation tags
dynamically and we keep it alive for tags which are still in use after
module unloading.  This also removes the requirement of a larger
PERCPU_MODULE_RESERVE when memory allocation profiling is enabled because
percpu memory for counters does not need to be reserved anymore.

Link: https://lkml.kernel.org/r/20250517000739.5930-1-surenb@google.com
Fixes: 0db6f8d7820a ("alloc_tag: load module tags into separate contiguous memory")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: David Wang <00107082@163.com>
Closes: https://lore.kernel.org/all/20250516131246.6244-1-00107082@163.com/
Tested-by: David Wang <00107082@163.com>
Cc: Christoph Lameter (Ampere) <cl@gentwo.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>