alloc_tag: skip percpu counter allocation when profiling is disabled

Patch series "alloc_tag: fix a leak and a deadlock around
shutdown_mem_profiling()", v2.

Two fixes for issues reported by sashiko:

  1. percpu counter leak on modules loaded after profiling is disabled.
  2. AB-BA deadlock between module load and /proc/allocinfo readers.


This patch (of 2):

After shutdown_mem_profiling() clears mem_profiling_support,
needs_section_mem() returns false, so later modules have their codetag
section placed as regular data and never enter the alloc_tag maple tree. 
codetag_load_module() still called load_module(), which allocated a percpu
counter for every tag; release_module_tags() could not find these modules
on unload, so the counters leaked.

Return -EOPNOTSUPP from load_module() when profiling is off:
codetag_module_init() drops the module's cmod, no counters are allocated
and the module loads without its tags.  codetag_unload_module() now always
calls free_section_mem(), since a module whose module_load() returned
-EOPNOTSUPP is not in the idr but may still hold a reserved section.

Link: https://lore.kernel.org/20260817062726.106511-1-hao.ge@linux.dev
Link: https://lore.kernel.org/20260817062726.106511-2-hao.ge@linux.dev
Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Signed-off-by: Hao Ge <hao.ge@linux.dev>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/lib/codetag.c b/lib/codetag.c
index a9cda4c962a3..a0b600720afc 100644
--- a/lib/codetag.c
+++ b/lib/codetag.c
@@ -240,7 +240,9 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
 
 	if (err < 0) {
 		kfree(cmod);
-		return err;
+		/* -EOPNOTSUPP means we can load the module without its tag. */
+		if (err != -EOPNOTSUPP)
+			return err;
 	}
 
 	return 0;
@@ -388,7 +390,11 @@ void codetag_unload_module(struct module *mod)
 			++cttype->content_id;
 		}
 		up_write(&cttype->mod_lock);
-		if (found && cttype->desc.free_section_mem)
+		/*
+		 * A module whose module_load() returned -EOPNOTSUPP is not
+		 * in the idr but may still hold reserved section memory.
+		 */
+		if (cttype->desc.free_section_mem)
 			cttype->desc.free_section_mem(mod, true);
 	}
 	mutex_unlock(&codetag_lock);