CVE-2026-46008

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/core: fix damos_walk() vs kdamond_fn() exit race

When kdamond_fn() main loop is finished, the function cancels remaining

damos_walk() request and unset the damon_ctx->kdamond so that API callers

and API functions themselves can show the context is terminated.

damos_walk() adds the caller's request to the queue first. After that, it

shows if the kdamond of the damon_ctx is still running (damon_ctx->kdamond

is set). Only if the kdamond is running, damos_walk() starts waiting for

the kdamond's handling of the newly added request.

The damos_walk() requests registration and damon_ctx->kdamond unset are

protected by different mutexes, though. Hence, damos_walk() could race

with damon_ctx->kdamond unset, and result in deadlocks.

For example, let's suppose kdamond successfully finished the damow_walk()

request cancelling. Right after that, damos_walk() is called for the

context. It registers the new request, and shows the context is still

running, because damon_ctx->kdamond unset is not yet done. Hence the

damos_walk() caller starts waiting for the handling of the request.

However, the kdamond is already on the termination steps, so it never

handles the new request. As a result, the damos_walk() caller thread

infinitely waits.

Fix this by introducing another damon_ctx field, namely

walk_control_obsolete. It is protected by the

damon_ctx->walk_control_lock, which protects damos_walk() request

registration. Initialize (unset) it in kdamond_fn() before letting

damon_start() returns and set it just before the cancelling of the

remaining damos_walk() request is executed. damos_walk() reads the

obsolete field under the lock and avoids adding a new request.

After this change, only requests that are guaranteed to be handled or

cancelled are registered. Hence the after-registration DAMON context

termination check is no longer needed. Remove it together.

The issue is found by sashiko [1].