From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D9A2F326D51; Sat, 18 Apr 2026 07:54:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776498867; cv=none; b=jDbde1Kal2l7cl2DQZ3vv0N2nGDF4YLFdwLyGcPfDkmhMOPqvXSmam9pOIJV2qKf5DH7CEyE3IAM0jJ9dv98gfpf3t6SCxx0/qVS33LF4pRHrM9N+ZYxE+UxAhqUIDMSKws/aiRYNkC7gf/8G0NRbbSO8BmhvIANnMfVN9cKHEU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776498867; c=relaxed/simple; bh=wFvCoqWhYgGGcuqJtrlS88sFlh8e2qjgtOLd9JjBhHY=; h=Date:To:From:Subject:Message-Id; b=ov5KLVPY7OzCwFyfdBzGjmvUi34irvDKt6YVotkTxo4S6MyHht25JUJNU01cPml1N1fsRs0cjiUXdjECLMZzD/50MQYe7QWwWqFPm4vqToiimsZPydH7Vj3O1GvaQ9LZjX6ALRMl6Z1z7u47ArrGK+Z4+fBXZwXTKSwyha4Uz8Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ZgmZuzrW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ZgmZuzrW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 911FBC19424; Sat, 18 Apr 2026 07:54:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1776498867; bh=wFvCoqWhYgGGcuqJtrlS88sFlh8e2qjgtOLd9JjBhHY=; h=Date:To:From:Subject:From; b=ZgmZuzrWy4+BVO6MsE4TyCMq3ePZWwOiRP/MtLJIlKAW+S+2gq8DT0bTkzMofw7U4 7sG1XfXrif7pxmck8m73NTWEWq5pbwaMaY+d4C69qU+9a0Rzo3WYW2MZRGrr6MbfqB s394u8yh6H41J5R/rG0abYTfe3JbHrokK0nu4uUA= Date: Sat, 18 Apr 2026 00:54:21 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,sj@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race.patch removed from -mm tree Message-Id: <20260418075426.911FBC19424@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/damon/core: fix damos_walk() vs kdamond_fn() exit race has been removed from the -mm tree. Its filename was mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: SeongJae Park Subject: mm/damon/core: fix damos_walk() vs kdamond_fn() exit race Date: Fri, 27 Mar 2026 16:33:15 -0700 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]. Link: https://lore.kernel.org/20260327233319.3528-3-sj@kernel.org Link: https://lore.kernel.org/20260325141956.87144-1-sj@kernel.org [1] Fixes: bf0eaba0ff9c ("mm/damon/core: implement damos_walk()") Signed-off-by: SeongJae Park Cc: # 6.14.x Signed-off-by: Andrew Morton --- include/linux/damon.h | 1 + mm/damon/core.c | 21 ++++++++++++++------- 2 files changed, 15 insertions(+), 7 deletions(-) --- a/include/linux/damon.h~mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race +++ a/include/linux/damon.h @@ -822,6 +822,7 @@ struct damon_ctx { struct mutex call_controls_lock; struct damos_walk_control *walk_control; + bool walk_control_obsolete; struct mutex walk_control_lock; /* --- a/mm/damon/core.c~mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race +++ a/mm/damon/core.c @@ -1637,6 +1637,10 @@ int damon_call(struct damon_ctx *ctx, st * passed at least one &damos->apply_interval_us, kdamond marks the request as * completed so that damos_walk() can wakeup and return. * + * Note that this function should be called only after damon_start() with the + * @ctx has succeeded. Otherwise, this function could fall into an indefinite + * wait. + * * Return: 0 on success, negative error code otherwise. */ int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control) @@ -1644,19 +1648,16 @@ int damos_walk(struct damon_ctx *ctx, st init_completion(&control->completion); control->canceled = false; mutex_lock(&ctx->walk_control_lock); + if (ctx->walk_control_obsolete) { + mutex_unlock(&ctx->walk_control_lock); + return -ECANCELED; + } if (ctx->walk_control) { mutex_unlock(&ctx->walk_control_lock); return -EBUSY; } ctx->walk_control = control; mutex_unlock(&ctx->walk_control_lock); - if (!damon_is_running(ctx)) { - mutex_lock(&ctx->walk_control_lock); - if (ctx->walk_control == control) - ctx->walk_control = NULL; - mutex_unlock(&ctx->walk_control_lock); - return -EINVAL; - } wait_for_completion(&control->completion); if (control->canceled) return -ECANCELED; @@ -2932,6 +2933,9 @@ static int kdamond_fn(void *data) mutex_lock(&ctx->call_controls_lock); ctx->call_controls_obsolete = false; mutex_unlock(&ctx->call_controls_lock); + mutex_lock(&ctx->walk_control_lock); + ctx->walk_control_obsolete = false; + mutex_unlock(&ctx->walk_control_lock); complete(&ctx->kdamond_started); kdamond_init_ctx(ctx); @@ -3046,6 +3050,9 @@ done: ctx->call_controls_obsolete = true; mutex_unlock(&ctx->call_controls_lock); kdamond_call(ctx, true); + mutex_lock(&ctx->walk_control_lock); + ctx->walk_control_obsolete = true; + mutex_unlock(&ctx->walk_control_lock); damos_walk_cancel(ctx); pr_debug("kdamond (%d) finishes\n", current->pid); _ Patches currently in -mm which might be from sj@kernel.org are mm-damon-core-disallow-time-quota-setting-zero-esz.patch mm-damon-core-disallow-non-power-of-two-min_region_sz-on-damon_start.patch