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 59F4235FF58 for ; Sun, 29 Mar 2026 16:22:01 +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=1774801322; cv=none; b=RZtDuislSMBE/KGvOBG6FwWDOJ/RQCQuSj85TdpGuBiCFRnubAUOIvyAr86p/VvINo1iaJhmYeL7gSF8cj8aMRfCVM/sCh55uMQ9P+Fdhx2eWWnXTx+nK9aisrnKvhXxa+5mfFbiaHtc+nXYZl81T0SiaYAy+/7O+C+LUE8V56g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774801322; c=relaxed/simple; bh=CPPzlWUbMbTOc/U6leI3v1BPV04vETobDPjoiG6G/5o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XYNmaEM+k8WCgn2mmxHpMXjWs6TQSV5/riNq5JgsRdwd8j2Orb+z8j9qUnhivURc5QcIgHLYfrGWNQ3lnm0xNc8BSzx1Rifskj+J/iCOLOona7LXO7RVsgM+la/muASCN5g/+32vG6l57daaSEgF4E91GpzcS0xU0GCFk6wscko= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=prJWhsIi; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="prJWhsIi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 917E1C116C6; Sun, 29 Mar 2026 16:22:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774801321; bh=CPPzlWUbMbTOc/U6leI3v1BPV04vETobDPjoiG6G/5o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=prJWhsIigzwQUCBUfkbJsFxZeBk3POrjuTk1PAWeXhSxnXLqzmIp0MjgsbDhg90Vy HgmPedOTOu6XmVkARLXsIxUDR7z5OcSoCM86Cq+lYptKDDVYjqcsnZWbaqlvbtDdaf Y9eL/tcg0fuuId2xBnjPOhengNtU0vbbQElBdKnb/mueE6hjkXGDRqaWasv++uiASi SxxQfFuWufgLt8Sodue4qyzYdJSlAfpJdRoOBkJ6qeQN8oc+9e/E9qy84h7LQTGLpP SOGtqC7nHBiebWb++c/D0KOSxe3X7jutRmAj9IBJNko4liT8PlnpeFcuM2DQo7HsJW 7xfnwj+lGdznA== From: SeongJae Park To: stable@vger.kernel.org Cc: SeongJae Park , Andrew Morton Subject: [PATCH 6.19.y] mm/damon/core: avoid use of half-online-committed context Date: Sun, 29 Mar 2026 09:21:59 -0700 Message-ID: <20260329162159.56306-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026032924-italicize-animate-f383@gregkh> References: <2026032924-italicize-animate-f383@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit One major usage of damon_call() is online DAMON parameters update. It is done by calling damon_commit_ctx() inside the damon_call() callback function. damon_commit_ctx() can fail for two reasons: 1) invalid parameters and 2) internal memory allocation failures. In case of failures, the damon_ctx that attempted to be updated (commit destination) can be partially updated (or, corrupted from a perspective), and therefore shouldn't be used anymore. The function only ensures the damon_ctx object can safely deallocated using damon_destroy_ctx(). The API callers are, however, calling damon_commit_ctx() only after asserting the parameters are valid, to avoid damon_commit_ctx() fails due to invalid input parameters. But it can still theoretically fail if the internal memory allocation fails. In the case, DAMON may run with the partially updated damon_ctx. This can result in unexpected behaviors including even NULL pointer dereference in case of damos_commit_dests() failure [1]. Such allocation failure is arguably too small to fail, so the real world impact would be rare. But, given the bad consequence, this needs to be fixed. Avoid such partially-committed (maybe-corrupted) damon_ctx use by saving the damon_commit_ctx() failure on the damon_ctx object. For this, introduce damon_ctx->maybe_corrupted field. damon_commit_ctx() sets it when it is failed. kdamond_call() checks if the field is set after each damon_call_control->fn() is executed. If it is set, ignore remaining callback requests and return. All kdamond_call() callers including kdamond_fn() also check the maybe_corrupted field right after kdamond_call() invocations. If the field is set, break the kdamond_fn() main loop so that DAMON sill doesn't use the context that might be corrupted. [sj@kernel.org: let kdamond_call() with cancel regardless of maybe_corrupted] Link: https://lkml.kernel.org/r/20260320031553.2479-1-sj@kernel.org Link: https://sashiko.dev/#/patchset/20260319145218.86197-1-sj%40kernel.org Link: https://lkml.kernel.org/r/20260319145218.86197-1-sj@kernel.org Link: https://lore.kernel.org/20260319043309.97966-1-sj@kernel.org [1] Fixes: 3301f1861d34 ("mm/damon/sysfs: handle commit command using damon_call()") Signed-off-by: SeongJae Park Cc: [6.15+] Signed-off-by: Andrew Morton (cherry picked from commit 26f775a054c3cda86ad465a64141894a90a9e145) Signed-off-by: SeongJae Park --- include/linux/damon.h | 7 +++++++ mm/damon/core.c | 9 ++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/damon.h b/include/linux/damon.h index 33e59d53d9f1..e44ec9d76771 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -806,7 +806,14 @@ struct damon_ctx { struct damos_walk_control *walk_control; struct mutex walk_control_lock; + /* + * indicate if this may be corrupted. Currentonly this is set only for + * damon_commit_ctx() failure. + */ + bool maybe_corrupted; + /* public: */ + /* Working thread of the given DAMON context */ struct task_struct *kdamond; struct mutex kdamond_lock; diff --git a/mm/damon/core.c b/mm/damon/core.c index ba3b7ff8ecf4..0464ef163b7c 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1241,6 +1241,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src) { int err; + dst->maybe_corrupted = true; if (!is_power_of_2(src->min_region_sz)) return -EINVAL; @@ -1266,6 +1267,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src) dst->addr_unit = src->addr_unit; dst->min_region_sz = src->min_region_sz; + dst->maybe_corrupted = false; return 0; } @@ -2610,10 +2612,11 @@ static void kdamond_call(struct damon_ctx *ctx, bool cancel) complete(&control->completion); } else if (control->canceled && control->dealloc_on_cancel) { kfree(control); - continue; } else { list_add(&control->list, &repeat_controls); } + if (!cancel && ctx->maybe_corrupted) + break; } control = list_first_entry_or_null(&repeat_controls, struct damon_call_control, list); @@ -2646,6 +2649,8 @@ static int kdamond_wait_activation(struct damon_ctx *ctx) kdamond_usleep(min_wait_time); kdamond_call(ctx, false); + if (ctx->maybe_corrupted) + return -EINVAL; damos_walk_cancel(ctx); } return -EBUSY; @@ -2731,6 +2736,8 @@ static int kdamond_fn(void *data) * kdamond_merge_regions() if possible, to reduce overhead */ kdamond_call(ctx, false); + if (ctx->maybe_corrupted) + break; if (!list_empty(&ctx->schemes)) kdamond_apply_schemes(ctx); else -- 2.47.3