From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 258ED243376 for ; Tue, 16 Jun 2026 00:33:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781570037; cv=none; b=WKuue3nRCRgsM8IUkkL/ImFveKNmgth+yFYrOjp7V4MRsymaJ+nK/GZr5MpRYSAgXhf0a2TwgllWss/Nq+ox33fQfn9sJM+jdFxqKthlc/uONbsMwyMBN6tjS8RJUxZIJ9wTm/qq8xc+G54+udK1WzUtmynWkadqi21dGXzP+j4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781570037; c=relaxed/simple; bh=dhG0qTmxRJCFeDxS2zULR97K9iw81i0kKqjbWCkeJTU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TfUg1qxeK4zjBrePzH0MUE/dyFcA5rEeq4R8vQmyeY7ExXanDunlD4INlF37bXeisCWetn/WWI0qBYI04oUS2iu4f0W+1uin1kKUTW7UUXo91TBdiVt37NBj/UBjZitzZjxAISoBoOVS/ula7K6gO8jVQYDprVYuHNViSsIa3OM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g8PKPYbT; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g8PKPYbT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A3771F000E9; Tue, 16 Jun 2026 00:33:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781570036; bh=RC5cz7R8sad6+KQpxwVwOduOOhcwydpgcJc3JovOP84=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=g8PKPYbTgYCPastN3gvC4Unv51An6mB+b0rCw9FTkDKC6+RhdfBKYzMktvccs1YQU zRtMFsLa40pP40cXYw4s/ifLFMFDqMZg8TcjW1Ku3bRYlZyKTHnqEEtp/GuSlCTe6J JPA9RvqbYpfUqr4Hl7K5V+SBUgxz3ikWN2ycetOEj2jhYYW8+U50C49LFInQbSeYrP toGfSgaRxIU8BAh+libXjRNlK0beRjS/ERULanhg84kRws5H5Id5ZAXOkuZ7RFf8he JBvN8tw4dtO/Na0ERQeD3gvga/3Y0wig5Ovrofjz2WSJT0Hj4RSA7hOIqIc+hPzePs y0k9ABtwPmVSg== From: SeongJae Park To: Sasha Levin Cc: SeongJae Park , stable@vger.kernel.org, Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton Subject: Re: [PATCH 6.1.y] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Mon, 15 Jun 2026 17:33:45 -0700 Message-ID: <20260616003346.141166-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260615190329.2368312-1-sashal@kernel.org> References: Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Mon, 15 Jun 2026 15:03:29 -0400 Sasha Levin wrote: > From: SeongJae Park > > [ Upstream commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef ] > > damon_get_folio() speculatively calls folio_test_lru() before > folio_try_get(). The folio can get freed and reallocated to a tail page. > In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. > Remove the speculative call. > > Also mark folio_test_lru() check right after folio_try_get() success as no > more unlikely. > > The race should be rare. Also the problem can happen only if the kernel > has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue > has been made so far. This fix is based on only theoretical analysis. > That said, a bug is a bug. A similar issue was also fixed via commit > 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a > reference in next_uptodate_folio()"). I don't expect this change will > make a meaningful impact to DAMON performance in the real world, though I > will be happy to be corrected from the real world reports. > > The issue was discovered [1] by Sashiko. > > Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org > Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] > Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") > Signed-off-by: SeongJae Park > Cc: Fernand Sieber > Cc: Leonard Foerster > Cc: Shakeel Butt > Cc: # 5.15.x > Signed-off-by: Andrew Morton > Signed-off-by: Sasha Levin Thank you for fixing the conflict, Sasha! Reviewed-by: SeongJae Park Thanks, SJ [...]