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 6016744D01E; Tue, 16 Jun 2026 15:40:48 +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=1781624449; cv=none; b=Us4T48n4MM+ln70blUZpLpUeb1eSX6mBE38j6AP29gq+qG5T8HQ4R8a6655Uac/NZYrU1GK6h2xey8xaXrLpfKkaf60gUlMesHkInNp7V4dEi0VAvR3IyZDWH2LUgdCRg/RliYZCF3nCm015uG+vSC2FDcmM/11iY+J6eg94mvI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781624449; c=relaxed/simple; bh=VMZDBK5lYTxe3yrY0NocEQ4e8cTZXMHCmd8UrEoD6uc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=A5NKQiP+Nigkt0dac0VQWcyTmM8dx0kr/fbXW5axz32FP6R+KWrL6KJqnQjquzTTnNzWjuPyXkl3aFpzHBpjkNXOkrivDzWD056dVQA0EIDn+3G7ZRHPG0fsz1FTJ/m4vG+dCSiqmfRn94lOT2WV9bvG+jTCOTcqMRqvTguu9aw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=SHVmoUSz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="SHVmoUSz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 697BE1F000E9; Tue, 16 Jun 2026 15:40:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781624448; bh=NNZ1GDsRRyVxnze96yu2F76elkxTK9DJB7XreqDRXl4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=SHVmoUSzTn2vCMptk2Ad6F7tDVifJugdUIPVifLhYfRh/EdxwoMB2lKTGjMo8+AYS R8cg0fiTf5Ovm4GfFDbPf4A8f9p4WFTGpx6D6u1qEapTLedbfqw8ujo6E6jotSitPD EvswN4K0+mFoF8LzJ2z0D54GaAnQGXQQchshk4Ws= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Shakeel Butt , Chris Mason , Kairui Song , Muchun Song , Dave Chinner , Johannes Weiner , Roman Gushchin , Andrew Morton Subject: [PATCH 7.0 305/378] mm/list_lru: drain before clearing xarray entry on reparent Date: Tue, 16 Jun 2026 20:28:56 +0530 Message-ID: <20260616145126.213771637@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145109.744539446@linuxfoundation.org> References: <20260616145109.744539446@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shakeel Butt commit 98733f3f0becb1ae0701d021c1748e974e5fa55c upstream. memcg_reparent_list_lrus() clears the dying memcg's xarray entry with xas_store(&xas, NULL) before reparenting its per-node lists into the parent. This opens a window where a concurrent list_lru_del() arriving for the dying memcg sees xa_load() == NULL, walks to the parent in lock_list_lru_of_memcg(), takes the parent's per-node lock, and calls list_del_init() on an item still physically linked on the dying memcg's list. If another in-flight thread holds the dying memcg's per-node lock at the same moment (another list_lru_del, or a list_lru_walk_one running an isolate callback), both threads modify ->next/->prev pointers on the same physical list under different locks. Adjacent items can corrupt each other's links. Fix it by reversing the order: reparent each per-node list and mark the child's list lru dead and then clear the xarray entry. Any concurrent list_lru op that finds the still-set xarray entry either takes the dying memcg's per-node lock (synchronizing with the drain) or sees LONG_MIN and walks to the parent, where the items now live. Link: https://lore.kernel.org/20260601161501.1444829-1-shakeel.butt@linux.dev Fixes: fb56fdf8b9a2 ("mm/list_lru: split the lock to per-cgroup scope") Signed-off-by: Shakeel Butt Reported-by: Chris Mason Reviewed-by: Kairui Song Acked-by: Muchun Song Cc: Dave Chinner Cc: Johannes Weiner Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/list_lru.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -472,26 +472,29 @@ void memcg_reparent_list_lrus(struct mem mutex_lock(&list_lrus_mutex); list_for_each_entry(lru, &memcg_list_lrus, list) { struct list_lru_memcg *mlru; - XA_STATE(xas, &lru->xa, memcg->kmemcg_id); /* - * Lock the Xarray to ensure no on going list_lru_memcg - * allocation and further allocation will see css_is_dying(). + * css_is_dying() check in memcg_list_lru_alloc() avoids + * allocating a new mlru since CSS_DYING is already set for this + * memcg a rcu grace period ago. */ - xas_lock_irq(&xas); - mlru = xas_store(&xas, NULL); - xas_unlock_irq(&xas); + mlru = xa_load(&lru->xa, memcg->kmemcg_id); if (!mlru) continue; /* - * With Xarray value set to NULL, holding the lru lock below - * prevents list_lru_{add,del,isolate} from touching the lru, - * safe to reparent. + * Reparent each per-node list and mark the child dead + * (LONG_MIN) before clearing xarray entry otherwise a + * concurrent list_lru_del() may corrupt the list if it arrives + * after xarray clear but before reparenting as + * lock_list_lru_of_memcg will acquire parent's lock while the + * item is still on child's list. */ for_each_node(i) memcg_reparent_list_lru_one(lru, i, &mlru->node[i], parent); + xa_erase_irq(&lru->xa, memcg->kmemcg_id); + /* * Here all list_lrus corresponding to the cgroup are guaranteed * to remain empty, we can safely free this lru, any further