From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A61604A206E for ; Wed, 2 Sep 2026 14:15:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788358555; cv=none; b=Y3gkp6Mnwyko5pjoWLgEV73ZWBqAEe/VZbPXlRMVRC8McEokJpLAOxpOICdZTH1/hH+jlIzqmpefSbarzv1tRyQOqITx+s+TYym7nf4eWO1i5kGO5l+BuBPD2mEmZmBfuv/eXty3H4ELDwp1Jg9xedXrcqzQ1bPqx/WQ3Lp0c9A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788358555; c=relaxed/simple; bh=qUI1BXj/T7Olo0+sRw14nkhwV27mKpXf5s4YiHaq1sc=; h=MIME-Version:Date:Content-Type:From:Message-ID:Subject:To:Cc: In-Reply-To:References; b=WeuFgY3EeK1C35MAP1Tlsgq02J+zqE+Qy29NnsuSqnf0RfIwsRcoQSCPyrIHxzY2nBit61sgGbTtM/+ZcRzsbBsrGUFBTWQN8N8X/1F7Wxg1UEUf+Z0JSrB8N+peu/bosuNnpxyCS0dbcsvONyWNeJ88qZPRiCbBUHmtMvA4EDE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=PsxsnBHg; arc=none smtp.client-ip=91.218.175.185 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="PsxsnBHg" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=qUI1BXj/T7Olo0+sRw14nkhwV27mKpXf5s4YiHaq1sc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788358551; v=1; x=1788963351; b=PsxsnBHgvyDIPYbEInGtPO5fZfaV22fxMKkYMRTdyN35o8/b3BqUHGLcPnXu4v3GyjDND3aA IWAw5Kml9J6YdyKBdj9pmt6ce3DgpvKTJwnreqnsPX2+quXvXRBE54rgrJ3IOyCBtttuCmMazp0 q8mKobM/hfu5qmbT3jesQA1g= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 024c0cd5b61d1bef; Wed, 02 Sep 2026 14:15:51 +0000 X-Mizu-Trace-ID: 024c0cd5b61d1bef X-Migadu-Flow: FLOW_OUT Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Wed, 02 Sep 2026 14:15:51 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: "Zqiang" Message-ID: TLS-Required: No Subject: Re: [PATCH] dlm: wait for outstanding SRCU callbacks to complete in exit paths To: "Alexander Aring" Cc: teigland@redhat.com, gfs2@lists.linux.dev, linux-kernel@vger.kernel.org, rcu@vger.kernel.org In-Reply-To: References: <20260901091836.16906-1-qiang.zhang@linux.dev> >=20 >=20Hi, >=20 >=20On Tue, Sep 1, 2026 at 5:19 AM Zqiang wrote: >=20 >=20>=20 >=20> The dlm_lowcomms_exit() and dlm_midcomms_exit() iterate over the > > srcu protected connection and node hash tables and hand each > > element to call_srcu() for deferred freeing (connection_release() > > and midcomms_node_release()). call_srcu() is asynchronous: the > > callbacks are invoked only after an SRCU grace period, which may > > happen after the exit function has already returned. > >=20 >=20> These exit functions are reached from exit_dlm() on module unload. > > Once they return, module teardown continues and the module text > > may be unloaded while call_srcu() callbacks are still pending. When > > such a callback finally runs, it executes freed module code and > > touches the static SRCU domains that are being torn down, resulting > > in a use-after-free. > >=20 >=20I thought again about this and in my opinion this is not possible as > it is already being handled by DEFINE_STATIC_SRCU() with a cleanup > handling when the module is unloaded. When the moudle unload, the srcu_module_going() will call cleanup_srcu_st= ruct() and free_percpu(ssp->sda) to release resource. but we not call srcu_barri= er(), the srcu_barrier() should be called before cleanup_srcu_struct(). > I know that srcu subsystem does a lot of magic with modules init/exit > functionality to call init_srcu_struct() and cleanup_srcu_struct(). > See >=20 >=20https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tr= ee/kernel/module/main.c?h=3Dv7.3-rc1#n2711 >=20 >=20so this patch should be reverted. If they don't use a barrier there, > the fix should be in the SRCU subsystem, but I believe the current > SRCU implementation already handles this. The srcu_barrier() need to be called, there are some description from Documentation/RCU/rcubarrier.rst: rcu_barrier() ------------- This situation can be handled by the rcu_barrier() primitive. Rather than waiting for a grace period to elapse, rcu_barrier() waits for all outstanding RCU callbacks to complete. Please note that rcu_barrier() does **not** imply synchronize_rcu(), in particular, if there are no RCU callbacks queued anywhere, rcu_barrier() is within its rights to return immediately, without waiting for anything, let alone a grace period. Pseudo-code using rcu_barrier() is as follows: 1. Prevent any new RCU callbacks from being posted. 2. Execute rcu_barrier(). 3. Allow the module to be unloaded. There is also an srcu_barrier() function for SRCU, and you of course must match the flavor of srcu_barrier() with that of call_srcu(). If your module uses multiple srcu_struct structures, then it must also use multiple invocations of srcu_barrier() when unloading that module. For example, if it uses call_rcu(), call_srcu() on srcu_struct_1, and call_srcu() on srcu_struct_2, then the following three lines of code will be required when unloading:: 1 rcu_barrier(); 2 srcu_barrier(&srcu_struct_1); 3 srcu_barrier(&srcu_struct_2); .... Thanks Zqiang >=20 >=20- Alex >=20 >=20>=20 >=20> Add an srcu_barrier() after the call_srcu() loop in each exit funct= ion > > to wait for all outstanding callbacks of the respective SRCU domain = to > > complete before returning. In dlm_midcomms_exit() the barrier is iss= ued > > before dlm_lowcomms_exit() so that node callbacks are drained prior = to > > tearing down the lower layer. > >=20 >=20> Signed-off-by: Zqiang > > --- > > fs/dlm/lowcomms.c | 1 + > > fs/dlm/midcomms.c | 1 + > > 2 files changed, 2 insertions(+) > >=20 >=20> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c > > index 2aff1c7c17de..ea8353c4638d 100644 > > --- a/fs/dlm/lowcomms.c > > +++ b/fs/dlm/lowcomms.c > > @@ -1984,4 +1984,5 @@ void dlm_lowcomms_exit(void) > > } > > } > > srcu_read_unlock(&connections_srcu, idx); > > + srcu_barrier(&connections_srcu); > > } > > diff --git a/fs/dlm/midcomms.c b/fs/dlm/midcomms.c > > index 8964164600d2..045431524494 100644 > > --- a/fs/dlm/midcomms.c > > +++ b/fs/dlm/midcomms.c > > @@ -1178,6 +1178,7 @@ void dlm_midcomms_exit(void) > > } > > } > > srcu_read_unlock(&nodes_srcu, idx); > > + srcu_barrier(&nodes_srcu); > >=20 >=20> dlm_lowcomms_exit(); > > } > > -- > > 2.17.1 > > >