From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B11EAC433DB for ; Thu, 21 Jan 2021 12:18:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 69BBF206ED for ; Thu, 21 Jan 2021 12:18:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731048AbhAUMSE (ORCPT ); Thu, 21 Jan 2021 07:18:04 -0500 Received: from mx.cjr.nz ([51.158.111.142]:63584 "EHLO mx.cjr.nz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728429AbhAUMRk (ORCPT ); Thu, 21 Jan 2021 07:17:40 -0500 Received: from authenticated-user (mx.cjr.nz [51.158.111.142]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: pc) by mx.cjr.nz (Postfix) with ESMTPSA id 16D8E7FD23; Thu, 21 Jan 2021 12:16:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cjr.nz; s=dkim; t=1611231412; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=e/a77pFsd8zEqKoP+D62M03PRM70OM6Ff8xg3LmEjvM=; b=0GWfVNvwjlpqXxGVZcYJRDRD8LvhwMt+oTaR6NrXRR5IJgm+jp/O6rw1l6+4EKpOzo+W4o 0CYvGbj2bcy02eJkeMTfi0H/NFM0eBLNf27y4CxGDC2eIAxuQKk4EXFAqJ2FNKjToRieIs AJCRVHYBzxI/8idOID7IPbJRlLjADJsxTO1AveOyj9HXg+sMOvs5ndgjU9IrwSLZqjGatC A+TSJ/+dzP8oLdCj7QaAuv4oNJHEriSgCZTWqO5X7Gs0+/VNlRgWyi8+zw2UMP7LIS3aUx wC9XREA3UCEMKajEsVDWjZqRSdAtNdzp19m0yoEPe+x2RFuK6KVYp6dp5pFgiQ== From: Paulo Alcantara To: =?utf-8?Q?Aur=C3=A9lien?= Aptel , Pavel Shilovsky , Steve French Cc: Ronnie Sahlberg , linux-cifs Subject: Re: [PATCH] cifs: do not fail __smb_send_rqst if non-fatal signals are pending In-Reply-To: <87y2gmk3ap.fsf@suse.com> References: <20210120043209.27786-1-lsahlber@redhat.com> <87y2gmk3ap.fsf@suse.com> Date: Thu, 21 Jan 2021 09:16:46 -0300 Message-ID: <877do6zdqp.fsf@cjr.nz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org Aur=C3=A9lien Aptel writes: > Pavel Shilovsky writes: > >> =D0=B2=D1=82, 19 =D1=8F=D0=BD=D0=B2. 2021 =D0=B3. =D0=B2 22:38, Steve Fr= ench : >>> >>> The patch won't merge (also has some text corruptions in it). This >>> line of code is different due to commit 6988a619f5b79 >>> >>> 6988a619f5b79 (Paulo Alcantara 2020-11-28 15:57:06 -0300 342) >>> cifs_dbg(FYI, "signal pending before send request\n"); >>> 6988a619f5b79 (Paulo Alcantara 2020-11-28 15:57:06 -0300 343) >>> return -ERESTARTSYS; >>> >>> if (signal_pending(current)) { >>> cifs_dbg(FYI, "signal pending before send request\n"); >>> return -ERESTARTSYS; >>> } >>> >>> See: >>> >>> Author: Paulo Alcantara >>> Date: Sat Nov 28 15:57:06 2020 -0300 >>> >>> cifs: allow syscalls to be restarted in __smb_send_rqst() >>> >>> A customer has reported that several files in their multi-threaded = app >>> were left with size of 0 because most of the read(2) calls returned >>> -EINTR and they assumed no bytes were read. Obviously, they could >>> have fixed it by simply retrying on -EINTR. >>> >>> We noticed that most of the -EINTR on read(2) were due to real-time >>> signals sent by glibc to process wide credential changes (SIGRT_1), >>> and its signal handler had been established with SA_RESTART, in whi= ch >>> case those calls could have been automatically restarted by the >>> kernel. >>> >>> Let the kernel decide to whether or not restart the syscalls when >>> there is a signal pending in __smb_send_rqst() by returning >>> -ERESTARTSYS. If it can't, it will return -EINTR anyway. >>> >>> Signed-off-by: Paulo Alcantara (SUSE) >>> CC: Stable >>> Reviewed-by: Ronnie Sahlberg >>> Reviewed-by: Pavel Shilovsky >>> >>> On Tue, Jan 19, 2021 at 10:32 PM Ronnie Sahlberg = wrote: >>> > >>> > RHBZ 1848178 >>> > >>> > There is no need to fail this function if non-fatal signals are >>> > pending when we enter it. >>> > >>> > Signed-off-by: Ronnie Sahlberg >>> > --- >>> > fs/cifs/transport.c | 2 +- >>> > 1 file changed, 1 insertion(+), 1 deletion(-) >>> > >>> > diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c >>> > index c42bda5a5008..98752f7d2cd2 100644 >>> > --- a/fs/cifs/transport.c >>> > +++ b/fs/cifs/transport.c >>> > @@ -339,7 +339,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, i= nt num_rqst, >>> > if (ssocket =3D=3D NULL) >>> > return -EAGAIN; >>> > >>> > - if (signal_pending(current)) { >>> > + if (fatal_signal_pending(current)) { >>> > cifs_dbg(FYI, "signal is pending before sending any d= ata\n"); >>> > return -EINTR; >>> > } > > I've looked up the difference > > static inline int __fatal_signal_pending(struct task_struct *p) > { > return unlikely(sigismember(&p->pending.signal, SIGKILL)); > } > > >> I have been thinking around the same lines. The original intent of >> failing the function here was to avoid interrupting packet send in the >> middle of the packet and not breaking an SMB connection. >> That's also why signals are blocked around smb_send_kvec() calls. I >> guess most of the time a socket buffer is not full, so, those >> functions immediately return success without waiting internally and >> checking for pending signals. With this change the code may break SMB > > Ah, interesting. > > I looked up the difference between fatal/non-fatal and it seems > fatal_signal_pending() really only checks for SIGKILL, but I would > expect ^C (SIGINT) to return quickly as well. > > I thought the point of checking for pending signal early was to return > quickly to userspace and not be stuck in some unkillable state. > > After reading your explanation, you're saying the kernel funcs to send > on socket will check for any signal and err early in any case. > > some_syscall() { > > if (pending_fatal_signal) <=3D=3D=3D=3D=3D if we ignore non-fatal he= re > fail_early(); > > block_signals(); > r =3D kernel_socket_send { > if (pending_signal) <=3D=3D=3D=3D they will be caught here > return error; > > ... > } > unblock_signals(); > if (r) > fail(); > ... > } > > So this patch will (potentially) trigger more reconnect (because we > actually send the packet as a vector in a loop) but I'm not sure I > understand why it returns less errors to userspace? > > Also, shouldn't we move the pending_fatal_signal check *inside* the block= ed > signal section? > > In any case I think we should try to test some of those changes given > how we have 3,4 patches trying to tweak it on top of each other. I think it would make sense to have something like diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index e9abb41aa89b..f7292c14863e 100644 --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -340,7 +340,7 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num= _rqst, =20 if (signal_pending(current)) { cifs_dbg(FYI, "signal pending before send request\n"); - return -ERESTARTSYS; + return __fatal_signal_pending(current) ? -EINTR : -ERESTARTSYS; } =20 /* cork the socket */ so that we allow signal handlers to be executed before restarting syscalls when receiving non-fatal signals, otherwise -EINTR.