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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3F20C433EF for ; Mon, 28 Feb 2022 22:45:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230321AbiB1WqK (ORCPT ); Mon, 28 Feb 2022 17:46:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229551AbiB1WqI (ORCPT ); Mon, 28 Feb 2022 17:46:08 -0500 Received: from mp-relay-02.fibernetics.ca (mp-relay-02.fibernetics.ca [208.85.217.137]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5EC0136EF0 for ; Mon, 28 Feb 2022 14:45:28 -0800 (PST) Received: from mailpool-fe-02.fibernetics.ca (mailpool-fe-02.fibernetics.ca [208.85.217.145]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mp-relay-02.fibernetics.ca (Postfix) with ESMTPS id 529E761649; Mon, 28 Feb 2022 22:45:28 +0000 (UTC) Received: from localhost (mailpool-mx-02.fibernetics.ca [208.85.217.141]) by mailpool-fe-02.fibernetics.ca (Postfix) with ESMTP id 399C4630E6; Mon, 28 Feb 2022 22:45:28 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at Received: from mailpool-fe-02.fibernetics.ca ([208.85.217.145]) by localhost (mail-mx-02.fibernetics.ca [208.85.217.141]) (amavisd-new, port 10024) with ESMTP id IxQ4PECvOjLV; Mon, 28 Feb 2022 22:45:27 +0000 (UTC) Received: from [192.168.48.23] (host-45-78-195-155.dyn.295.ca [45.78.195.155]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dgilbert@interlog.com) by mail.ca.inter.net (Postfix) with ESMTPSA id 61A6C630DB; Mon, 28 Feb 2022 22:45:27 +0000 (UTC) Message-ID: Date: Mon, 28 Feb 2022 17:45:26 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Reply-To: dgilbert@interlog.com Subject: Re: [PATCH 1/2] scsi: scsi_debug: silence sparse unexpected unlock warnings Content-Language: en-CA To: Damien Le Moal , linux-scsi@vger.kernel.org, "Martin K . Petersen" References: <20220225084527.523038-1-damien.lemoal@opensource.wdc.com> <20220225084527.523038-2-damien.lemoal@opensource.wdc.com> <86e4fafa-f834-6fb5-2337-314a6078a480@interlog.com> <146bfd4a-a863-cfd4-6054-1c44439caea9@opensource.wdc.com> From: Douglas Gilbert In-Reply-To: <146bfd4a-a863-cfd4-6054-1c44439caea9@opensource.wdc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2022-02-28 01:58, Damien Le Moal wrote: > On 2022/02/28 3:39, Douglas Gilbert wrote: >> On 2022-02-25 03:45, Damien Le Moal wrote: >>> The return statement inside the sdeb_read_lock(), sdeb_read_unlock(), >>> sdeb_write_lock() and sdeb_write_unlock() confuse sparse, leading to >>> many warnings about unexpected unlocks in the resp_xxx() functions. >>> >>> Modify the lock/unlock functions using the __acquire() and __release() >>> inline annotations for the sdebug_no_rwlock == true case to avoid these >>> warnings. >> >> I'm confused. The idea with sdebug_no_rwlock was that the application >> may know that the protection afforded by the driver's rwlock is not >> needed because locking is performed at a higher level (e.g. in the >> user space). Hence there is no need to use a read-write lock (or a >> full lock) in this driver to protect a read (say) against a co-incident >> write to the same memory region. So this was a performance enhancement. >> >> The proposed patch seems to be replacing a read-write lock with a full >> lock. That would be going in the opposite direction to what I intended. > > Not at all. The __acquire() and __release() calls are not locking functions. > They are annotations for sparse so that we get a correct +/-1 counting of the > lock/unlock calls. So there is no functional change here and no overhead added > when compiling without C=1 since these macros disappear without sparse. Grrr. If those functions are dummies then I think it would be reasonable if their names had a word like "fake" or "dummy" in them. That being the case: Acked-by: Douglas Gilbert Note: these patches should probably be against Martin's 5.18/scsi-staging tree as he has taken 5 or 6 of my scsi_debug patches in this cycle. > >> >> If this is the only solution, a better idea might be to drop the >> patch (in staging I think) that introduced the sdebug_no_rwlock option. >> >> The sdebug_no_rwlock option has been pretty thoroughly tested (for over >> a year) with memory to memory transfers (together with sgl to sgl >> additions to lib/scatterlist.h). Haven't seen any unexplained crashes >> that I could trace to this lack of locking. OTOH I haven't measured >> any improvement of the copy speed either, that may be because my tests >> are approaching the copy bandwidth of the ram. >> >> >> Does sparse understand guard variables (e.g. like 'bool lock_taken')? >> From what I've seen with sg3_utils Coverity doesn't, leading to many false >> reports. >> >> Doug Gilbert >> >>> Signed-off-by: Damien Le Moal >>> --- >>> drivers/scsi/scsi_debug.c | 68 +++++++++++++++++++++++++-------------- >>> 1 file changed, 44 insertions(+), 24 deletions(-) >>> >>> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c >>> index 0d25b30922ef..f4e97f2224b2 100644 >>> --- a/drivers/scsi/scsi_debug.c >>> +++ b/drivers/scsi/scsi_debug.c >>> @@ -3167,45 +3167,65 @@ static int prot_verify_read(struct scsi_cmnd *scp, sector_t start_sec, >>> static inline void >>> sdeb_read_lock(struct sdeb_store_info *sip) >>> { >>> - if (sdebug_no_rwlock) >>> - return; >>> - if (sip) >>> - read_lock(&sip->macc_lck); >>> - else >>> - read_lock(&sdeb_fake_rw_lck); >>> + if (sdebug_no_rwlock) { >>> + if (sip) >>> + __acquire(&sip->macc_lck); >>> + else >>> + __acquire(&sdeb_fake_rw_lck); >>> + } else { >>> + if (sip) >>> + read_lock(&sip->macc_lck); >>> + else >>> + read_lock(&sdeb_fake_rw_lck); >>> + } >>> } >>> >>> static inline void >>> sdeb_read_unlock(struct sdeb_store_info *sip) >>> { >>> - if (sdebug_no_rwlock) >>> - return; >>> - if (sip) >>> - read_unlock(&sip->macc_lck); >>> - else >>> - read_unlock(&sdeb_fake_rw_lck); >>> + if (sdebug_no_rwlock) { >>> + if (sip) >>> + __release(&sip->macc_lck); >>> + else >>> + __release(&sdeb_fake_rw_lck); >>> + } else { >>> + if (sip) >>> + read_unlock(&sip->macc_lck); >>> + else >>> + read_unlock(&sdeb_fake_rw_lck); >>> + } >>> } >>> >>> static inline void >>> sdeb_write_lock(struct sdeb_store_info *sip) >>> { >>> - if (sdebug_no_rwlock) >>> - return; >>> - if (sip) >>> - write_lock(&sip->macc_lck); >>> - else >>> - write_lock(&sdeb_fake_rw_lck); >>> + if (sdebug_no_rwlock) { >>> + if (sip) >>> + __acquire(&sip->macc_lck); >>> + else >>> + __acquire(&sdeb_fake_rw_lck); >>> + } else { >>> + if (sip) >>> + write_lock(&sip->macc_lck); >>> + else >>> + write_lock(&sdeb_fake_rw_lck); >>> + } >>> } >>> >>> static inline void >>> sdeb_write_unlock(struct sdeb_store_info *sip) >>> { >>> - if (sdebug_no_rwlock) >>> - return; >>> - if (sip) >>> - write_unlock(&sip->macc_lck); >>> - else >>> - write_unlock(&sdeb_fake_rw_lck); >>> + if (sdebug_no_rwlock) { >>> + if (sip) >>> + __release(&sip->macc_lck); >>> + else >>> + __release(&sdeb_fake_rw_lck); >>> + } else { >>> + if (sip) >>> + write_unlock(&sip->macc_lck); >>> + else >>> + write_unlock(&sdeb_fake_rw_lck); >>> + } >>> } >>> >>> static int resp_read_dt0(struct scsi_cmnd *scp, struct sdebug_dev_info *devip) >> > >