From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f171.google.com (mail-oi1-f171.google.com [209.85.167.171]) (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 E0413258F for ; Fri, 2 Jun 2023 14:32:37 +0000 (UTC) Received: by mail-oi1-f171.google.com with SMTP id 5614622812f47-39a505b901dso1841696b6e.0 for ; Fri, 02 Jun 2023 07:32:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1685716357; x=1688308357; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=6NwA907vGnrNpaOFyWDRDxSy5v1vFxmBWhlUfMES2kw=; b=EauV+zfSnBg6r0ozgcM9FVLsm5gQCUXgiYyfYePz+nQ/L81vRnwKSIX3WIdM4BmfS2 Y6Q0se655hmMB+A2zm5Ipm6ukstFJH/l3WWIKs6vgRvCR18zZL6inolAzhr0+/y2NZGd wLDgV6XS3o9gg12dJMji52ozOCvPoJ1oejgSpyUaETeJQtItQiIplDI7sgX65PF7k5G4 6CGEq9XCateFJruI6vXJDAEmQOFsSgegr4aLlAXyQ/0o/BOZtRDufrYSj2nRrD0gd/Ip HkDVzLSDdWPCV3pG3MTk58ed9yYqeyz8j4tvKpboWViVkZaPjy84wwHmnWt93wpu6fLU 6WTA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685716357; x=1688308357; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=6NwA907vGnrNpaOFyWDRDxSy5v1vFxmBWhlUfMES2kw=; b=FT99PmUCfnAW0nHr30IOGkX2Hps9+e6YNR3Nv0Y1IdIIgiia5pBMdv7OkUOIuJEhSC iE5Wqu5i1mIOXy5z4FkWIBsyXHAKBeK2/K29ZKp3H8vx1f9ikD/OE5aKXDOcE9zm7vSv qhJASJev1FNkyZCtYUz8WjX79ZMIWuvACSa3aQE5IysTOjAdj6s2KrtSx8x+QIfRBu+L 38rNcMgsLUGDy54+955OuYig38zKpEfCXh2qj5AaQE7OMaH0twYvEL5Rr+NLDzMqglXr oZUGoEcFbNa0OPb0gWSK++vvUsCRptQYcvrS+h8PmIXqdWO6YMJFnpr3kWu+JLHCsBvW g87Q== X-Gm-Message-State: AC+VfDzPUa0kpCwFLKVh1UqEl7rdhTSaOlvEI9qq9bKXQ7KeFhWkeSrI yvzdELzhrdIHYdsDQz7rKXDTKA== X-Google-Smtp-Source: ACHHUZ4V0UzJXmOaS27pn0qGqFdFCh76Hfz2jr/a0CAePlRB6y4q8OwnVaD7Jbl2aB8HCK25aVZeqQ== X-Received: by 2002:a54:408b:0:b0:39a:748f:4bbd with SMTP id i11-20020a54408b000000b0039a748f4bbdmr132133oii.15.1685716356815; Fri, 02 Jun 2023 07:32:36 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-142-68-25-194.dhcp-dynamic.fibreop.ns.bellaliant.net. [142.68.25.194]) by smtp.gmail.com with ESMTPSA id j18-20020a0ceb12000000b0061b5dbf1994sm839858qvp.146.2023.06.02.07.32.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jun 2023 07:32:36 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1q55pT-001vhW-EA; Fri, 02 Jun 2023 11:32:35 -0300 Date: Fri, 2 Jun 2023 11:32:35 -0300 From: Jason Gunthorpe To: Baolu Lu Cc: Yanfei Xu , dwmw2@infradead.org, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] iommu/vt-d: Use BUG_ON to check NULL value of 'table' Message-ID: References: <20230530092503.152926-1-yanfei.xu@intel.com> <20230530092503.152926-3-yanfei.xu@intel.com> <3e75f9de-4c67-93aa-9fb4-28da9849dd48@linux.intel.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3e75f9de-4c67-93aa-9fb4-28da9849dd48@linux.intel.com> On Wed, May 31, 2023 at 11:26:55AM +0800, Baolu Lu wrote: > On 5/30/23 5:25 PM, Yanfei Xu wrote: > > Checking NULL value of 'table' variable deserves a BUG_ON as the > > following code will trigger a crash by dereferencing the NULL > > 'table' pointer. Crash in advance with BUG_ON to avoid WARN_ON > > plus NULL pointer dereferencing can simplify the crash log. > > > > Signed-off-by: Yanfei Xu > > --- > > drivers/iommu/intel/iommu.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c > > index e98f1b122b49..8aa3bfdb7f95 100644 > > --- a/drivers/iommu/intel/iommu.c > > +++ b/drivers/iommu/intel/iommu.c > > @@ -1944,7 +1944,7 @@ static int domain_context_mapping_one(struct dmar_domain *domain, > > if (sm_supported(iommu)) { > > unsigned long pds; > > - WARN_ON(!table); > > + BUG_ON(!table); > > BUG_ON() is not recommended. Perhaps, > > if (!table) > -ENODEV; > > ? If it is not something you think needs active debugging then just let it crash on the NULL pointer deref. You get a nice backtrace from that already. The additional value of the WARN is it gives you a line number, a prettier print and it might recover more cleanly (or not, it might just crash somewhere else). Jason