linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Make use of cached 'epc_features' in pci_epf_test_core

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Message-ID: <20240418065308.GG2861@thinkpad>
Date: Thu, 18 Apr 2024 12:23:08 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Niklas Cassel <cassel@...nel.org>
Cc: Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Make use of cached
 'epc_features' in pci_epf_test_core_init()

On Thu, Apr 18, 2024 at 08:46:47AM +0200, Niklas Cassel wrote:
> On Thu, Apr 18, 2024 at 11:13:19AM +0530, Manivannan Sadhasivam wrote:
> > On Wed, Apr 17, 2024 at 07:49:45PM +0200, Niklas Cassel wrote:
> > > On Wed, Apr 17, 2024 at 10:47:25PM +0530, Manivannan Sadhasivam wrote:
> > > > Instead of getting the epc_features from pci_epc_get_features() API, use
> > > > the cached pci_epf_test::epc_features value to avoid the NULL check. Since
> > > > the NULL check is already performed in pci_epf_test_bind(), having one more
> > > > check in pci_epf_test_core_init() is redundant and it is not possible to
> > > > hit the NULL pointer dereference. This also leads to the following smatch
> > > > warning:
> > > > 
> > > > drivers/pci/endpoint/functions/pci-epf-test.c:784 pci_epf_test_core_init()
> > > > error: we previously assumed 'epc_features' could be null (see line 747)
> > > > 
> > > > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > > > Closes: https://lore.kernel.org/linux-pci/024b5826-7180-4076-ae08-57d2584cca3f@moroto.mountain/
> > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > 
> > > I think you forgot:
> > > Fixes: a01e7214bef9 ("PCI: endpoint: Remove "core_init_notifier" flag")
> > > 
> > 
> > No, that's not the correct fixes tag I suppose. This redudant check is
> > introduced by commit, 5e50ee27d4a5 ("PCI: pci-epf-test: Add support to defer
> > core initialization") and this commit removes the redundant check (fixing smatch
> > warning is a side effect). So if the fixes tag needs to be added, then this
> > commit should be referenced.
> 
> Well, you have a Closes: tag that links to a bug report about a smatch
> warning that was introduced with 5e50ee27d4a5 ("PCI: pci-epf-test: Add
> support to defer core initialization").
> 
> So if you want to reference another commit, then you should probably
> drop the Closes: tag.
> 

Then checkpatch will complain... But I think I can keep the two tags? One is for
fixing the redudant check and another is for the smatch warning reported.

> 
> > 
> > > 

[...]

> > > That way, we assign msi_capable/msix_capable just before the if-statement
> > > where it is used. (Which matches how we already assign msix_capable just
> > > before the if-statement in pci_epf_test_alloc_space().)
> > > 
> > 
> > Ok, if we go with this pattern, then pci_epf_test_set_bar() also needs to be
> > updated.
> 
> pci_epf_test_set_bar() ? I presume that you mean pci_epf_test_alloc_space().
> 

Oops. I referred from an old branch.

> How about a 1/2 patch that modifies pci_epf_test_core_init() and Closes: the
> bug report, and a 2/2 patch that modifies pci_epf_test_alloc_space() ?
> 

Yes, that's the plan.

- Mani

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