linux-kernel - Re: commit 7b025f3f85ed causes NULL pointer dereference

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Message-ID: <87a58qv0tn.ffs@tglx>
Date: Tue, 08 Apr 2025 22:46:12 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Bert Karwatzki <spasswolf@....de>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
 James.Bottomley@...senPartnership.com, Jonathan.Cameron@...wei.com,
 allenbh@...il.com, d-gole@...com, dave.jiang@...el.com,
 haiyangz@...rosoft.com, jdmason@...zu.us, kristo@...nel.org,
 linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
 linux-scsi@...r.kernel.org, logang@...tatee.com,
 manivannan.sadhasivam@...aro.org, martin.petersen@...cle.com,
 maz@...nel.org, mhklinux@...look.com, nm@...com, ntb@...ts.linux.dev,
 peterz@...radead.org, ssantosh@...nel.org, wei.huang2@....com,
 wei.liu@...nel.org, spasswolf@....de
Subject: Re: commit 7b025f3f85ed causes NULL pointer dereference

On Tue, Apr 08 2025 at 18:20, Bert Karwatzki wrote:
> Am Dienstag, dem 08.04.2025 um 17:29 +0200 schrieb Thomas Gleixner:
>> > Can you please decode the lines please via:
>> >
>> >     scripts/faddr2line vmlinux msi_domain_first_desc+0x4/0x30
>> >     scripts/faddr2line vmlinux msix_setup_interrupts+0x23b/0x280
>>
>
> I had to recompile with CONFIG_DEBUG_INFO=Y, and reran the test, the calltrace
> is identical.
>
> $ scripts/faddr2line vmlinux msi_domain_first_desc+0x4/0x30
> msi_domain_first_desc+0x4/0x30:
> msi_domain_first_desc at kernel/irq/msi.c:400
>
> So it seems msi_domain_first_desc() is called with dev = NULL.

Yup

> $ scripts/faddr2line vmlinux msix_setup_interrupts+0x23b/0x280
> msix_setup_interrupts+0x23b/0x280:
> msix_update_entries at drivers/pci/msi/msi.c:647 (discriminator 1)

Aaarg. The patch below should fix that.

Thanks,

        tglx
---
diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
index 4027abcafe7a..77cc27e45b66 100644
--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -680,8 +680,8 @@ static int __msix_setup_interrupts(struct pci_dev *__dev, struct msix_entry *ent
 	if (ret)
 		return ret;
 
-	retain_ptr(dev);
 	msix_update_entries(dev, entries);
+	retain_ptr(dev);
 	return 0;
 }