Re: NULL pointer dereference: IP: [<f828a00c>] sr_runtime_suspend+0xc/0x20 [sr_mod]

[Paul Menzel <paul.menzel@giantmonkey.de>]

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Package: linux-image-4.2.0-1-686-pae
Version: 4.2.3-2
Severity: important


Dear Linux SCSI folks,


please don’t include the address submit@bugs.debian.org in your reply.


Am Freitag, den 16.10.2015, 03:05 +0200 schrieb Paul Menzel:

> using Debian Sid/unstable with Linux 4.2.3-1 upgrading from systemd
> 227-1 to 227-2 [1] and other packages, the system doesn’t start up
> anymore and the /dev/md1 device doesn’t seem to be found and I am
> dropped into shell from initramfs (BusyBox).
> 
> Only having wireless LAN and no serial or USB debug capabilities, and
> mount a USB storage device did not work, I manually copied the beginning
> of the Oops.
> 
> ```
> BUG: unable to handle kernel NULL pointer dereference at 00000014
> IP: [<f828a00c>] sr_runtime_suspend+0xc/0x20 [sr_mod]
> *pdpt = 000000003696e001 *pde = 000000000000000000
> Oops: 0000 [#1] SMB
> Modules linked in: sd_mod(+) sr_mod(+) cdrom ata_generic ohci_pci ahci libahci pata_amd firwire_ohci firewire_core crc_iti_t forcedeth libata scsi_mod ohci_hcd ehci_pci ehci_hcd usbcore usb_common fan thermal thermal_sys floppy(+)
> CPU: 1 PID: 73 Comm: systemd-udevd Not tainted 4.2.0-1-686-pae #1 Debian 4.2.3-1
> Hardware name: Packard Bell imedia S3210/WMCP78M, BIOs P01-B2 11/06/2009
> task: f68dd040 ti: f6988000 task.ti: f6988000
> EIP: 0060:[<fh28a00c>] EFLAGS: 00010246 CPU: 1
> EIP is at sr_runtime_suspend+0xc/0x20 [sr_mod]
> EAX: 00000000 EBX: f6a30cd8 ECX: f6c03d2c EDX: 00000000
> ESI: 00000000 EDI: f828e100 EBP: f6989ba8 ESP: f6989b88
>  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
> CR0: 8005003b CR2: 00000014 CR3: 3696d780 CR4: 000006f0
> Stack:
>  af83346c3 00000000 00000001 fffffff5 f6a7d150 f6a30cd8 f6a30d3c 00000000
>  f6989bbc c1390cb7 f6a30cd8 f8334660 00000000 f6989bd0 c1390d0f f6a30cd8
>  f8334660 00000000 f6989c0c c13916cb f694a614 f68dd040 00000000 00000008
> Call Trace:
>  […] ? scsi_runtime_suspend+0x63/0xa0 [scsi_mod]
>  […] ? __rpm_callback+0x27/0x60
> […]
> ```
> 
> I tried also to boot with Linux 4.1 and it fails the same way.
> 
> Is that a known problem and has been fixed in the mean time? It’d be
> great if you helped me getting the system to boot again. Please tell me
> if you need more information to debug this issue and I’ll do my best to
> get it.

Ben Hutchings asked me to test the patch below to get more debug
information.

```
diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 8bd54a6..dd5b5b2 100644
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -144,6 +144,12 @@ static int sr_runtime_suspend(struct device *dev)
 {
 	struct scsi_cd *cd = dev_get_drvdata(dev);
 
+	if (WARN_ON(!cd)) {
+		pr_info("%s: cd == NULL; power.usage_count = %d\n",
+			__func__, atomic_read(&dev->power.usage_count));
+		return 0;
+	}
+
 	if (cd->media_present)
 		return -EBUSY;
 	else
@@ -652,7 +658,13 @@ static int sr_probe(struct device *dev)
 	struct scsi_cd *cd;
 	int minor, error;
 
-	scsi_autopm_get_device(sdev);
+	error = scsi_autopm_get_device(sdev);
+	if (error) {
+		pr_err("%s: scsi_autopm_get_device returned %d\n",
+		       __func__, error);
+		return error;
+	}
+
 	error = -ENODEV;
 	if (sdev->type != TYPE_ROM && sdev->type != TYPE_WORM)
 		goto fail;
@@ -719,6 +731,9 @@ static int sr_probe(struct device *dev)
 	if (register_cdrom(&cd->cdi))
 		goto fail_put;
 
+	pr_info("%s: power.usage_count = %d\n",
+		__func__, atomic_read(&dev->power.usage_count));
+
 	/*
 	 * Initialize block layer runtime PM stuffs before the
 	 * periodic event checking request gets started in add_disk.
```

I’ll try that as soon as a spare drive has arrived, where I can copy the
data to as a backup.

More thoughts are welcome! Especially, if that error suggests a failing
drive or not.


Thanks,

Paul


> [1] http://metadata.ftp-master.debian.org/changelogs//main/s/systemd/systemd_227-2_changelog
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Geschäftsführer Adrian Fuhrmann, Lion Vollnhals und Paul Menzel

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