/sys/fs/pstore is empty after kernel crash

[powellnorma]

When I trigger a kernel crash via echo c > /proc/sysrq-trigger, normally /sys/fs/pstore gets filled with 3 files:

sunfish:/ # ls /sys/fs/pstore/                                                                                                                                                                
console-ramoops-0  dmesg-ramoops-0  pmsg-ramoops-0

But when Magisk is installed, this folder stays empty.

What I noticed is that normally only after pin unlock pstore gets mounted:

pstore on /sys/fs/pstore type pstore (rw,seclabel,relatime)

But with magisk, something pstore related is already mounted before that stage:

pstore on /debug_ramdisk/.magisk/mirror/sys/fs/pstore type pstore (rw,seclabel,nosuid,nodev,noexec,relatime)

And after unlock:

pstore on /debug_ramdisk/.magisk/mirror/sys/fs/pstore type pstore (rw,seclabel,nosuid,nodev,noexec,relatime)
pstore on /sys/fs/pstore type pstore (rw,seclabel,relatime)

magisk.log dmesg.log

Device: Pixel4a Android version: 13 Magisk version name: 26.3 Magisk version code: 26301

[kaiyu92]

Same issue here with Pixel 4a device. /sys/fs/pstore seems to always be empty even after a kernel crash.

Device: Pixel 4a Android Version: 10 Magisk version: 26.1

[vvb2060]

I don't think it has anything to do with magisk.

[powellnorma]

I don't think it has anything to do with magisk.

I tested several times: When not using magisk /sys/fs/pstore gets filled, when using it /sys/fs/pstore stays empty.

[vvb2060]

How to panic the kernel without root?

[powellnorma]

In a debug build, one can use adb root

[vvb2060]

After you install magisk, is adb root still available?

[powellnorma]

I think so, since afaik adb root has nothing to do with magisk. Why are you asking though? If adb root does not work for you, you probably have a -user build. LineageOS usually provides -userdebug builds.

[vvb2060]

Have you tried it? If you have some magisk modules, adb root will not be available, kmsg may be for similar reasons. (You know, the device is user build now)

[powellnorma]

Have you tried it? If you have some magisk modules, adb root will not be available

Yes, adb root still works - I have just double checked it

[powellnorma]

I have found a solution that works for my device:

Add umount("/sys/fs/pstore"); before the "mirror mounting" logic:

https://github.com/topjohnwu/Magisk/blob/15e13a8d8bb61ed896df94881d63903cbfcc516b/native/src/core/bootstages.cpp#L97-L98

My guess is that the system clears up the pstore of "two mounts before" it. Because I also tried to mount it again after the mirror logic (via mount("pstore", "/sys/fs/pstore", "pstore", 0, "");), and then pstore again stays empty.

I think the best solution would be to not use MS_REC, and instead always use the fallback logic, and then skip the mirror mount if info.type == "pstore".

[yujincheng08]

Not using MS_REC is not a good solution. Maybe you should try to move pstore into somewhere unbindable, then mount mirror MS_REC and move pstore back.

[vvb2060]

After investigation, I found that if umount pstore in boot_complete and then mount pstore after unlock screen, files will exist.

[Ristovski]

~~Can confirm that same thing happens on Xiaomi Mi 11 Lite 5G NE (lisa). What exactly is the cause here?~~ Edit: This seems to have been a fluke on this device. Disregard.

[yujincheng08]

https://android.googlesource.com/kernel/msm/+/b71d012395a42ae6b58f36f5eaf460a9ff29e31a%5E%21/

[yujincheng08]

Try #7685

[vvb2060]

The pstore is decrypted when the user first unlocks device, at which point no pstore instance can exist. Decryption will fail if a pstore bind mount exists, or if a unshared process retains a pstore instance.