NACK: [SRU][I][PATCH 0/1] kernel panic: NULL pointer dereference in wb_timer_f()

[Andrea Righi]

On Tue, Oct 19, 2021 at 05:53:08PM +0200, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1947557
> 
> [Impact]
> 
> It is possible to trigger a kernel panic with the latest impish kernel running
> systemd autopkgtest using --enable-kvm with the test instances created by
> systemd during the autotest. The panic happens in the host, not in the guest VM
> executed by systemd.
> 
> [Test case]
> 
> Add --enable-kvm to the options in test/testdata/test-functions (systemd), run
> `sudo autopkgtest . -- null`, wait for the panic to happen.
> 
> [Fix]
> 
> https://lore.kernel.org/lkml/YW6N2qXpBU3oc50q@arighi-desktop/T/#u
> 
> [Regression potential]
> 
> The fix is addressing a race in the block layer (in the buffered write
> throttling code - block/blk-wbt.c) between a disk being released and the timer
> callback that periodically checks if the latency for a specific block device
> has been exceeded. If the fix is not correct we may still have a race in this
> code, that can still show potential kernel panics in the block layer subsystem.

The upstream fix doesn't apply correctly to the impish kernel. I'll send
a v2 after testing the fix properly with the impish kernel. Sorry for
the noise.

-Andrea