Package: linux
Version: 6.12.86-1
Severity: important
Tags: upstream

netfs_consume_read_data() calls local_bh_enable() in hard IRQ context
when reached via the cachefiles async read completion path.

The call chain is:

  nvme_irq                              [hard IRQ]
    blk_mq_end_request_batch
      iomap_dio_bio_end_io
        cachefiles_read_complete        [cachefiles]
          netfs_read_subreq_terminated  [netfs]
            netfs_consume_read_data     [netfs]
              __local_bh_enable_ip      *** WARNING ***

This fires a WARN_ON at kernel/softirq.c:386 because local_bh_enable()
is called while in hard IRQ context (PID 0, swapper, inside <IRQ>).

The issue is that netfs_consume_read_data() assumes it runs in process
or softirq context, but cachefiles_read_complete() can be called
directly from block layer IRQ completion (iomap_dio_bio_end_io), which
runs in hard IRQ context.

This triggers ~6 seconds after boot once NFS mounts with fsc come up
and the first cached reads complete from the NVMe backing store.

I have only seen this once so far. The system continued running but
cachefilesd appears to have died shortly after (possibly related).

Full trace: