On Wed, Apr 11, 2018 at 07:58:52PM -0600, Bart Van Assche wrote: > Several block drivers call alloc_disk() followed by put_disk() if > something fails before device_add_disk() is called without calling > blk_cleanup_queue(). Make sure that also for this scenario a request > queue is dissociated from the cgroup controller. This patch avoids > that loading the parport_pc, paride and pf drivers triggers the > following kernel crash: > > BUG: KASAN: null-ptr-deref in pi_init+0x42e/0x580 [paride] > Read of size 4 at addr 0000000000000008 by task modprobe/744 > Call Trace: > dump_stack+0x9a/0xeb > kasan_report+0x139/0x350 > pi_init+0x42e/0x580 [paride] > pf_init+0x2bb/0x1000 [pf] > do_one_initcall+0x8e/0x405 > do_init_module+0xd9/0x2f2 > load_module+0x3ab4/0x4700 > SYSC_finit_module+0x176/0x1a0 > do_syscall_64+0xee/0x2b0 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > > Reported-by: Alexandru Moise <00moses.alexander00@xxxxxxxxx> > Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the block cgroup controller") > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx> > Cc: Alexandru Moise <00moses.alexander00@xxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> So, this might be correct for this reported case but I don't think it's correct in general. There's no synchronization between blkcg q->lock usages and blk_cleanup_queue(). e.g. hotunplugging and shutting down a device while file operations are still in progress can easily blow this up. Thanks. -- tejun