On Wed, Apr 15, 2020 at 12:38:26PM -0500, Eric Sandeen wrote: > On 4/13/20 11:18 PM, Luis Chamberlain wrote: > > On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory") > > merged on v4.12 Omar fixed the original blktrace code for request-based > > drivers (multiqueue). This however left in place a possible crash, if you > > happen to abuse blktrace in a way it was not intended. > > > > Namely, if you loop adding a device, setup the blktrace with BLKTRACESETUP, > > forget to BLKTRACETEARDOWN, and then just remove the device you end up > > with a panic: > > I think this patch makes this all cleaner anyway, but - without the apparent > loop bug mentioned by Bart which allows removal of the loop device while blktrace > is active (if I read that right), can this still happen? I have not tested that, but some modifications of the break-blktrace program could enable us to test that, however I don't think the race would be possible after patch 3/5 "blktrace: refcount the request_queue during ioctl" is merged, as removal then a pending blktrace would refcount the request_queue and the removal would have to wait until the refcount is decremeneted, until after the blktrace ioctl. Luis