On Sat, Jun 20, 2020 at 10:11:46AM -0700, Bart Van Assche wrote: > On 2020-06-19 13:47, Luis Chamberlain wrote: > > Be pedantic on removal as well and hold the mutex. > > This should prevent uses of addition while we exit. > > > > Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> > > Reviewed-by: Christoph Hellwig <hch@xxxxxx> > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > > --- > > drivers/block/loop.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > > index c33bbbfd1bd9..d55e1b52f076 100644 > > --- a/drivers/block/loop.c > > +++ b/drivers/block/loop.c > > @@ -2402,6 +2402,8 @@ static void __exit loop_exit(void) > > > > range = max_loop ? max_loop << part_shift : 1UL << MINORBITS; > > > > + mutex_lock(&loop_ctl_mutex); > > + > > idr_for_each(&loop_index_idr, &loop_exit_cb, NULL); > > idr_destroy(&loop_index_idr); > > > > @@ -2409,6 +2411,8 @@ static void __exit loop_exit(void) > > unregister_blkdev(LOOP_MAJOR, "loop"); > > > > misc_deregister(&loop_misc); > > + > > + mutex_unlock(&loop_ctl_mutex); > > } > > > > module_init(loop_init); > > Is try_module_get(fops->owner) called before a loop device is opened and > is module_put(fops->owner) called after a loop device is closed? Does > that mean that it is impossible to unload the loop driver while a loop > device is open? Does that mean that the above patch is not necessary or > did I perhaps miss something? That's not the only way to add or remove the loop module though. You may add/remove it manually. And again, as mentioned in the commit log, I couldn't trigger a race myself, however this seemed the more pedantic and careful strategy we can take. Note: this will bring you sanity if you try to figure out *why* we still get: [235530.144343] debugfs: Directory 'loop0' with parent 'block' already present! [235530.149477] blktrace: debugfs_dir not present for loop0 so skipping [235530.232328] debugfs: Directory 'loop0' with parent 'block' already present! [235530.238962] blktrace: debugfs_dir not present for loop0 so skipping If you run run_0004.sh from break-blktrace [0]. Even with all my patches merged we still run into this. And so the bug lies within the block layer or on the driver. I haven't been able to find the issue yet. [0] https://github.com/mcgrof/break-blktrace Luis
