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SubjectRe: [PATCH v6 6/6] blktrace: fix debugfs use after free
On Tue, Jun 09, 2020 at 05:29:22PM +0000, Luis Chamberlain wrote:
> Is scsi-generic is the only unwanted ugly child blktrace has to deal
> with? For some reason I thought drivers/md/md.c was one but it seems
> like it is not. Do we have an easy way to search for these? I think
> this would just affect how we express the comment only.

grep for blk_trace_setup. For all blk devices that setup comes in
through the block device ioctl path, and that relies on having a
struct block_device and queue. sg on the other hand calls
blk_trace_setup directly with a NULL bdev argument.

> > */
> > - dir = q->sg_debugfs_dir;
> > + dir = debugfs_create_dir(buts->name, blk_debugfs_root);
> > + bt->dir = dir;
>
> The other chicken and egg problem to consider at least in the comments
> is that the debugfs directory for these types of devices *have* an
> exposed path, but the data structure is rather opaque to the device and
> even blktrace. Fortunately given the recent set of changes around the
> q->blk_trace and clarifications around its use we have made it clear now
> that so long as hold the q->blk_trace_mutex *and* check q->blk_trace we
> *should* not race against two separate creations of debugfs directories,
> so I think this is safe, so long as these indpendent drivers don't end
> up re-using the same path for some other things later in the future, and
> since we have control over what goes under debugfsroot block / I think
> we should be good.
>
> But I think that the concern for race on names may still be worth
> explaining a bit here.

Feel free to add more comments, but please try to keep them short
and crisp. At the some point long comments really distract from what
is going on.

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