On Wed, Jan 18, 2017 at 06:33:56AM +0000, linux-kernel-dev wrote: > >From: Jakub Kicinski [mailto:jakub.kicin...@netronome.com] > >Sent: Dienstag, 17. Januar 2017 22:18 > > > >On Tue, Jan 17, 2017 at 12:53 PM, Luis R. Rodriguez <mcg...@kernel.org> > >wrote: > >> On Tue, Jan 17, 2017 at 10:04:20AM -0800, Jakub Kicinski wrote: > >>> On Tue, Jan 17, 2017 at 9:30 AM, Luis R. Rodriguez <mcg...@kernel.org> > >wrote: > >>> > On Tue, Jan 17, 2017 at 08:30:37AM -0800, Jakub Kicinski wrote: > >>> >> Adding a NULL-check would just paper over the > >>> >> issue and can cause trouble down the line. > >>> > > >>> > We typically bail on errors and use similar code to bail out, and we > >>> > typically do these things. Here its no different. The *real* issue > >>> > is the fact that we have a waiting timeout which can fail race against > >>> > a user imposed error out on the sysfs interface. There is one catch: > >>> > > >>> > We already lock with the big fw_lock and use this to be able to check > >>> > for the status of the fw, so once aborted we technically should not have > >>> > to abort again. A proper way to address then this would have been to > >check > >>> > for the status of the fw prior to aborting again given we also lock on > >>> > the > >>> > big fw_lock. A problem with this though is the status is part of the buf > >>> > which is set to NULL after we are done aborting. > >>> > >>> Yes, I've seen that too :\ This race seems to have been there prior > >>> to 4.9, though. I guess we could fix both issues with the NULL-check > >>> although I would prefer if we had both patches. > >>> > >>> FWIW I think the NULL-check could be put in the existing conditional: > >>> > >>> * There is a small window in which user can write to 'loading' > >>> * between loading done and disappearance of 'loading' > >>> */ > >>> - if (fw_state_is_done(&buf->fw_st)) > >>> + if (!buf || fw_state_is_done(&buf->fw_st)) > >>> return; > >>> > >>> list_del_init(&buf->pending_list); > >>> > >>> Note that the comment above seems to be mentioning the race we're > >>> trying to solve. > >> > >> Right, I think another approach is to *enable* the state of the buf > >> to be used to avoid further use on the sysfs iterface instead. Fortunately > >> other sysfs interfaces already use fw_state_is_done() to bail out, > >> so all that would be needed I think would be: > >> > >> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c > >> index b9ac348e8d33..30ccf7aea3ca 100644 > >> --- a/drivers/base/firmware_class.c > >> +++ b/drivers/base/firmware_class.c > >> @@ -558,9 +558,6 @@ static void fw_load_abort(struct firmware_priv > >*fw_priv) > >> struct firmware_buf *buf = fw_priv->buf; > >> > >> __fw_load_abort(buf); > >> - > >> - /* avoid user action after loading abort */ > >> - fw_priv->buf = NULL; > >> } > >> > >> static LIST_HEAD(pending_fw_head); > >> @@ -713,7 +710,7 @@ static ssize_t firmware_loading_store(struct device > >*dev, > >> > >> mutex_lock(&fw_lock); > >> fw_buf = fw_priv->buf; > >> - if (!fw_buf) > >> + if (!fw_buf || fw_state_is_aborted(&fw_buf->fw_st)) > >> goto out; > >> > >> switch (loading) { > > > >IMHO this one is nice! I think you can even drop the !fw_buf check in > >this case because AFAICS the only case where fw_buf is set to NULL is > >in the abort function. > > > I can confirm, that patch looks nice and is working for my setup, even > without the !fw_buf. > Feel free to grab everything you need from my commit log, if it helps. > Unfortunately there is a crazy spam filter between us, so you can't rely on > me.
OK I'll submit this version with both your Reported-and-Tested-by. Luis
