From: Justin Bronder <email@example.com> To: Mark Greer <firstname.lastname@example.org> Cc: Geoff Lansberry <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Jaret Cantu <email@example.com> Subject: Re: nfc: trf7970a: Prevent repeated polling from crashing the kernel Date: Tue, 20 Dec 2016 14:13:52 -0500 [thread overview] Message-ID: <20161220191352.GB23496@lasswell.members.linode.com> (raw) In-Reply-To: <20161220185905.GA5867@animalcreek.com> On 20/12/16 11:59 -0700, Mark Greer wrote: > On Tue, Dec 20, 2016 at 11:16:32AM -0500, Geoff Lansberry wrote: > > From: Jaret Cantu <firstname.lastname@example.org> > > > > Repeated polling attempts cause a NULL dereference error to occur. > > This is because the state of the trf7970a is currently reading but > > another request has been made to send a command before it has finished. > > How is this happening? Was trf7970a_abort_cmd() called and it didn't > work right? Was it not called at all and there is a bug in the digital > layer? More details please. > > > The solution is to properly kill the waiting reading (workqueue) > > before failing on the send. > > If the bug is in the calling code, then that is what should get fixed. > This seems to be a hack to work-around a digital layer bug. One of our uses of NFC is to begin polling to read a tag and then stop polling (in order to save power) until we know via user interaction that we need to poll again. This is typically many minutes later so the power saving is pretty significant. However, it's possible that a user will remove the tag before reading has completed. We also detect this case and stop polling. I can go more into this if necessary but that is what exposed a panic. You can reproduce using neard and python, in our testing it was very likely to occur in 10-100 iterations of the following.: #!/usr/bin/python import time import dbus bus = dbus.SystemBus() nfc0 = bus.get_object('org.neard', '/org/neard/nfc0') props = dbus.Interface(nfc0, 'org.freedesktop.DBus.Properties') try: props.Set('org.neard.Adapter', 'Powered', dbus.Boolean(1)) except: pass adapter = dbus.Interface(nfc0, 'org.neard.Adapter') for i in range(1000): adapter.StartPollLoop('Initiator') time.sleep(0.1) adapter.StopPollLoop() print(i) I believe the last time we tested this was around the 4.1 release. -- Justin Bronder
next prev parent reply other threads:[~2016-12-20 19:14 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-12-20 16:16 [PATCH 1/3] NFC: trf7970a: add device tree option for 27MHz clock Geoff Lansberry 2016-12-20 16:16 ` [PATCH 2/3] NFC: trf7970a: Add device tree option of 1.8 Volt IO voltage Geoff Lansberry 2016-12-21 2:23 ` Mark Greer 2016-12-21 11:47 ` Geoff Lansberry 2016-12-21 16:13 ` Mark Greer 2016-12-20 16:16 ` [PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel Geoff Lansberry 2016-12-20 18:59 ` Mark Greer 2016-12-20 19:13 ` Justin Bronder [this message] 2016-12-20 19:56 ` Mark Greer 2016-12-20 17:58 ` [PATCH 1/3] NFC: trf7970a: add device tree option for 27MHz clock Jones Desougi 2016-12-20 18:11 ` Mark Greer 2016-12-20 18:29 ` Geoff Lansberry 2016-12-20 18:35 ` Mark Greer
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20161220191352.GB23496@lasswell.members.linode.com \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --subject='Re: nfc: trf7970a: Prevent repeated polling from crashing the kernel' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).