Date: Fri, 15 Nov 2019 10:59:13 +0700 From: Eugene Grosbein <eugen@grosbein.net> To: Ian Lepore <ian@freebsd.org>, Daniel Braniss <danny@cs.huji.ac.il> Cc: freebsd-hackers <freebsd-hackers@freebsd.org> Subject: Re: can the hardware watchdog reboot a hung kernel? Message-ID: <eefaafea-54e0-a692-8588-a753b37b571c@grosbein.net> In-Reply-To: <ede820ea5c5f71cea2a98955d02b700b483e1899.camel@freebsd.org> References: <EC4DB495-55D0-44BB-8D6A-0301785FADC7@cs.huji.ac.il> <9cded04a-9ae1-881e-3962-7ef0322e96ed@grosbein.net> <2AD912BF-97B0-421D-B561-722D74864DC9@cs.huji.ac.il> <828605fef472e04311c83a7de0d1f4df429ae717.camel@freebsd.org> <BEC1714A-2361-4B62-BEB9-82808920C269@cs.huji.ac.il> <ede820ea5c5f71cea2a98955d02b700b483e1899.camel@freebsd.org>
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15.11.2019 1:19, Ian Lepore wrote: > One thing to be careful of here is multicore systems. If you have a > critical app running on a multicore system, that app can hang (maybe it > tries to read from a device that has malfunctioned and essentially gets > hung forever in a device driver that doesn't implement timeouts very > well or something). In that case, only one core is hung, so watchdogd > will be able to keep petting the dog to prevent a reboot, but since > your app is hung on a different core, you aren't really getting the > protection you need. > > The fix for that is to either turn you app into watchdogd (have it make > the periodic ioctl() calls to pet the dog), or use the '-e cmd' option > with watchdogd, and make 'cmd' be a script that somehow verifies that > your critical application is still running properly. I have not tried it myself, but there may be easier way if the app is single-process and single-threaded: use cpuset(1) to bind both of the app and watchdogd to same core.
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