Re: [PATCH RFC v3 18/36] kmsan: disable LOCK_DEBUGGING_SUPPORT

From: Steven Rostedt <rostedt@goodmis.org>
To: Alexander Potapenko <glider@google.com>
Cc: Qian Cai <cai@lca.pw>, Marco Elver <elver@google.com>,
	Eric Biggers <ebiggers@google.com>,
	Christoph Hellwig <hch@lst.de>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Harry Wentland <harry.wentland@amd.com>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Andy Lutomirski <luto@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	"David S. Miller" <davem@davemloft.net>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Eric Dumazet <edumazet@google.com>,
	Eric Van Hensbergen <ericvh@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ilya Leoshkevich <iii@linux.ibm.com>, Ingo Molnar <mingo@elte.hu>,
	Jason Wang <jasowang@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Mark Rutland <Mark.Rutland@arm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Michal Simek <monstr@monstr.eu>, Petr Mladek <pmladek@suse.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Robin Murphy <Robin.Murphy@arm.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Takashi Iwai <tiwai@suse.com>, "Theodore Ts'o" <tytso@mit.edu>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH RFC v3 18/36] kmsan: disable LOCK_DEBUGGING_SUPPORT
Date: Tue, 3 Dec 2019 13:38:15 -0500	[thread overview]
Message-ID: <20191203133815.05a020fc@gandalf.local.home> (raw)
In-Reply-To: <CAG_fn=Wvj77RHGvQz9MZdecJkcs4dKT8=3bQ89ZCTkfc7KdWfQ@mail.gmail.com>

On Tue, 3 Dec 2019 16:14:17 +0100
Alexander Potapenko <glider@google.com> wrote:

> On Tue, Dec 3, 2019 at 4:00 PM Qian Cai <cai@lca.pw> wrote:
> >
> >
> >  
> > > On Dec 3, 2019, at 9:35 AM, Alexander Potapenko <glider@google.com> wrote:
> > >
> > > At this point I don't really know why KMSAN and lockdep don't play
> > > well together, but I'm not expecting anyone to use them together
> > > either.  
> >
> > Of course people will use those together. For example, distro debug kernel variants.  
> Some tools are just not designed to work together.
> For example, you won't be able to compile the kernel with both KASAN
> and KMSAN enabled at the same time.
> 
> Lockdep doesn't require any instrumentation to work, so it _might_ be
> possible to make it work with KMSAN, but it will probably still slow
> down the things to an unacceptable level.
> I'm inclining towards disabling the two together for now, unless
> anyone is willing to address that issue.

Note, I'm much more interested in someone running with lockdep than
with KMSAN. Thus, you may not get as much use if you do not work with
lockdep. I enable lockdep first when testing out my code. If KMSAN is
not compatible, it wont get enabled.

> 
> Please let me know if you think I need to keep the link to
> https://github.com/google/kmsan/issues/57 in the Kconfig comment,
> right now it looks like:
> 
>   # KMSAN is currently incompatible with lockdep.
> 

Function tracing had lots of issues with lockdep, but I worked hard to
make sure they could be compatible. This usually required having the
lockdep code not be traced. Is it possible to have the same with KMSAN.
That is, have KMSAN not look at anything that lockdep does?

-- Steve