From: Marco Elver <elver@google.com> To: Alan Stern <stern@rowland.harvard.edu> Cc: Linus Torvalds <torvalds@linux-foundation.org>, Eric Dumazet <edumazet@google.com>, Alexei Starovoitov <alexei.starovoitov@gmail.com>, Eric Dumazet <eric.dumazet@gmail.com>, syzbot <syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, syzkaller-bugs <syzkaller-bugs@googlegroups.com>, Al Viro <viro@zeniv.linux.org.uk>, Andrea Parri <parri.andrea@gmail.com>, "Paul E. McKenney" <paulmck@kernel.org>, LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com> Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file Date: Wed, 13 Nov 2019 23:48:08 +0100 Message-ID: <20191113224808.GA3960@google.com> (raw) In-Reply-To: <Pine.LNX.4.44L0.1911131648010.1558-100000@iolanthe.rowland.org> On Wed, 13 Nov 2019, Alan Stern wrote: > On Wed, 13 Nov 2019, Marco Elver wrote: > > > An expression works fine. The below patch would work with KCSAN, and all > > your above examples work. > > > > Re name: would it make sense to more directly convey the intent? I.e. > > "this expression can race, and it's fine that the result is approximate > > if it does"? > > > > My vote would go to something like 'smp_lossy' or 'lossy_race' -- but > > don't have a strong preference, and would also be fine with 'data_race'. > > Whatever is most legible. Comments? > > Lossiness isn't really relevant. Things like sticky writes work > perfectly well with data races; they don't lose anything. > > My preference would be for "data_race" or something very similar > ("racy"? "race_ok"?). That's the whole point -- we know the > operation can be part of a data race and we don't care. Makes sense. Let's stick with 'data_race' then. As Linus pointed out this won't yet work for void types and if-statements. How frequent would that use be? Should it even be encouraged? I'll add this as a patch for the next version of the KCSAN patch series. Thanks, -- Marco diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 0b6506b9dd11..a97f323b61e3 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -308,6 +308,26 @@ unsigned long read_word_at_a_time(const void *addr) __u.__val; \ }) +#include <linux/kcsan.h> + +/* + * data_race: macro to document that accesses in an expression may conflict with + * other concurrent accesses resulting in data races, but the resulting + * behaviour is deemed safe regardless. + * + * This macro *does not* affect normal code generation, but is a hint to tooling + * that data races here are intentional. + */ +#define data_race(expr) \ + ({ \ + typeof(({ expr; })) __val; \ + kcsan_nestable_atomic_begin(); \ + __val = ({ expr; }); \ + kcsan_nestable_atomic_end(); \ + __val; \ + }) +#else + #endif /* __KERNEL__ */ /*
next prev parent reply index Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <CAHk-=wjB61GNmqpX0BLA5tpL4tsjWV7akaTc2Roth7uGgax+mw@mail.gmail.com> 2019-11-10 16:09 ` Alan Stern 2019-11-10 19:10 ` Marco Elver 2019-11-11 15:51 ` Alan Stern 2019-11-11 16:51 ` Linus Torvalds 2019-11-11 17:52 ` Eric Dumazet 2019-11-11 18:04 ` Linus Torvalds 2019-11-11 18:31 ` Eric Dumazet 2019-11-11 18:44 ` Eric Dumazet 2019-11-11 19:00 ` Linus Torvalds 2019-11-11 19:13 ` Eric Dumazet 2019-11-11 20:43 ` Linus Torvalds 2019-11-11 20:46 ` Linus Torvalds 2019-11-11 21:53 ` Eric Dumazet 2019-11-11 23:51 ` Linus Torvalds 2019-11-12 16:50 ` Kirill Smelkov 2019-11-12 17:23 ` Linus Torvalds 2019-11-12 17:36 ` Linus Torvalds 2019-11-17 18:56 ` Kirill Smelkov 2019-11-17 19:20 ` Linus Torvalds 2019-11-11 18:50 ` Linus Torvalds 2019-11-11 18:59 ` Marco Elver 2019-11-11 18:59 ` Eric Dumazet 2019-11-10 19:12 ` Linus Torvalds 2019-11-10 19:20 ` Linus Torvalds 2019-11-10 20:44 ` Paul E. McKenney 2019-11-10 21:10 ` Linus Torvalds 2019-11-10 21:31 ` Paul E. McKenney 2019-11-11 14:17 ` Marco Elver 2019-11-11 14:31 ` Paul E. McKenney 2019-11-11 15:10 ` Marco Elver 2019-11-13 0:25 ` Paul E. McKenney 2019-11-12 19:14 ` Alan Stern 2019-11-12 19:47 ` Linus Torvalds 2019-11-12 20:29 ` Alan Stern 2019-11-12 20:58 ` Linus Torvalds 2019-11-12 21:13 ` Linus Torvalds 2019-11-12 22:05 ` Marco Elver 2019-11-12 21:48 ` Alan Stern 2019-11-12 22:07 ` Eric Dumazet 2019-11-12 22:44 ` Alexei Starovoitov 2019-11-12 23:17 ` Eric Dumazet 2019-11-12 23:40 ` Linus Torvalds 2019-11-13 15:00 ` Marco Elver 2019-11-13 16:57 ` Linus Torvalds 2019-11-13 21:33 ` Marco Elver 2019-11-13 21:50 ` Alan Stern 2019-11-13 22:48 ` Marco Elver [this message] 2019-11-08 13:16 syzbot 2019-11-08 13:28 ` Eric Dumazet 2019-11-08 17:01 ` Linus Torvalds 2019-11-08 17:22 ` Eric Dumazet 2019-11-08 17:38 ` Linus Torvalds 2019-11-08 17:53 ` Eric Dumazet 2019-11-08 17:55 ` Eric Dumazet 2019-11-08 18:02 ` Eric Dumazet 2019-11-08 18:12 ` Linus Torvalds 2019-11-08 20:30 ` Linus Torvalds 2019-11-08 20:53 ` Eric Dumazet 2019-11-08 21:36 ` Linus Torvalds 2019-11-08 18:05 ` Linus Torvalds 2019-11-08 18:15 ` Marco Elver 2019-11-08 18:40 ` Linus Torvalds 2019-11-08 19:48 ` Marco Elver 2019-11-08 20:26 ` Linus Torvalds 2019-11-08 21:57 ` Alan Stern 2019-11-08 22:06 ` Linus Torvalds 2019-11-09 23:08 ` Alan Stern
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