From: "Emilio G. Cota" <cota@braap.org>
To: Robert Foley <robert.foley@linaro.org>
Cc: peter.puhov@linaro.org, alex.bennee@linaro.org, qemu-devel@nongnu.org
Subject: Re: [PATCH 15/19] qht: Fix tsan warnings.
Date: Sat, 23 May 2020 16:44:19 -0400 [thread overview]
Message-ID: <20200523204419.GI382220@sff> (raw)
In-Reply-To: <20200522160755.886-16-robert.foley@linaro.org>
On Fri, May 22, 2020 at 12:07:51 -0400, Robert Foley wrote:
> For example:
> WARNING: ThreadSanitizer: data race (pid=23406)
> Atomic read of size 4 at 0x7b100003e3c8 by thread T7:
> #0 __tsan_atomic32_load <null> (qemu-system-aarch64+0x39a36c)
> #1 qht_do_lookup util/qht.c:495:17 (qemu-system-aarch64+0xd82f7a)
> #2 qht_lookup_custom util/qht.c:539:11 (qemu-system-aarch64+0xd82f7a)
> Previous write of size 8 at 0x7b100003e3c8 by thread T6 (mutexes: write M166769147697783108, write M995435858420506688):
> #0 posix_memalign <null> (qemu-system-aarch64+0x350dd1)
> #1 qemu_try_memalign util/oslib-posix.c:189:11 (qemu-system-aarch64+0xd59317)
> #2 qemu_memalign util/oslib-posix.c:205:27 (qemu-system-aarch64+0xd5943e)
> #3 qht_insert__locked util/qht.c:583:9 (qemu-system-aarch64+0xd837c5)
>
> Signed-off-by: Robert Foley <robert.foley@linaro.org>
> ---
> util/qht.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/util/qht.c b/util/qht.c
> index 67e5d5b916..739a53ced0 100644
> --- a/util/qht.c
> +++ b/util/qht.c
> @@ -69,6 +69,7 @@
> #include "qemu/qht.h"
> #include "qemu/atomic.h"
> #include "qemu/rcu.h"
> +#include "qemu/tsan.h"
>
> //#define QHT_DEBUG
>
> @@ -580,10 +581,12 @@ static void *qht_insert__locked(const struct qht *ht, struct qht_map *map,
> b = b->next;
> } while (b);
>
> + TSAN_ANNOTATE_IGNORE_WRITES_BEGIN();
> b = qemu_memalign(QHT_BUCKET_ALIGN, sizeof(*b));
> memset(b, 0, sizeof(*b));
> new = b;
> i = 0;
> + TSAN_ANNOTATE_IGNORE_WRITES_END();
I cannot reproduce this warning post-series with detect_deadlocks=0
but my hypothesis is that this is a side effect of tsan not understanding
the seqlock: tsan sees that below we "publish" this piece of memory with
an atomic write (in atomic_rcu_set), and does not see that with
seqlock_write_begin we have a write memory barrier. I wonder if
what we need instead is to annotate the seqlock functions, not the
callers.
Thanks,
E.
next prev parent reply other threads:[~2020-05-23 20:45 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-22 16:07 [PATCH 00/19] Add Thread Sanitizer support to QEMU Robert Foley
2020-05-22 16:07 ` [PATCH 01/19] configure: add --enable-tsan flag + fiber annotations for coroutine-ucontext Robert Foley
2020-05-23 16:55 ` Philippe Mathieu-Daudé
2020-05-26 12:38 ` Robert Foley
2020-06-17 14:24 ` Stefan Hajnoczi
2020-06-17 15:56 ` Alex Bennée
2020-06-17 21:27 ` Robert Foley
2020-05-22 16:07 ` [PATCH 02/19] cpu: convert queued work to a QSIMPLEQ Robert Foley
2020-05-24 10:20 ` Philippe Mathieu-Daudé
2020-05-26 15:01 ` Robert Foley
2020-05-22 16:07 ` [PATCH 03/19] thread: add qemu_spin_destroy Robert Foley
2020-05-22 16:07 ` [PATCH 04/19] cputlb: destroy CPUTLB with tlb_destroy Robert Foley
2020-05-22 16:07 ` [PATCH 05/19] qht: call qemu_spin_destroy for head buckets Robert Foley
2020-05-22 16:07 ` [PATCH 06/19] tcg: call qemu_spin_destroy for tb->jmp_lock Robert Foley
2020-05-22 16:07 ` [PATCH 07/19] translate-all: call qemu_spin_destroy for PageDesc Robert Foley
2020-05-22 16:07 ` [PATCH 08/19] thread: add tsan annotations to QemuSpin Robert Foley
2020-05-22 16:07 ` [PATCH 09/19] tests/docker: Added docker build support for TSan Robert Foley
2020-05-22 16:07 ` [PATCH 10/19] include/qemu: Added tsan.h for annotations Robert Foley
2020-05-23 17:20 ` Emilio G. Cota
2020-05-23 21:37 ` Emilio G. Cota
2020-05-22 16:07 ` [PATCH 11/19] accel/tcg: Fixed tsan warnings related to parallel_cpus Robert Foley
2020-05-23 17:21 ` Emilio G. Cota
2020-05-22 16:07 ` [PATCH 12/19] configure: added tsan support for blacklist Robert Foley
2020-05-23 17:27 ` Emilio G. Cota
2020-05-26 14:07 ` Robert Foley
2020-05-22 16:07 ` [PATCH 13/19] accel/tcg: Fixed tsan warnings Robert Foley
2020-05-23 20:06 ` Emilio G. Cota
2020-05-26 15:14 ` Robert Foley
2020-05-26 18:47 ` Paolo Bonzini
2020-05-22 16:07 ` [PATCH 14/19] util/async: " Robert Foley
2020-05-23 20:12 ` Emilio G. Cota
2020-05-26 15:19 ` Robert Foley
2020-05-26 10:32 ` Stefan Hajnoczi
2020-05-26 15:21 ` Robert Foley
2020-05-22 16:07 ` [PATCH 15/19] qht: Fix " Robert Foley
2020-05-23 20:44 ` Emilio G. Cota [this message]
2020-05-22 16:07 ` [PATCH 16/19] util: fixed tsan warnings in thread_pool.c Robert Foley
2020-05-26 20:18 ` Paolo Bonzini
2020-05-22 16:07 ` [PATCH 17/19] util: Added tsan annotate for thread name Robert Foley
2020-05-23 20:29 ` Emilio G. Cota
2020-05-22 16:07 ` [PATCH 18/19] target/arm: Fix tsan warning in cpu.c Robert Foley
2020-05-22 17:44 ` Peter Maydell
2020-05-22 21:33 ` Robert Foley
2020-05-22 22:36 ` Peter Maydell
2020-05-23 17:18 ` Emilio G. Cota
2020-05-26 14:01 ` Robert Foley
2020-05-22 16:07 ` [PATCH 19/19] docs: Added details on TSan to testing.rst Robert Foley
2020-05-23 20:29 ` Emilio G. Cota
2020-05-22 21:07 ` [PATCH 00/19] Add Thread Sanitizer support to QEMU no-reply
2020-05-23 21:36 ` Emilio G. Cota
2020-05-26 15:18 ` Robert Foley
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