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Mon, 13 Oct 2025 09:26:22 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGIn5vNuVZ0CPukcmdqUy65P6SXHfg31+sAMl7HbkAmAxfF0SCFDMh2VHDcOvMtTOQ9fDZZsw== X-Received: by 2002:a05:6000:41d1:b0:403:6f7d:ac5d with SMTP id ffacd0b85a97d-4266e7dfaf4mr12192598f8f.34.1760372782313; Mon, 13 Oct 2025 09:26:22 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, qemu-stable@nongnu.org Subject: [PATCH] async: access bottom half flags with qatomic_read Date: Mon, 13 Oct 2025 18:26:20 +0200 Message-ID: <20251013162620.995747-1-pbonzini@redhat.com> X-Mailer: git-send-email 2.51.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1760372838758158500 Content-Type: text/plain; charset="utf-8" Running test-aio-multithread under TSAN reveals data races on bh->flags. Because bottom halves may be scheduled or canceled asynchronously, without taking a lock, adjust aio_compute_bh_timeout() and aio_ctx_check() to use a relaxed read to access the flags. Use an acquire load to ensure that anything that was written prior to qemu_bh_schedule() is visible. Resolves: #2749 Resolves: #851 Cc: qemu-stable@nongnu.org Signed-off-by: Paolo Bonzini Reviewed-by: Philippe Mathieu-Daud=C3=A9 --- util/async.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/util/async.c b/util/async.c index 2719c629ae9..a736d2cd0d0 100644 --- a/util/async.c +++ b/util/async.c @@ -256,8 +256,9 @@ static int64_t aio_compute_bh_timeout(BHList *head, int= timeout) QEMUBH *bh; =20 QSLIST_FOREACH_RCU(bh, head, next) { - if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDULED)= { - if (bh->flags & BH_IDLE) { + int flags =3D qatomic_load_acquire(&bh->flags); + if ((flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDULED) { + if (flags & BH_IDLE) { /* idle bottom halves will be polled at least * every 10ms */ timeout =3D 10000000; @@ -335,14 +336,16 @@ aio_ctx_check(GSource *source) aio_notify_accept(ctx); =20 QSLIST_FOREACH_RCU(bh, &ctx->bh_list, next) { - if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDULED)= { + int flags =3D qatomic_load_acquire(&bh->flags); + if ((flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDULED) { return true; } } =20 QSIMPLEQ_FOREACH(s, &ctx->bh_slice_list, next) { QSLIST_FOREACH_RCU(bh, &s->bh_list, next) { - if ((bh->flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDU= LED) { + int flags =3D qatomic_load_acquire(&bh->flags); + if ((flags & (BH_SCHEDULED | BH_DELETED)) =3D=3D BH_SCHEDULED)= { return true; } } --=20 2.51.0