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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::331; envelope-from=philmd@linaro.org; helo=mail-wm1-x331.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi, On 4/12/23 19:57, Stefan Hajnoczi wrote: > On Mon, 4 Dec 2023 at 13:37, Michal Suchánek wrote: >> Looking at tcg.c line 784 is here: >> >> ster_thread(void) >> { >> TCGContext *s = g_malloc(sizeof(*s)); >> unsigned int i, n; >> >> *s = tcg_init_ctx; >> >> /* Relink mem_base. */ >> for (i = 0, n = tcg_init_ctx.nb_globals; i < n; ++i) { >> if (tcg_init_ctx.temps[i].mem_base) { >> ptrdiff_t b = tcg_init_ctx.temps[i].mem_base - tcg_init_ctx.temps; >> tcg_debug_assert(b >= 0 && b < n); >> s->temps[i].mem_base = &s->temps[b]; >> } >> } >> >> /* Claim an entry in tcg_ctxs */ >> n = qatomic_fetch_inc(&tcg_cur_ctxs); >>>>> g_assert(n < tcg_max_ctxs); <<< >> qatomic_set(&tcg_ctxs[n], s); >> >> if (n > 0) { >> alloc_tcg_plugin_context(s); >> tcg_region_initial_alloc(s); >> } >> >> tcg_ctx = s; >> } >> >> Any idea why qemu would be crashing here? > > Hi Michal, > > $ git grep tcg_cur_ctxs > tcg/region.c:409: unsigned int n_ctxs = qatomic_read(&tcg_cur_ctxs); > tcg/region.c:889: unsigned int n_ctxs = qatomic_read(&tcg_cur_ctxs); > tcg/tcg-internal.h:34:extern unsigned int tcg_cur_ctxs; > tcg/tcg.c:241:unsigned int tcg_cur_ctxs; > tcg/tcg.c:806: n = qatomic_fetch_inc(&tcg_cur_ctxs); > tcg/tcg.c:1369: tcg_cur_ctxs = 1; > > I don't see a qatomic_dec(&tcg_cur_ctxs) anywhere, so it seems hot > unplugging a vcpu doesn't release the tcg_cur_ctxs refcount. Do we > need a tcg_unregister_thread() function? Suggested fix posted as RFC patch: https://lore.kernel.org/qemu-devel/20231204194039.56169-1-philmd@linaro.org/