From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52195) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cfyQX-0003Lx-SP for qemu-devel@nongnu.org; Mon, 20 Feb 2017 19:35:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cfyQT-0005oz-VO for qemu-devel@nongnu.org; Mon, 20 Feb 2017 19:35:33 -0500 Received: from mail-wr0-x230.google.com ([2a00:1450:400c:c0c::230]:35028) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cfyQT-0005om-Ly for qemu-devel@nongnu.org; Mon, 20 Feb 2017 19:35:29 -0500 Received: by mail-wr0-x230.google.com with SMTP id s27so26278030wrb.2 for ; Mon, 20 Feb 2017 16:35:29 -0800 (PST) References: <20170220145335.591-1-bobby.prani@gmail.com> <87fuj8x2gi.fsf@linaro.org> <87k28ko1qw.fsf@gmail.com> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <87k28ko1qw.fsf@gmail.com> Date: Tue, 21 Feb 2017 00:35:33 +0000 Message-ID: <87d1ecwfca.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] mttcg: Set jmp_env to handle exit from tb_gen_code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pranith Kumar Cc: qemu-devel@nongnu.org, rth@twiddle.net Pranith Kumar writes: > Alex Bennée writes: > >> Pranith Kumar writes: >> >>> tb_gen_code() can exit execution using cpu_exit_loop() when it cannot >>> allocate new tb's. To handle this, we need to properly set the jmp_env >>> pointer ahead of calling tb_gen_code(). >>> >>> CC:Alex Bennée >>> CC: Richard Henderson >>> Signed-off-by: Pranith Kumar >>> --- >>> cpu-exec.c | 23 +++++++++++------------ >>> 1 file changed, 11 insertions(+), 12 deletions(-) >>> >>> diff --git a/cpu-exec.c b/cpu-exec.c >>> index 97d79612d9..4b70988b24 100644 >>> --- a/cpu-exec.c >>> +++ b/cpu-exec.c >>> @@ -236,23 +236,22 @@ static void cpu_exec_step(CPUState *cpu) >>> >>> cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags); >>> tb_lock(); >>> - tb = tb_gen_code(cpu, pc, cs_base, flags, >>> - 1 | CF_NOCACHE | CF_IGNORE_ICOUNT); >>> - tb->orig_tb = NULL; >>> - tb_unlock(); >>> - >>> - cc->cpu_exec_enter(cpu); >>> - >> >> It occurs to me we are also diverging in our locking pattern from >> tb_find which takes mmap_lock first. This is a NOP for system emulation >> but needed for user-emulation (for which we can do cpu_exec_step but not >> cpu_exec_nocache). > > Right. So we have to take the mmap_lock() before calling > tb_gen_code(). However, this lock is released in the error path before calling > cpu_loop_exit() if allocation of a new tb fails. The following is what I have > after merging with the previous EXCP_ATOMIC handling patch. Hmm we are a start/end_exclusive() though so what could we be racing against that also wants the mmap_lock()? Could it be held by anything at this point as every user needs to be woken up? > > diff --git a/cpu-exec.c b/cpu-exec.c > index a8e04bffbf..2bb3ba3672 100644 > --- a/cpu-exec.c > +++ b/cpu-exec.c > @@ -228,6 +228,7 @@ static void cpu_exec_nocache(CPUState *cpu, int max_cycles, > > static void cpu_exec_step(CPUState *cpu) > { > + CPUClass *cc = CPU_GET_CLASS(cpu); > CPUArchState *env = (CPUArchState *)cpu->env_ptr; > TranslationBlock *tb; > target_ulong cs_base, pc; > @@ -235,16 +236,24 @@ static void cpu_exec_step(CPUState *cpu) > > cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags); > tb_lock(); > - tb = tb_gen_code(cpu, pc, cs_base, flags, > - 1 | CF_NOCACHE | CF_IGNORE_ICOUNT); > - tb->orig_tb = NULL; > - tb_unlock(); > - /* execute the generated code */ > - trace_exec_tb_nocache(tb, pc); > - cpu_tb_exec(cpu, tb); > - tb_lock(); > - tb_phys_invalidate(tb, -1); > - tb_free(tb); > + if (sigsetjmp(cpu->jmp_env, 0) == 0) { > + mmap_lock(); > + tb = tb_gen_code(cpu, pc, cs_base, flags, > + 1 | CF_NOCACHE | CF_IGNORE_ICOUNT); > + tb->orig_tb = NULL; > + mmap_unlock(); > + tb_unlock(); > + > + cc->cpu_exec_enter(cpu); > + /* execute the generated code */ > + trace_exec_tb_nocache(tb, pc); > + cpu_tb_exec(cpu, tb); > + cc->cpu_exec_exit(cpu); > + > + tb_lock(); > + tb_phys_invalidate(tb, -1); > + tb_free(tb); > + } > tb_unlock(); > } > > diff --git a/cpus.c b/cpus.c > index 77bba08f9a..b39408b4b1 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -1347,6 +1347,11 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg) > if (r == EXCP_DEBUG) { > cpu_handle_guest_debug(cpu); > break; > + } else if (r == EXCP_ATOMIC) { > + qemu_mutex_unlock_iothread(); > + cpu_exec_step_atomic(cpu); > + qemu_mutex_lock_iothread(); > + break; > } > } else if (cpu->stop) { > if (cpu->unplug) { > @@ -1457,6 +1462,10 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) > */ > g_assert(cpu->halted); > break; > + case EXCP_ATOMIC: > + qemu_mutex_unlock_iothread(); > + cpu_exec_step_atomic(cpu); > + qemu_mutex_lock_iothread(); > default: > /* Ignore everything else? */ > break; -- Alex Bennée