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qom: convert the CPU list to RCU 

Iterating over the list without using atomics is undefined behaviour,
since the list can be modified concurrently by other threads (e.g.
every time a new thread is created in user-mode).

Fix it by implementing the CPU list as an RCU QTAILQ. This requires
a little bit of extra work to traverse list in reverse order (see
previous patch), but other than that the conversion is trivial.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20180819091335.22863-12-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Emilio G. Cota 2018-08-19 05:13:35 -04:00 committed by Paolo Bonzini
parent 04d595b300
commit 068a5ea02f
6 changed files with 11 additions and 12 deletions
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4
cpus-common.c
View File

@ -84,7 +84,7 @@ void cpu_list_add(CPUState *cpu)
} else {
assert(!cpu_index_auto_assigned);
}
QTAILQ_INSERT_TAIL(&cpus, cpu, node);
QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
qemu_mutex_unlock(&qemu_cpu_list_lock);
finish_safe_work(cpu);
@ -101,7 +101,7 @@ void cpu_list_remove(CPUState *cpu)
assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus, CPUTailQ)));
QTAILQ_REMOVE(&cpus, cpu, node);
QTAILQ_REMOVE_RCU(&cpus, cpu, node);
cpu->cpu_index = UNASSIGNED_CPU_INDEX;
qemu_mutex_unlock(&qemu_cpu_list_lock);
}

2
cpus.c
View File

@ -1491,7 +1491,7 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
atomic_mb_set(&cpu->exit_request, 0);
}
qemu_tcg_rr_wait_io_event(cpu ? cpu : QTAILQ_FIRST(&cpus));
qemu_tcg_rr_wait_io_event(cpu ? cpu : first_cpu);
deal_with_unplugged_cpus();
}

11
include/qom/cpu.h
View File

@ -26,6 +26,7 @@
#include "exec/memattrs.h"
#include "qapi/qapi-types-run-state.h"
#include "qemu/bitmap.h"
#include "qemu/rcu_queue.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
@ -442,13 +443,11 @@ struct CPUState {
QTAILQ_HEAD(CPUTailQ, CPUState);
extern struct CPUTailQ cpus;
#define CPU_NEXT(cpu) QTAILQ_NEXT(cpu, node)
#define CPU_FOREACH(cpu) QTAILQ_FOREACH(cpu, &cpus, node)
#define first_cpu QTAILQ_FIRST_RCU(&cpus)
#define CPU_NEXT(cpu) QTAILQ_NEXT_RCU(cpu, node)
#define CPU_FOREACH(cpu) QTAILQ_FOREACH_RCU(cpu, &cpus, node)
#define CPU_FOREACH_SAFE(cpu, next_cpu) \
QTAILQ_FOREACH_SAFE(cpu, &cpus, node, next_cpu)
#define CPU_FOREACH_REVERSE(cpu) \
QTAILQ_FOREACH_REVERSE(cpu, &cpus, CPUTailQ, node)
#define first_cpu QTAILQ_FIRST(&cpus)
QTAILQ_FOREACH_SAFE_RCU(cpu, &cpus, node, next_cpu)
extern __thread CPUState *current_cpu;

2
linux-user/main.c
View File

@ -126,7 +126,7 @@ void fork_end(int child)
Discard information about the parent threads. */
CPU_FOREACH_SAFE(cpu, next_cpu) {
if (cpu != thread_cpu) {
QTAILQ_REMOVE(&cpus, cpu, node);
QTAILQ_REMOVE_RCU(&cpus, cpu, node);
}
}
qemu_init_cpu_list();

2
linux-user/syscall.c
View File

@ -8157,7 +8157,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
TaskState *ts;
/* Remove the CPU from the list. */
QTAILQ_REMOVE(&cpus, cpu, node);
QTAILQ_REMOVE_RCU(&cpus, cpu, node);
cpu_list_unlock();

2
target/s390x/cpu_models.c
View File

@ -1096,7 +1096,7 @@ void s390_set_qemu_cpu_model(uint16_t type, uint8_t gen, uint8_t ec_ga,
const S390CPUDef *def = s390_find_cpu_def(type, gen, ec_ga, NULL);
g_assert(def);
g_assert(QTAILQ_EMPTY(&cpus));
g_assert(QTAILQ_EMPTY_RCU(&cpus));
/* TCG emulates some features that can usually not be enabled with
* the emulated machine generation. Make sure they can be enabled