mirrors/qemu
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

qom: convert the CPU list to RCU

Browse Source 
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
cpus-common.c
View File

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

11
include/qom/cpu.h
View File

@ -26,6 +26,7 @@
#include "exec/memattrs.h" #include "exec/memattrs.h"
#include "qapi/qapi-types-run-state.h" #include "qapi/qapi-types-run-state.h"
#include "qemu/bitmap.h" #include "qemu/bitmap.h"
#include "qemu/rcu_queue.h"
#include "qemu/queue.h" #include "qemu/queue.h"
#include "qemu/thread.h" #include "qemu/thread.h"
@ -442,13 +443,11 @@ struct CPUState {
QTAILQ_HEAD(CPUTailQ, CPUState); QTAILQ_HEAD(CPUTailQ, CPUState);
extern struct CPUTailQ cpus; extern struct CPUTailQ cpus;
#define CPU_NEXT(cpu) QTAILQ_NEXT(cpu, node) #define first_cpu QTAILQ_FIRST_RCU(&cpus)
#define CPU_FOREACH(cpu) QTAILQ_FOREACH(cpu, &cpus, node) #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) \ #define CPU_FOREACH_SAFE(cpu, next_cpu) \
QTAILQ_FOREACH_SAFE(cpu, &cpus, node, next_cpu) QTAILQ_FOREACH_SAFE_RCU(cpu, &cpus, node, next_cpu)
#define CPU_FOREACH_REVERSE(cpu) \
QTAILQ_FOREACH_REVERSE(cpu, &cpus, CPUTailQ, node)
#define first_cpu QTAILQ_FIRST(&cpus)
extern __thread CPUState *current_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. */ Discard information about the parent threads. */
CPU_FOREACH_SAFE(cpu, next_cpu) { CPU_FOREACH_SAFE(cpu, next_cpu) {
if (cpu != thread_cpu) { if (cpu != thread_cpu) {
QTAILQ_REMOVE(&cpus, cpu, node); QTAILQ_REMOVE_RCU(&cpus, cpu, node);
} }
} }
qemu_init_cpu_list(); 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; TaskState *ts;
/* Remove the CPU from the list. */ /* Remove the CPU from the list. */
QTAILQ_REMOVE(&cpus, cpu, node); QTAILQ_REMOVE_RCU(&cpus, cpu, node);
cpu_list_unlock(); 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); const S390CPUDef *def = s390_find_cpu_def(type, gen, ec_ga, NULL);
g_assert(def); 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 /* TCG emulates some features that can usually not be enabled with
* the emulated machine generation. Make sure they can be enabled * the emulated machine generation. Make sure they can be enabled