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This can avoid deadlock or stack overflow. But in stack overflow case, it should be OK to increase the recursion depth if needed. So we add a percpu counter in eventfd_ctx to limit the recursion depth for deadlock case. Then it could be fine to increase the global percpu counter later. Signed-off-by: Xie Yongji --- fs/aio.c | 3 ++- fs/eventfd.c | 20 +++++++++++++++++++- include/linux/eventfd.h | 5 +---- 3 files changed, 22 insertions(+), 6 deletions(-) diff --git a/fs/aio.c b/fs/aio.c index 1f32da13d39e..5d82903161f5 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1698,7 +1698,8 @@ static int aio_poll_wake(struct wait_queue_entry *w= ait, unsigned mode, int sync, list_del(&iocb->ki_list); iocb->ki_res.res =3D mangle_poll(mask); req->done =3D true; - if (iocb->ki_eventfd && eventfd_signal_count()) { + if (iocb->ki_eventfd && + eventfd_signal_count(iocb->ki_eventfd)) { iocb =3D NULL; INIT_WORK(&req->work, aio_poll_put_work); schedule_work(&req->work); diff --git a/fs/eventfd.c b/fs/eventfd.c index e265b6dd4f34..2df24f9bada3 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -25,6 +25,8 @@ #include #include =20 +#define EVENTFD_WAKE_DEPTH 0 + DEFINE_PER_CPU(int, eventfd_wake_count); =20 static DEFINE_IDA(eventfd_ida); @@ -42,9 +44,17 @@ struct eventfd_ctx { */ __u64 count; unsigned int flags; + int __percpu *wake_count; int id; }; =20 +bool eventfd_signal_count(struct eventfd_ctx *ctx) +{ + return (this_cpu_read(*ctx->wake_count) || + this_cpu_read(eventfd_wake_count) > EVENTFD_WAKE_DEPTH); +} +EXPORT_SYMBOL_GPL(eventfd_signal_count); + /** * eventfd_signal - Adds @n to the eventfd counter. * @ctx: [in] Pointer to the eventfd context. @@ -71,17 +81,19 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n= ) * it returns true, the eventfd_signal() call should be deferred to a * safe context. */ - if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) + if (WARN_ON_ONCE(eventfd_signal_count(ctx))) return 0; =20 spin_lock_irqsave(&ctx->wqh.lock, flags); this_cpu_inc(eventfd_wake_count); + this_cpu_inc(*ctx->wake_count); if (ULLONG_MAX - ctx->count < n) n =3D ULLONG_MAX - ctx->count; ctx->count +=3D n; if (waitqueue_active(&ctx->wqh)) wake_up_locked_poll(&ctx->wqh, EPOLLIN); this_cpu_dec(eventfd_wake_count); + this_cpu_dec(*ctx->wake_count); spin_unlock_irqrestore(&ctx->wqh.lock, flags); =20 return n; @@ -92,6 +104,7 @@ static void eventfd_free_ctx(struct eventfd_ctx *ctx) { if (ctx->id >=3D 0) ida_simple_remove(&eventfd_ida, ctx->id); + free_percpu(ctx->wake_count); kfree(ctx); } =20 @@ -423,6 +436,11 @@ static int do_eventfd(unsigned int count, int flags) =20 kref_init(&ctx->kref); init_waitqueue_head(&ctx->wqh); + ctx->wake_count =3D alloc_percpu(int); + if (!ctx->wake_count) { + kfree(ctx); + return -ENOMEM; + } ctx->count =3D count; ctx->flags =3D flags; ctx->id =3D ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL); diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index fa0a524baed0..1a11ebbd74a9 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -45,10 +45,7 @@ void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u6= 4 *cnt); =20 DECLARE_PER_CPU(int, eventfd_wake_count); =20 -static inline bool eventfd_signal_count(void) -{ - return this_cpu_read(eventfd_wake_count); -} +bool eventfd_signal_count(struct eventfd_ctx *ctx); =20 #else /* CONFIG_EVENTFD */ =20 --=20 2.11.0