Jason Wang
2021-Jan-20 04:24 UTC
[RFC v3 01/11] eventfd: track eventfd_signal() recursion depth separately in different cases
On 2021/1/19 ??12:59, Xie Yongji wrote:> Now we have a global percpu counter to limit the recursion depth > of eventfd_signal(). 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.I wonder whether or not it's worth to introduce percpu for each eventfd. How about simply check if eventfd_signal_count() is greater than 2? Thanks> > Signed-off-by: Xie Yongji <xieyongji at bytedance.com> > --- > 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 *wait, unsigned mode, int sync, > list_del(&iocb->ki_list); > iocb->ki_res.res = mangle_poll(mask); > req->done = true; > - if (iocb->ki_eventfd && eventfd_signal_count()) { > + if (iocb->ki_eventfd && > + eventfd_signal_count(iocb->ki_eventfd)) { > iocb = 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 <linux/idr.h> > #include <linux/uio.h> > > +#define EVENTFD_WAKE_DEPTH 0 > + > DEFINE_PER_CPU(int, eventfd_wake_count); > > static DEFINE_IDA(eventfd_ida); > @@ -42,9 +44,17 @@ struct eventfd_ctx { > */ > __u64 count; > unsigned int flags; > + int __percpu *wake_count; > int id; > }; > > +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; > > 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 = ULLONG_MAX - ctx->count; > ctx->count += 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); > > return n; > @@ -92,6 +104,7 @@ static void eventfd_free_ctx(struct eventfd_ctx *ctx) > { > if (ctx->id >= 0) > ida_simple_remove(&eventfd_ida, ctx->id); > + free_percpu(ctx->wake_count); > kfree(ctx); > } > > @@ -423,6 +436,11 @@ static int do_eventfd(unsigned int count, int flags) > > kref_init(&ctx->kref); > init_waitqueue_head(&ctx->wqh); > + ctx->wake_count = alloc_percpu(int); > + if (!ctx->wake_count) { > + kfree(ctx); > + return -ENOMEM; > + } > ctx->count = count; > ctx->flags = flags; > ctx->id = 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, __u64 *cnt); > > DECLARE_PER_CPU(int, eventfd_wake_count); > > -static inline bool eventfd_signal_count(void) > -{ > - return this_cpu_read(eventfd_wake_count); > -} > +bool eventfd_signal_count(struct eventfd_ctx *ctx); > > #else /* CONFIG_EVENTFD */ >