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Thu, 13 Jul 2023 07:33:06 -0700 (PDT) Date: Thu, 13 Jul 2023 07:33:05 -0700 In-Reply-To: <20230713-vfs-eventfd-signal-v1-2-7fda6c5d212b@kernel.org> Mime-Version: 1.0 References: <20230713-vfs-eventfd-signal-v1-0-7fda6c5d212b@kernel.org> <20230713-vfs-eventfd-signal-v1-2-7fda6c5d212b@kernel.org> Message-ID: Subject: Re: [PATCH 2/2] eventfd: simplify eventfd_signal_mask() From: Sean Christopherson To: Christian Brauner Cc: linux-fsdevel@vger.kernel.org, Vitaly Kuznetsov , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, David Woodhouse , Paul Durrant , Oded Gabbay , Wu Hao , Tom Rix , Moritz Fischer , Xu Yilun , Zhenyu Wang , Zhi Wang , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , Leon Romanovsky , Jason Gunthorpe , Frederic Barrat , Andrew Donnellan , Arnd Bergmann , Greg Kroah-Hartman , Eric Farman , Matthew Rosato , Halil Pasic , Vineeth Vijayan , Peter Oberparleiter , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Tony Krowiak , Jason Herne , Harald Freudenberger , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Diana Craciun , Alex Williamson , Eric Auger , Fei Li , Benjamin LaHaise , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Kirti Wankhede , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fpga@vger.kernel.org, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-usb@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-aio@kvack.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Jens Axboe , Pavel Begunkov , io-uring@vger.kernel.org Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Stat-Signature: ajfz41yayjj15tm1gkqgwm9qmeat545i X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A3D51C0030 X-HE-Tag: 1689258788-282438 X-HE-Meta: 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 85CHbJ7f 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 13, 2023, Christian Brauner wrote: > diff --git a/fs/eventfd.c b/fs/eventfd.c > index dc9e01053235..077be5da72bd 100644 > --- a/fs/eventfd.c > +++ b/fs/eventfd.c > @@ -43,9 +43,10 @@ struct eventfd_ctx { > int id; > }; > > -__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, __poll_t mask) > +bool eventfd_signal_mask(struct eventfd_ctx *ctx, __poll_t mask) > { > unsigned long flags; > + __u64 n = 1; > > /* > * Deadlock or stack overflow issues can happen if we recurse here > @@ -68,7 +69,7 @@ __u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, __poll_t mask) > current->in_eventfd = 0; > spin_unlock_irqrestore(&ctx->wqh.lock, flags); > > - return n; > + return n == 1; > } ... > @@ -58,13 +58,12 @@ static inline struct eventfd_ctx *eventfd_ctx_fdget(int fd) > return ERR_PTR(-ENOSYS); > } > > -static inline int eventfd_signal(struct eventfd_ctx *ctx) > +static inline bool eventfd_signal(struct eventfd_ctx *ctx) > { > return -ENOSYS; > } > > -static inline int eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, > - unsigned mask) > +static inline bool eventfd_signal_mask(struct eventfd_ctx *ctx, unsigned mask) > { > return -ENOSYS; This will morph to "true" for what should be an error case. One option would be to have eventfd_signal_mask() return 0/-errno instead of the count, but looking at all the callers, nothing ever actually consumes the result. KVMGT morphs failure into -EFAULT if (vgpu->msi_trigger && eventfd_signal(vgpu->msi_trigger, 1) != 1) return -EFAULT; but the only caller of that user ignores the return value. if (vgpu_vreg(vgpu, i915_mmio_reg_offset(GEN8_MASTER_IRQ)) & ~GEN8_MASTER_IRQ_CONTROL) inject_virtual_interrupt(vgpu); The sample driver in samples/vfio-mdev/mtty.c uses a similar pattern: prints an error but otherwise ignores the result. So why not return nothing? That will simplify eventfd_signal_mask() a wee bit more, and eliminate that bizarre return value confusion for the ugly stubs, e.g. void eventfd_signal_mask(struct eventfd_ctx *ctx, unsigned mask) { unsigned long flags; /* * Deadlock or stack overflow issues can happen if we recurse here * through waitqueue wakeup handlers. If the caller users potentially * nested waitqueues with custom wakeup handlers, then it should * check eventfd_signal_allowed() before calling this function. If * it returns false, the eventfd_signal() call should be deferred to a * safe context. */ if (WARN_ON_ONCE(current->in_eventfd)) return; spin_lock_irqsave(&ctx->wqh.lock, flags); current->in_eventfd = 1; if (ctx->count < ULLONG_MAX) ctx->count++; if (waitqueue_active(&ctx->wqh)) wake_up_locked_poll(&ctx->wqh, EPOLLIN | mask); current->in_eventfd = 0; spin_unlock_irqrestore(&ctx->wqh.lock, flags); } You could even go further and unify the real and stub versions of eventfd_signal().