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Wed, 14 May 2025 09:42:54 -0700 (PDT) Message-ID: Date: Wed, 14 May 2025 10:42:53 -0600 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] io_uring: move locking inside overflow posting To: Pavel Begunkov , io-uring@vger.kernel.org References: <56fb1f1b3977ae5eec732bd5d39635b69a056b3e.1747209332.git.asml.silence@gmail.com> Content-Language: en-US From: Jens Axboe In-Reply-To: <56fb1f1b3977ae5eec732bd5d39635b69a056b3e.1747209332.git.asml.silence@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/14/25 2:07 AM, Pavel Begunkov wrote: > A preparation patch moving locking protecting the overflow list into > io_cqring_event_overflow(). The locking needs to be conditional because > callers might already hold the lock. It's not the prettiest option, but > it's not much different from the current state. Hopefully, one day we'll > get rid of this nasty locking pattern. > > Signed-off-by: Pavel Begunkov > --- > io_uring/io_uring.c | 53 +++++++++++++++++++++++++++------------------ > 1 file changed, 32 insertions(+), 21 deletions(-) > > diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c > index 068e140b6bd8..5b253e2b6c49 100644 > --- a/io_uring/io_uring.c > +++ b/io_uring/io_uring.c > @@ -718,8 +718,9 @@ static __cold void io_uring_drop_tctx_refs(struct task_struct *task) > } > } > > -static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data, > - s32 res, u32 cflags, u64 extra1, u64 extra2) > +static bool __io_cqring_event_overflow(struct io_ring_ctx *ctx, > + u64 user_data, s32 res, u32 cflags, > + u64 extra1, u64 extra2) > { > struct io_overflow_cqe *ocqe; > size_t ocq_size = sizeof(struct io_overflow_cqe); > @@ -760,6 +761,24 @@ static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data, > return true; > } > > +static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, bool locked, > + u64 user_data, s32 res, u32 cflags, > + u64 extra1, u64 extra2) > +{ > + bool queued; > + > + if (locked) { > + queued = __io_cqring_event_overflow(ctx, user_data, res, cflags, > + extra1, extra2); > + } else { > + spin_lock(&ctx->completion_lock); > + queued = __io_cqring_event_overflow(ctx, user_data, res, cflags, > + extra1, extra2); > + spin_unlock(&ctx->completion_lock); > + } > + return queued; > +} Really not a fan of passing in locking state and having a split helper like that. It's also pretty unwieldy with 7 arguments. Overall, why do we care about atomic vs non-atomic allocations for overflows? If you're hitting overflow, you've messed up... And if it's about cost, gfp atomic alloc will be predictable, vs GFP_KERNEL which can be a lot more involved. -- Jens Axboe