From patchwork Mon Feb 10 11:40:39 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oleg Nesterov X-Patchwork-Id: 13967737 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D72D1E570A for ; Mon, 10 Feb 2025 11:41:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739187682; cv=none; b=XaYnsUOHwSmkPP6Frp2gpjWvdi8pkA0UeLz/+Yx+KKDm//RqAv7LLJrdfoz1p70JwihkXsYJ/xdp1Kffb0CxUuIdZefYmbMaKTAb/URK5jsGapy9rY7EFlXTq7lVJDBVsk5/aU0+HSlKpp2xBMCkHAf1OWajGQbo8pfeh8LPM5s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739187682; c=relaxed/simple; bh=A0Z5p7jAtcJP+bUxNWQBTn+qyqsJKGT8czafy7DAnfs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VWVxnvbBCwDcY5iaMBfEtpIqrkaKtHuWDRM023zdmXlNdx0Ao5oHXtB29aYBqS+9+lrS/m2OV7sBjil7DZPfX1CAipUDf08Jhu/j3idSu0cfZZHeUh8aNY9LugAWYQcf1L3JbbFUtwW9kNK9wCKJeSyTqz3z24AsSCqfqU5tIMw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=iKQIp2uw; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="iKQIp2uw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739187679; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ClbELSS8AwfbHSwnhY5LOEfcBwAX2tRaVpjOvrMpwf0=; b=iKQIp2uwo8GW9C9N2dIsQFkVeVulyvj5b01DSvYUwGyACyNqHWPE0j2nEogrLWyqpDKHRb EzEMvl/Z7hPs5EcN6GaBlcNiNZJ5+ay1BMi2HZtA2dXylXP2BuYejk/bzznTjrlNwghB9f Gyc3awx/krqsm3GPN6ScVH2FYTf9ty0= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-682-Qa8SLWEQPIG-s5zBQCTFAw-1; Mon, 10 Feb 2025 06:41:14 -0500 X-MC-Unique: Qa8SLWEQPIG-s5zBQCTFAw-1 X-Mimecast-MFC-AGG-ID: Qa8SLWEQPIG-s5zBQCTFAw Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D3E6F1955DB8; Mon, 10 Feb 2025 11:41:11 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.113]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 383721800570; Mon, 10 Feb 2025 11:41:06 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 10 Feb 2025 12:40:45 +0100 (CET) Date: Mon, 10 Feb 2025 12:40:39 +0100 From: Oleg Nesterov To: Christian Brauner , Jeff Layton , Linus Torvalds Cc: David Howells , "Gautham R. Shenoy" , K Prateek Nayak , Mateusz Guzik , Neeraj Upadhyay , Oliver Sang , Swapnil Sapkal , WangYuli , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/1] pipe: change pipe_write() to never add a zero-sized buffer Message-ID: <20250210114039.GA3588@redhat.com> References: <20250209150718.GA17013@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20250209150718.GA17013@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to preallocate slot") changed pipe_write() to increment pipe->head in advance. IIUC to avoid the race with the post_one_notification()-like code which can add another buffer under pipe->rd_wait.lock without pipe->mutex. This is no longer necessary after c73be61cede5 ("pipe: Add general notification queue support"), pipe_write() checks pipe_has_watch_queue() and returns -EXDEV at the start. And can't help in any case, pipe_write() no longer takes this rd_wait.lock spinlock. Change pipe_write() to call copy_page_from_iter() first and do nothing if it fails. This way pipe_write() can't add a zero-sized buffer and we can simplify pipe_read() which currently has to take care of this very unlikely case. Also, with this patch we can probably kill eat_empty_buffer() and more "is this buffer empty" checks in fs/splice.c later. Link: https://lore.kernel.org/all/20250209150718.GA17013@redhat.com/ Signed-off-by: Oleg Nesterov Tested-by: K Prateek Nayak --- fs/pipe.c | 45 +++++++++------------------------------------ 1 file changed, 9 insertions(+), 36 deletions(-) diff --git a/fs/pipe.c b/fs/pipe.c index 2ae75adfba64..b0641f75b1ba 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -360,29 +360,9 @@ anon_pipe_read(struct kiocb *iocb, struct iov_iter *to) break; } mutex_unlock(&pipe->mutex); - /* * We only get here if we didn't actually read anything. * - * However, we could have seen (and removed) a zero-sized - * pipe buffer, and might have made space in the buffers - * that way. - * - * You can't make zero-sized pipe buffers by doing an empty - * write (not even in packet mode), but they can happen if - * the writer gets an EFAULT when trying to fill a buffer - * that already got allocated and inserted in the buffer - * array. - * - * So we still need to wake up any pending writers in the - * _very_ unlikely case that the pipe was full, but we got - * no data. - */ - if (unlikely(wake_writer)) - wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM); - kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); - - /* * But because we didn't read anything, at this point we can * just return directly with -ERESTARTSYS if we're interrupted, * since we've done any required wakeups and there's no need @@ -391,7 +371,6 @@ anon_pipe_read(struct kiocb *iocb, struct iov_iter *to) if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0) return -ERESTARTSYS; - wake_writer = false; wake_next_reader = true; mutex_lock(&pipe->mutex); } @@ -526,33 +505,27 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from) pipe->tmp_page = page; } - /* Allocate a slot in the ring in advance and attach an - * empty buffer. If we fault or otherwise fail to use - * it, either the reader will consume it or it'll still - * be there for the next write. - */ - pipe->head = head + 1; + copied = copy_page_from_iter(page, 0, PAGE_SIZE, from); + if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) { + if (!ret) + ret = -EFAULT; + break; + } + pipe->head = head + 1; + pipe->tmp_page = NULL; /* Insert it into the buffer array */ buf = &pipe->bufs[head & mask]; buf->page = page; buf->ops = &anon_pipe_buf_ops; buf->offset = 0; - buf->len = 0; if (is_packetized(filp)) buf->flags = PIPE_BUF_FLAG_PACKET; else buf->flags = PIPE_BUF_FLAG_CAN_MERGE; - pipe->tmp_page = NULL; - copied = copy_page_from_iter(page, 0, PAGE_SIZE, from); - if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) { - if (!ret) - ret = -EFAULT; - break; - } - ret += copied; buf->len = copied; + ret += copied; if (!iov_iter_count(from)) break;