From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-30.mta0.migadu.com [91.218.175.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B0B1502D6A for ; Mon, 28 Sep 2026 22:17:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790633824; cv=none; b=R7+IiVen0gMeNj00d5ojp82prXNBJiuDa9YwvDJDppKcOocj0Bl0ZCXo/gLko/Ji0o5EMTdRv2UeGvUyakKYRHTovxcO4p3b8giAE5pFk4xaqhhjrkqwxgADknPHZLq0tCvT7ACrAX/+WUJtBzX4Mr6p+MVU3Q8jPE0zVAA5M3o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790633824; c=relaxed/simple; bh=MZdoZAnwAB9GP6tC7A/yxqOu30lwP/0wcpM/tqMatbo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rlQXtFxOY2HAc7ZB0BGr+MCC48LHU2exmr+MTQGmW6pDrIyCj76Zrx6XOXHq3ZxFiMS0fHdEu7360ciuKYXvpkqHnxj42ep5l+SNYeM3P30YCTtVdfc3NmixEOpJJRR7AOKYDFh9kzgm033qro6rWjIl0XtuLi0yNaLfnLsFmGE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=mPzj3Oqy; arc=none smtp.client-ip=91.218.175.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="mPzj3Oqy" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=MZdoZAnwAB9GP6tC7A/yxqOu30lwP/0wcpM/tqMatbo=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790633820; v=1; x=1791238620; b=mPzj3OqyOi6Q+sq+7oQrkrleAVCuoxT9FGk+MPNnhQ3KyrL4DjWuQRmF+1CtFGN8SG28ZNwb Vjn/0fuAxXYdyFKWebtcIxIybZDLSmX2mLk+UYv3h6Zi5ielP8nABmKJdJ+BAqHmL10r4MNiLj/ UTS4qTyeW095VtS0/7JAGS68= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 3f08fd830f2b654e; Mon, 28 Sep 2026 22:17:00 +0000 X-Mizu-Trace-ID: 3f08fd830f2b654e X-Migadu-Flow: FLOW_OUT From: Md Haris Iqbal To: Jens Axboe , linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Christoph Hellwig , Keith Busch , Jonathan Corbet , linux-doc@vger.kernel.org, Md Haris Iqbal Subject: [v3 for-next 3/3] Documentation: block: document error injection delay feature Date: Tue, 29 Sep 2026 00:16:34 +0200 Message-ID: <20260928221634.43239-4-haris.iqbal@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260928221634.43239-1-haris.iqbal@linux.dev> References: <20260928221634.43239-1-haris.iqbal@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Document the delay_us option: the delay happens above the driver, a delayed bio is not run through the rules again, and holding a bio back reorders it against bios submitted later. Cc: Christoph Hellwig Assisted-by: Claude:claude-opus-5 Signed-off-by: Md Haris Iqbal --- Documentation/block/error-injection.rst | 39 +++++++++++++++++++++---- 1 file changed, 34 insertions(+), 5 deletions(-) diff --git a/Documentation/block/error-injection.rst b/Documentation/block/error-injection.rst index 81f31af82e65..6f7609b91d24 100644 --- a/Documentation/block/error-injection.rst +++ b/Documentation/block/error-injection.rst @@ -7,9 +7,9 @@ Configurable Error Injection Overview -------- -Configurable error injection allows injecting specific block layer status codes -for sector ranges of a block device. Errors can be injected unconditionally, or -with a given probability. +Configurable error injection allows injecting delays and/or specific block +layer status codes for sector ranges of a block device by adding rules. The +rules can be configured to trigger unconditionally, or with a given probability. To use configurable error injection, CONFIG_BLK_ERROR_INJECTION must be enabled. @@ -34,15 +34,36 @@ op= block layer operation this rule applies to. This uses the XYZ for each REQ_OP_XYZ operation, e.g. READ, WRITE or DISCARD. Mandatory. status= Status to return. This uses XYZ for each BLK_STS_XYZ - code, e.g. IOERR or MEDIUM. Mandatory. + code, e.g. IOERR or MEDIUM. Mandatory unless delay_us + is given. start= First block layer sector the rule applies to. Optional, defaults to 0. nr_sectors= Number of sectors this rule applies. Optional, defaults to the remainder of the device. -chance= Only return a failure with a likelihood of 1/chance. +chance= Only apply the rule with a likelihood of 1/chance. Optional, defaults to 1 (always). +delay_us= Hold the bio back for this many microseconds. Without + status the bio is then submitted to the device as + usual. With status it is failed once the delay has + expired. Bios with REQ_NOWAIT set are never delayed. + Optional, defaults to 0 (no delay). Values above 600 + seconds are rejected. =================== ======================================================= +Delays +------ + +A delayed bio is held above the driver, so the device never sees a slow I/O. +A delay does not reach the blk-mq timeout handler or SCSI error handling. + +A bio that matched a delay rule is not evaluated against the rules again, even +after it is split and resubmitted internally. Removing a rule does not release +bios it is already delaying. + +Holding a bio back reorders it against bios submitted later. On zoned devices +this breaks sequential write ordering and the block layer fails the +out-of-order writes, so only delay reads there. + Example ------- @@ -54,6 +75,14 @@ Return BLK_STS_MEDIUM for every write to /dev/nvme0n1: $ echo 'add,op=WRITE,start=0,status=MEDIUM' > /sys/kernel/debug/block/nvme0n1/error_injection +Delay every read of /dev/nvme0n1 by 10 milliseconds, then issue it normally: + + $ echo 'add,op=READ,delay_us=10000' > /sys/kernel/debug/block/nvme0n1/error_injection + +Fail one in 100 writes with BLK_STS_TIMEOUT, but only after 30 seconds: + + $ echo 'add,op=WRITE,status=TIMEOUT,chance=100,delay_us=30000000' > /sys/kernel/debug/block/nvme0n1/error_injection + Remove all rules for /dev/nvme0n1: $ echo 'removeall' > /sys/kernel/debug/block/nvme0n1/error_injection -- 2.53.0