From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 5BEA33DBD7C; Thu, 9 Apr 2026 16:03:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775750586; cv=none; b=bwTFkFet96OKQezBdz+1c75SJD4Lxz/pZg3984jKxDXz6VFZ2uOgKRFpzwuLpuS4HxXqEVWPsLKOrXYAc0/5yRm72w4cmvtNWN0WQi4ykVrsSufL9bdgfVsQhinO3yKt1G7GNamS1MYDmrMnTI1ToHWycDPw8NkIOaBs86TikS0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775750586; c=relaxed/simple; bh=8C+YvCVnj1h+qaRDw3us46NBjE4kdCB2TRbrr+Hct5w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Hhx7PnZ69sLlFwT3AyIuYi+wxnBrUgJysz4IC3hefebp2WKQH8dREfBugRZRxBSAr7M5DhjOBdvrdADiW0ekYslAr2yNb9iy3Y6o35htg2Qk7CMtOOvtW6dnw80GgSX3tX9H/fr26O+8CEHcLk9FO9Q5fpzVQbnzQxQQ2cEXgBc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=lst.de; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Gh85pBMa; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Gh85pBMa" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description; bh=h53OigJvhKi2R7WTc8tD2Nme4RfoPqZlyMjNikVjZqA=; b=Gh85pBMata1NecuSQtkzPmgc8E y1ebnQvyYW25FfwUI17O4uZoCDE7vls4dhGt96+ueNNXPYmujBBng7gsL0iUV75VIfe8J6vn2aG6a ZPAfuTRRfoC17tS3PZ0HbJv1P5BeTKx+sfpGs0L3+tw7U6PGAgrkBmMo7Y4EQLOk/ZGBMAtr48oz1 ODp7rpGFFHu/QFMmE2Rzpbo44Yj2BbVwHuodmI5KQr7Gywz1TSTAxvyE0uT06c1VVNkVDXeBeHyXX NVVPn66SBi1sP/VgWIzRWLYj9yti124GCrwl0cae7PB2PD5mv3sZQTBrA5TeKG2ipRUAbGSMz64gD Xxu+2rRw==; Received: from 2a02-8389-2341-5b80-d601-7564-c2e0-491c.cable.dynamic.v6.surfer.at ([2a02:8389:2341:5b80:d601:7564:c2e0:491c] helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1wArqO-0000000At2j-3j5h; Thu, 09 Apr 2026 16:03:01 +0000 From: Christoph Hellwig To: Tal Zussman , Jens Axboe , "Matthew Wilcox (Oracle)" , Christian Brauner , "Darrick J. Wong" , Carlos Maiolino , Al Viro , Jan Kara Cc: Dave Chinner , Bart Van Assche , Gao Xiang , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 1/8] block: add BIO_COMPLETE_IN_TASK for task-context completion Date: Thu, 9 Apr 2026 18:02:14 +0200 Message-ID: <20260409160243.1008358-2-hch@lst.de> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260409160243.1008358-1-hch@lst.de> References: <20260409160243.1008358-1-hch@lst.de> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html From: Tal Zussman Some bio completion handlers need to run in task context but bio_endio() can be called from IRQ context (e.g. buffer_head writeback). Add a BIO_COMPLETE_IN_TASK flag that bio submitters can set to request task-context completion of their bi_end_io callback. When bio_endio() sees this flag and is running in non-task context, it queues the bio to a per-cpu lockless list and schedules a delayed work item to call bi_end_io() from task context. The delayed work uses a 1-jiffie delay to allow batches of completions to accumulate before processing. A CPU hotplug dead callback drains any remaining bios from the departing CPU's batch. This will be used to enable RWF_DONTCACHE for block devices, and could be used for other subsystems like fscrypt that need task-context bio completion. Suggested-by: Matthew Wilcox Signed-off-by: Tal Zussman --- block/bio.c | 83 ++++++++++++++++++++++++++++++++++++++- include/linux/blk_types.h | 7 +++- 2 files changed, 88 insertions(+), 2 deletions(-) diff --git a/block/bio.c b/block/bio.c index 641ef0928d73..550eb770bfa6 100644 --- a/block/bio.c +++ b/block/bio.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include "blk.h" @@ -1716,6 +1717,51 @@ void bio_check_pages_dirty(struct bio *bio) } EXPORT_SYMBOL_GPL(bio_check_pages_dirty); +struct bio_complete_batch { + struct llist_head list; + struct delayed_work work; + int cpu; +}; + +static DEFINE_PER_CPU(struct bio_complete_batch, bio_complete_batch); +static struct workqueue_struct *bio_complete_wq; + +static void bio_complete_work_fn(struct work_struct *w) +{ + struct delayed_work *dw = to_delayed_work(w); + struct bio_complete_batch *batch = + container_of(dw, struct bio_complete_batch, work); + struct llist_node *node; + struct bio *bio, *next; + + do { + node = llist_del_all(&batch->list); + if (!node) + break; + + node = llist_reverse_order(node); + llist_for_each_entry_safe(bio, next, node, bi_llist) + bio->bi_end_io(bio); + + if (need_resched()) { + if (!llist_empty(&batch->list)) + mod_delayed_work_on(batch->cpu, + bio_complete_wq, + &batch->work, 0); + break; + } + } while (1); +} + +static void bio_queue_completion(struct bio *bio) +{ + struct bio_complete_batch *batch = this_cpu_ptr(&bio_complete_batch); + + if (llist_add(&bio->bi_llist, &batch->list)) + mod_delayed_work_on(batch->cpu, bio_complete_wq, + &batch->work, 1); +} + static inline bool bio_remaining_done(struct bio *bio) { /* @@ -1790,7 +1836,9 @@ void bio_endio(struct bio *bio) } #endif - if (bio->bi_end_io) + if (!in_task() && bio_flagged(bio, BIO_COMPLETE_IN_TASK)) + bio_queue_completion(bio); + else if (bio->bi_end_io) bio->bi_end_io(bio); } EXPORT_SYMBOL(bio_endio); @@ -1976,6 +2024,24 @@ int bioset_init(struct bio_set *bs, } EXPORT_SYMBOL(bioset_init); +/* + * Drain a dead CPU's deferred bio completions. + */ +static int bio_complete_batch_cpu_dead(unsigned int cpu) +{ + struct bio_complete_batch *batch = + per_cpu_ptr(&bio_complete_batch, cpu); + struct llist_node *node; + struct bio *bio, *next; + + node = llist_del_all(&batch->list); + node = llist_reverse_order(node); + llist_for_each_entry_safe(bio, next, node, bi_llist) + bio->bi_end_io(bio); + + return 0; +} + static int __init init_bio(void) { int i; @@ -1990,6 +2056,21 @@ static int __init init_bio(void) SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); } + for_each_possible_cpu(i) { + struct bio_complete_batch *batch = + per_cpu_ptr(&bio_complete_batch, i); + + init_llist_head(&batch->list); + INIT_DELAYED_WORK(&batch->work, bio_complete_work_fn); + batch->cpu = i; + } + + bio_complete_wq = alloc_workqueue("bio_complete", WQ_MEM_RECLAIM, 0); + if (!bio_complete_wq) + panic("bio: can't allocate bio_complete workqueue\n"); + + cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "block/bio:complete:dead", + NULL, bio_complete_batch_cpu_dead); cpuhp_setup_state_multi(CPUHP_BIO_DEAD, "block/bio:dead", NULL, bio_cpu_dead); diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 8808ee76e73c..0b55159d110d 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -11,6 +11,7 @@ #include #include #include +#include struct bio_set; struct bio; @@ -208,7 +209,10 @@ typedef unsigned int blk_qc_t; * stacking drivers) */ struct bio { - struct bio *bi_next; /* request queue link */ + union { + struct bio *bi_next; /* request queue link */ + struct llist_node bi_llist; /* deferred completion */ + }; struct block_device *bi_bdev; blk_opf_t bi_opf; /* bottom bits REQ_OP, top bits * req_flags. @@ -322,6 +326,7 @@ enum { BIO_REMAPPED, BIO_ZONE_WRITE_PLUGGING, /* bio handled through zone write plugging */ BIO_EMULATES_ZONE_APPEND, /* bio emulates a zone append operation */ + BIO_COMPLETE_IN_TASK, /* complete bi_end_io() in task context */ BIO_FLAG_LAST }; -- 2.47.3