linux-kernel - [PATCH 4/5] blk: use non-rescuing bioset for q->bio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <871su5hhob.fsf@notabene.neil.brown.name>
Date:   Fri, 10 Mar 2017 15:36:20 +1100
From:   NeilBrown <neilb@...e.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Jack Wang <jinpu.wang@...fitbricks.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Pavel Machek <pavel@....cz>, Mike Snitzer <snitzer@...hat.com>,
        Mikulas Patocka <mpatocka@...hat.com>,
        linux-raid@...r.kernel.org,
        device-mapper development <dm-devel@...hat.com>,
        linux-block@...r.kernel.org
Subject: [PATCH 4/5] blk: use non-rescuing bioset for q->bio_split.

A rescuing bioset is only useful if there might be bios from
that same bioset on the bio_list_on_stack queue at a time
when bio_alloc_bioset() is called.  This never applies to
q->bio_split.

Allocations from q->bio_split are only ever made from
blk_queue_split() which is only ever called early in each of
various make_request_fn()s.  The original bio (call this A)
is then passed to generic_make_request() and is placed on
the bio_list_on_stack queue, and the bio that was allocated
from q->bio_split (B) is processed.

The processing of this may cause other bios to be passed to
generic_make_request() or may even cause the bio B itself to
be passed, possible after some prefix has been split off
(using some other bioset).

generic_make_request() now guarantees that all of these bios
(B and dependants) will be fully processed before the tail
of the original bio A gets handled.  None of these early bios
can possible trigger an allocation from the original
q->bio_split as they are either too small to require
splitting or (more likely) are destined for a different queue.

The next time that the original q->bio_split might be used
by this thread is when A is processed again, as it might
still be too big to handle directly.  By this time there
cannot be and other bios allocated fro q->bio_split in the
generic_make_request() queue.  So no rescuing will ever be
needed.

Signed-off-by: NeilBrown <neilb@...e.com>
---
 block/blk-core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index c3992d17dc2c..375006c94c15 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -714,7 +714,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	if (q->id < 0)
 		goto fail_q;

-	q->bio_split = bioset_create_rescued(BIO_POOL_SIZE, 0);
+	q->bio_split = bioset_create(BIO_POOL_SIZE, 0);
 	if (!q->bio_split)
 		goto fail_id;

Download attachment "signature.asc" of type "application/pgp-signature" (833 bytes)