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From: John Snow <jsnow@redhat.com>
To: qemu-block@nongnu.org
Cc: kwolf@redhat.com, qemu-devel@nongnu.org, dgilbert@redhat.com,
	stefanha@redhat.com, pbonzini@redhat.com, pjp@redhat.com,
	John Snow <jsnow@redhat.com>
Subject: [Qemu-devel] [PATCH 0/4] IDE: Do not flush empty drives
Date: Tue,  8 Aug 2017 13:57:07 -0400	[thread overview]
Message-ID: <20170808175711.12203-1-jsnow@redhat.com> (raw)

Patches one and two here are a 2.10 bandaid that avoids a crash.
Patches three and four are a more comprehensive fix as written by
Kevin in another discussion and are being posted here for the sake
of a discussion.

Patch three as written causes hangs in iotests 20, 39, 97, 98, 129,
153, 176, and 185. 124 actually segfaults.

For the purposes of 2.10, we'll likely just want patches 1 and 2
for now.

The problem in a nutshell: incrementing the in-flight counter of the
BDS from the BB layer assumes that every BB always has a BDS. That's
not true; and some devices like IDE have not in the past checked to
see if a given blk_ operation WOULD fail.

This culminates in a new regression where issuing a cache flush to a
CDROM (which is, for some reason, specification valid) will crash QEMU
due to a null dereference when attempting to atomically increment that
backend's in-flight counter.

John Snow (1):
  IDE: Do not flush empty CDROM drives

Kevin Wolf (3):
  IDE: test flush on empty CDROM
  block-backend: shift in-flight counter to BB from BDS
  block-backend: test flush op on empty backend

 block.c                    |  2 +-
 block/block-backend.c      | 40 +++++++++++++++++++++++++-----
 hw/ide/core.c              | 11 +++++---
 tests/Makefile.include     |  2 ++
 tests/ide-test.c           | 19 ++++++++++++++
 tests/test-block-backend.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 125 insertions(+), 11 deletions(-)
 create mode 100644 tests/test-block-backend.c

-- 
2.9.4

             reply	other threads:[~2017-08-08 17:57 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-08 17:57 John Snow [this message]
2017-08-08 17:57 ` [Qemu-devel] [PATCH 1/4] IDE: Do not flush empty CDROM drives John Snow
2017-08-08 19:19   ` Eric Blake
2017-08-09  9:34   ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2017-08-08 17:57 ` [Qemu-devel] [PATCH 2/4] IDE: test flush on empty CDROM John Snow
2017-08-08 19:20   ` Eric Blake
2017-08-08 19:32     ` John Snow
2017-08-09  9:35   ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2017-08-08 17:57 ` [Qemu-devel] [PATCH 3/4] block-backend: shift in-flight counter to BB from BDS John Snow
2017-08-08 18:34   ` Paolo Bonzini
2017-08-08 18:48     ` John Snow
2017-08-09 16:01   ` Kevin Wolf
2017-08-08 17:57 ` [Qemu-devel] [PATCH 4/4] block-backend: test flush op on empty backend John Snow
2017-08-09 16:02   ` Kevin Wolf
2017-08-09 15:53 ` [Qemu-devel] [Qemu-block] [PATCH 0/4] IDE: Do not flush empty drives Stefan Hajnoczi

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