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qemu-5.0.0-2 

Fix iouring hang (bz #1823751)
This commit is contained in:
Cole Robinson 2020-05-13 13:34:26 -04:00
parent 8c45437b3a
commit 3da886a924
3 changed files with 161 additions and 1 deletions
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64
0001-aio-posix-don-t-duplicate-fd-handler-deletion-in-fdm.patch Normal file
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@ -0,0 +1,64 @@
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 11 May 2020 19:36:29 +0100
Subject: [PATCH] aio-posix: don't duplicate fd handler deletion in
fdmon_io_uring_destroy()
The io_uring file descriptor monitoring implementation has an internal
list of fd handlers that are pending submission to io_uring.
fdmon_io_uring_destroy() deletes all fd handlers on the list.
Don't delete fd handlers directly in fdmon_io_uring_destroy() for two
reasons:
1. This duplicates the aio-posix.c AioHandler deletion code and could
become outdated if the struct changes.
2. Only handlers with the FDMON_IO_URING_REMOVE flag set are safe to
remove. If the flag is not set then something still has a pointer to
the fd handler. Let aio-posix.c and its user worry about that. In
practice this isn't an issue because fdmon_io_uring_destroy() is only
called when shutting down so all users have removed their fd
handlers, but the next patch will need this!
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
util/aio-posix.c | 1 +
util/fdmon-io_uring.c | 13 ++++++++++---
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/util/aio-posix.c b/util/aio-posix.c
index c3613d299e..8af334ab19 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -679,6 +679,7 @@ void aio_context_destroy(AioContext *ctx)
{
fdmon_io_uring_destroy(ctx);
fdmon_epoll_disable(ctx);
+ aio_free_deleted_handlers(ctx);
}
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index d5a80ed6fb..1d14177df0 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -342,11 +342,18 @@ void fdmon_io_uring_destroy(AioContext *ctx)
io_uring_queue_exit(&ctx->fdmon_io_uring);
- /* No need to submit these anymore, just free them. */
+ /* Move handlers due to be removed onto the deleted list */
while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {
+ unsigned flags = atomic_fetch_and(&node->flags,
+ ~(FDMON_IO_URING_PENDING |
+ FDMON_IO_URING_ADD |
+ FDMON_IO_URING_REMOVE));
+
+ if (flags & FDMON_IO_URING_REMOVE) {
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
+ }
+
QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
- QLIST_REMOVE(node, node);
- g_free(node);
}
ctx->fdmon_ops = &fdmon_poll_ops;

88
0002-aio-posix-disable-fdmon-io_uring-when-GSource-is-use.patch Normal file
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@ -0,0 +1,88 @@
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 11 May 2020 19:36:30 +0100
Subject: [PATCH] aio-posix: disable fdmon-io_uring when GSource is used
The glib event loop does not call fdmon_io_uring_wait() so fd handlers
waiting to be submitted build up in the list. There is no benefit is
using io_uring when the glib GSource is being used, so disable it
instead of implementing a more complex fix.
This fixes a memory leak where AioHandlers would build up and increasing
amounts of CPU time were spent iterating them in aio_pending(). The
symptom is that guests become slow when QEMU is built with io_uring
support.
Buglink: https://bugs.launchpad.net/qemu/+bug/1877716
Fixes: 73fd282e7b6dd4e4ea1c3bbb3d302c8db51e4ccf ("aio-posix: add io_uring fd monitoring implementation")
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
include/block/aio.h | 3 +++
util/aio-posix.c | 12 ++++++++++++
util/aio-win32.c | 4 ++++
util/async.c | 1 +
4 files changed, 20 insertions(+)
diff --git a/include/block/aio.h b/include/block/aio.h
index 62ed954344..b2f703fa3f 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -701,6 +701,9 @@ void aio_context_setup(AioContext *ctx);
*/
void aio_context_destroy(AioContext *ctx);
+/* Used internally, do not call outside AioContext code */
+void aio_context_use_g_source(AioContext *ctx);
+
/**
* aio_context_set_poll_params:
* @ctx: the aio context
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 8af334ab19..1b2a3af65b 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -682,6 +682,18 @@ void aio_context_destroy(AioContext *ctx)
aio_free_deleted_handlers(ctx);
}
+void aio_context_use_g_source(AioContext *ctx)
+{
+ /*
+ * Disable io_uring when the glib main loop is used because it doesn't
+ * support mixed glib/aio_poll() usage. It relies on aio_poll() being
+ * called regularly so that changes to the monitored file descriptors are
+ * submitted, otherwise a list of pending fd handlers builds up.
+ */
+ fdmon_io_uring_destroy(ctx);
+ aio_free_deleted_handlers(ctx);
+}
+
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
int64_t grow, int64_t shrink, Error **errp)
{
diff --git a/util/aio-win32.c b/util/aio-win32.c
index 729d533faf..953c56ab48 100644
--- a/util/aio-win32.c
+++ b/util/aio-win32.c
@@ -414,6 +414,10 @@ void aio_context_destroy(AioContext *ctx)
{
}
+void aio_context_use_g_source(AioContext *ctx)
+{
+}
+
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
int64_t grow, int64_t shrink, Error **errp)
{
diff --git a/util/async.c b/util/async.c
index 3165a28f2f..1319eee3bc 100644
--- a/util/async.c
+++ b/util/async.c
@@ -362,6 +362,7 @@ static GSourceFuncs aio_source_funcs = {
GSource *aio_get_g_source(AioContext *ctx)
{
+ aio_context_use_g_source(ctx);
g_source_ref(&ctx->source);
return &ctx->source;
}

10
qemu.spec
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@ -161,7 +161,7 @@
Summary: QEMU is a FAST! processor emulator
Name: qemu
Version: 5.0.0
Release: 1%{?rcrel}%{?dist}
Release: 2%{?rcrel}%{?dist}
Epoch: 2
License: GPLv2 and BSD and MIT and CC-BY
URL: http://www.qemu.org/
@ -185,6 +185,11 @@ Source20: kvm-x86.modprobe.conf
# /etc/security/limits.d/95-kvm-ppc64-memlock.conf
Source21: 95-kvm-ppc64-memlock.conf
# Fix iouring hang (bz #1823751)
# https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg02728.html
Patch0001: 0001-aio-posix-don-t-duplicate-fd-handler-deletion-in-fdm.patch
Patch0002: 0002-aio-posix-disable-fdmon-io_uring-when-GSource-is-use.patch
# documentation deps
BuildRequires: texinfo
@ -1834,6 +1839,9 @@ getent passwd qemu >/dev/null || \
%changelog
* Wed May 13 2020 Cole Robinson <crobinso@redhat.com> - 5.0.0-2
- Fix iouring hang (bz #1823751)
* Wed May 06 2020 Cole Robinson <crobinso@redhat.com> - 5.0.0-1
- Update to version 5.0.0