[qemu-xen stable-4.14] aio-posix: disable fdmon-io_uring when GSource is used

[patchbot@xxxxxxx]

commit dcc935873b688a789744ec0a2d0d1b3570d18a6c
Author:     Stefan Hajnoczi <stefanha@xxxxxxxxxx>
AuthorDate: Mon May 11 19:36:30 2020 +0100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue Aug 25 14:30:13 2020 -0500

    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@xxxxxxxxxx>
    Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxx>
    Message-id: 20200511183630.279750-3-stefanha@xxxxxxxxxx
    Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
    (cherry picked from commit ba607ca8bff4d2c2062902f8355657c865ac7c29)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 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;
 }
--
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