From b474155fdc38f86f516c14ba9a6f934616d589ef Mon Sep 17 00:00:00 2001 From: Andrew Jones Date: Wed, 4 Aug 2021 03:27:22 -0400 Subject: [PATCH 1/2] aio-wait: delegate polling of main AioContext if BQL not held RH-Author: Andrew Jones Message-id: <20210729134448.4995-2-drjones@redhat.com> Patchwork-id: 101935 O-Subject: [RHEL-8.5.0 qemu-kvm PATCH v2 1/2] aio-wait: delegate polling of main AioContext if BQL not held Bugzilla: 1969848 RH-Acked-by: Gavin Shan RH-Acked-by: Auger Eric RH-Acked-by: Stefan Hajnoczi From: Paolo Bonzini Any thread that is not a iothread returns NULL for qemu_get_current_aio_context(). As a result, it would also return true for in_aio_context_home_thread(qemu_get_aio_context()), causing AIO_WAIT_WHILE to invoke aio_poll() directly. This is incorrect if the BQL is not held, because aio_poll() does not expect to run concurrently from multiple threads, and it can actually happen when savevm writes to the vmstate file from the migration thread. Therefore, restrict in_aio_context_home_thread to return true for the main AioContext only if the BQL is held. The function is moved to aio-wait.h because it is mostly used there and to avoid a circular reference between main-loop.h and block/aio.h. Signed-off-by: Paolo Bonzini Message-Id: <20200407140746.8041-5-pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi (cherry picked from commit 3c18a92dc4b55ca8cc37a755ed119f11c0f34099) Signed-off-by: Andrew Jones Signed-off-by: Miroslav Rezanina --- include/block/aio-wait.h | 22 ++++++++++++++++++++++ include/block/aio.h | 29 ++++++++++------------------- 2 files changed, 32 insertions(+), 19 deletions(-) diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h index afeeb18f95..716d2639df 100644 --- a/include/block/aio-wait.h +++ b/include/block/aio-wait.h @@ -26,6 +26,7 @@ #define QEMU_AIO_WAIT_H #include "block/aio.h" +#include "qemu/main-loop.h" /** * AioWait: @@ -124,4 +125,25 @@ void aio_wait_kick(void); */ void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); +/** + * in_aio_context_home_thread: + * @ctx: the aio context + * + * Return whether we are running in the thread that normally runs @ctx. Note + * that acquiring/releasing ctx does not affect the outcome, each AioContext + * still only has one home thread that is responsible for running it. + */ +static inline bool in_aio_context_home_thread(AioContext *ctx) +{ + if (ctx == qemu_get_current_aio_context()) { + return true; + } + + if (ctx == qemu_get_aio_context()) { + return qemu_mutex_iothread_locked(); + } else { + return false; + } +} + #endif /* QEMU_AIO_WAIT_H */ diff --git a/include/block/aio.h b/include/block/aio.h index 6b0d52f732..9d28e247df 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -60,12 +60,16 @@ struct AioContext { QLIST_HEAD(, AioHandler) aio_handlers; /* Used to avoid unnecessary event_notifier_set calls in aio_notify; - * accessed with atomic primitives. If this field is 0, everything - * (file descriptors, bottom halves, timers) will be re-evaluated - * before the next blocking poll(), thus the event_notifier_set call - * can be skipped. If it is non-zero, you may need to wake up a - * concurrent aio_poll or the glib main event loop, making - * event_notifier_set necessary. + * only written from the AioContext home thread, or under the BQL in + * the case of the main AioContext. However, it is read from any + * thread so it is still accessed with atomic primitives. + * + * If this field is 0, everything (file descriptors, bottom halves, + * timers) will be re-evaluated before the next blocking poll() or + * io_uring wait; therefore, the event_notifier_set call can be + * skipped. If it is non-zero, you may need to wake up a concurrent + * aio_poll or the glib main event loop, making event_notifier_set + * necessary. * * Bit 0 is reserved for GSource usage of the AioContext, and is 1 * between a call to aio_ctx_prepare and the next call to aio_ctx_check. @@ -580,19 +584,6 @@ void aio_co_enter(AioContext *ctx, struct Coroutine *co); */ AioContext *qemu_get_current_aio_context(void); -/** - * in_aio_context_home_thread: - * @ctx: the aio context - * - * Return whether we are running in the thread that normally runs @ctx. Note - * that acquiring/releasing ctx does not affect the outcome, each AioContext - * still only has one home thread that is responsible for running it. - */ -static inline bool in_aio_context_home_thread(AioContext *ctx) -{ - return ctx == qemu_get_current_aio_context(); -} - /** * aio_context_setup: * @ctx: the aio context -- 2.27.0