2ddec1532b
- migration/xbzrle: fix out-of-bounds write with axv512 - migration/xbzrle: use ctz64 to avoid undefined result - Update bench-code for addressing CI problem - AVX512 support for xbzrle_encode_buffer - configure, meson: move AVX tests to meson - target/i386: KVM: allow fast string operations if host supports them - target/i386: add FSRM to TCG - hw/nvme: fix memory leak in nvme_dsm - aio-posix: fix race between epoll upgrade and aio_set_fd_handler() - target/i386: Add SGX aex-notify and EDECCSSA support - hw/usb/imx: Fix out of bounds access in imx_usbphy_read() - target/i386: Set maximum APIC ID to KVM prior to vCPU creation - target/i386: Fix sanity check on max APIC ID / X2APIC enablement Signed-off-by: Fei Xu <xufei30@huawei.com>
83 lines
2.7 KiB
Diff
83 lines
2.7 KiB
Diff
From 4ab8e11adf5878d1f298a682b37d7de4632a3a8b Mon Sep 17 00:00:00 2001
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From: wangmeiyang <wangmeiyang@xfusion.com>
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Date: Fri, 28 Apr 2023 15:22:07 +0800
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Subject: [PATCH] aio-posix: fix race between epoll upgrade and
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aio_set_fd_handler()
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If another thread calls aio_set_fd_handler() while the IOThread event
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loop is upgrading from ppoll(2) to epoll(7) then we might miss new
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AioHandlers. The epollfd will not monitor the new AioHandler's fd,
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resulting in hangs.
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Take the AioHandler list lock while upgrading to epoll. This prevents
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AioHandlers from changing while epoll is being set up. If we cannot lock
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because we're in a nested event loop, then don't upgrade to epoll (it
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will happen next time we're not in a nested call).
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The downside to taking the lock is that the aio_set_fd_handler() thread
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has to wait until the epoll upgrade is finished, which involves many
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epoll_ctl(2) system calls. However, this scenario is rare and I couldn't
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think of another solution that is still simple.
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origin commit: https://gitlab.com/qemu-project/qemu/-/commit/e62da98527fa35fe5f532cded01a33edf9fbe7b2
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Signed-off-by: Meiyang Wang <wangmeiyang@xfusion.com>
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Reported-by: Qing Wang <qinwang@redhat.com>
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Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2090998
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Cc: Paolo Bonzini <pbonzini@redhat.com>
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Cc: Fam Zheng <fam@euphon.net>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-Id: <20230323144859.1338495-1-stefanha@redhat.com>
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Reviewed-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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---
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util/fdmon-epoll.c | 25 ++++++++++++++++++-------
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1 file changed, 18 insertions(+), 7 deletions(-)
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diff --git a/util/fdmon-epoll.c b/util/fdmon-epoll.c
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index e11a8a022e..1683aa1105 100644
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--- a/util/fdmon-epoll.c
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+++ b/util/fdmon-epoll.c
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@@ -127,6 +127,8 @@ static bool fdmon_epoll_try_enable(AioContext *ctx)
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bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
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{
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+ bool ok;
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+
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if (ctx->epollfd < 0) {
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return false;
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}
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@@ -136,14 +138,23 @@ bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
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return false;
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}
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- if (npfd >= EPOLL_ENABLE_THRESHOLD) {
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- if (fdmon_epoll_try_enable(ctx)) {
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- return true;
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- } else {
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- fdmon_epoll_disable(ctx);
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- }
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+ if (npfd < EPOLL_ENABLE_THRESHOLD) {
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+ return false;
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+ }
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+
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+ /* The list must not change while we add fds to epoll */
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+ if (!qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
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+ return false;
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+ }
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+
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+ ok = fdmon_epoll_try_enable(ctx);
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+
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+ qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
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+
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+ if (!ok) {
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+ fdmon_epoll_disable(ctx);
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}
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- return false;
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+ return ok;
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}
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void fdmon_epoll_setup(AioContext *ctx)
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--
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2.27.0
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