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From 0bbe9e3a205c48c32f41ddd79292761cc625c747 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Fri, 13 Dec 2013 13:04:35 +0100
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Subject: [PATCH 23/37] block: Allow wait_serialising_requests() at any point
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Message-id: <1392117622-28812-24-git-send-email-kwolf@redhat.com>
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Patchwork-id: 57188
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O-Subject: [RHEL-7.0 qemu-kvm PATCH v2 23/37] block: Allow wait_serialising_requests() at any point
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Bugzilla: 748906
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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We can only have a single wait_serialising_requests() call per request
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because otherwise we can run into deadlocks where requests are waiting
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for each other. The same is true when wait_serialising_requests() is not
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at the very beginning of a request, so that other requests can be issued
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between the start of the tracking and wait_serialising_requests().
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Fix this by changing wait_serialising_requests() to ignore requests that
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are already (directly or indirectly) waiting for the calling request.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Reviewed-by: Benoit Canet <benoit@irqsave.net>
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(cherry picked from commit 6460440f34c709461b84375cfd8a86b27d433225)
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Conflicts:
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include/block/block_int.h
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Conflicts because in RHEL 7 BdrvTrackedRequest is in block.c
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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---
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block.c | 15 ++++++++++++---
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1 file changed, 12 insertions(+), 3 deletions(-)
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---
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block.c | 15 ++++++++++++---
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1 files changed, 12 insertions(+), 3 deletions(-)
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diff --git a/block.c b/block.c
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index 94fd702..fd37037 100644
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--- a/block.c
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+++ b/block.c
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@@ -2047,6 +2047,8 @@ struct BdrvTrackedRequest {
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QLIST_ENTRY(BdrvTrackedRequest) list;
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Coroutine *co; /* owner, used for deadlock detection */
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CoQueue wait_queue; /* coroutines blocked on this request */
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+
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+ struct BdrvTrackedRequest *waiting_for;
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};
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/**
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@@ -2176,9 +2178,16 @@ static void coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
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*/
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assert(qemu_coroutine_self() != req->co);
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- qemu_co_queue_wait(&req->wait_queue);
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- retry = true;
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- break;
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+ /* If the request is already (indirectly) waiting for us, or
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+ * will wait for us as soon as it wakes up, then just go on
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+ * (instead of producing a deadlock in the former case). */
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+ if (!req->waiting_for) {
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+ self->waiting_for = req;
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+ qemu_co_queue_wait(&req->wait_queue);
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+ self->waiting_for = NULL;
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+ retry = true;
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+ break;
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+ }
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}
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}
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} while (retry);
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--
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1.7.1
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