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[Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining
From: |
Max Reitz |
Subject: |
[Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS |
Date: |
Thu, 9 Nov 2017 21:43:15 +0100 |
Draining a BDS may lead to graph modifications, which in turn may result
in it and other BDS being stripped of their current references. If
bdrv_drain_all_begin() and bdrv_drain_all_end() do not keep strong
references themselves, the BDS they are trying to drain (or undrain) may
disappear right under their feet -- or, more specifically, under the
feet of BDRV_POLL_WHILE() in bdrv_drain_recurse().
This fixes an occasional hang of iotest 194.
Signed-off-by: Max Reitz <address@hidden>
---
block/io.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 44 insertions(+), 3 deletions(-)
diff --git a/block/io.c b/block/io.c
index 3d5ef2cabe..a0a2833e8e 100644
--- a/block/io.c
+++ b/block/io.c
@@ -340,7 +340,10 @@ void bdrv_drain_all_begin(void)
bool waited = true;
BlockDriverState *bs;
BdrvNextIterator it;
- GSList *aio_ctxs = NULL, *ctx;
+ GSList *aio_ctxs = NULL, *ctx, *bs_list = NULL, *bs_list_entry;
+
+ /* Must be called from the main loop */
+ assert(qemu_get_current_aio_context() == qemu_get_aio_context());
block_job_pause_all();
@@ -355,6 +358,12 @@ void bdrv_drain_all_begin(void)
if (!g_slist_find(aio_ctxs, aio_context)) {
aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
}
+
+ /* Keep a strong reference to all root BDS and copy them into
+ * an own list because draining them may lead to graph
+ * modifications. */
+ bdrv_ref(bs);
+ bs_list = g_slist_prepend(bs_list, bs);
}
/* Note that completion of an asynchronous I/O operation can trigger any
@@ -370,7 +379,11 @@ void bdrv_drain_all_begin(void)
AioContext *aio_context = ctx->data;
aio_context_acquire(aio_context);
- for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+ for (bs_list_entry = bs_list; bs_list_entry;
+ bs_list_entry = bs_list_entry->next)
+ {
+ bs = bs_list_entry->data;
+
if (aio_context == bdrv_get_aio_context(bs)) {
waited |= bdrv_drain_recurse(bs, true);
}
@@ -379,24 +392,52 @@ void bdrv_drain_all_begin(void)
}
}
+ for (bs_list_entry = bs_list; bs_list_entry;
+ bs_list_entry = bs_list_entry->next)
+ {
+ bdrv_unref(bs_list_entry->data);
+ }
+
g_slist_free(aio_ctxs);
+ g_slist_free(bs_list);
}
void bdrv_drain_all_end(void)
{
BlockDriverState *bs;
BdrvNextIterator it;
+ GSList *bs_list = NULL, *bs_list_entry;
+
+ /* Must be called from the main loop */
+ assert(qemu_get_current_aio_context() == qemu_get_aio_context());
+ /* Keep a strong reference to all root BDS and copy them into an
+ * own list because draining them may lead to graph modifications.
+ */
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
- AioContext *aio_context = bdrv_get_aio_context(bs);
+ bdrv_ref(bs);
+ bs_list = g_slist_prepend(bs_list, bs);
+ }
+
+ for (bs_list_entry = bs_list; bs_list_entry;
+ bs_list_entry = bs_list_entry->next)
+ {
+ AioContext *aio_context;
+
+ bs = bs_list_entry->data;
+ aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
aio_enable_external(aio_context);
bdrv_parent_drained_end(bs);
bdrv_drain_recurse(bs, false);
aio_context_release(aio_context);
+
+ bdrv_unref(bs);
}
+ g_slist_free(bs_list);
+
block_job_resume_all();
}
--
2.13.6
- [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS,
Max Reitz <=
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Eric Blake, 2017/11/09
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Fam Zheng, 2017/11/09
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Kevin Wolf, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Fam Zheng, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Max Reitz, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Fam Zheng, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Kevin Wolf, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Max Reitz, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Kevin Wolf, 2017/11/10
- Re: [Qemu-devel] [PATCH for-2.11] block: Keep strong reference when draining all BDS, Max Reitz, 2017/11/10