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authorFam Zheng <famz@redhat.com>2017-04-18 22:30:44 +0800
committerFam Zheng <famz@redhat.com>2017-04-18 22:56:28 +0800
commit91af091f92358c2ff828fa1def1a7bea9b701cdf (patch)
treec5fa1810e634b8bd725bd2eaafccffb4362c1552
parent178bd438af5c95deef5073416c60396f88e97ec9 (diff)
downloadqemu-arm-91af091f92358c2ff828fa1def1a7bea9b701cdf.tar.gz
block: Drain BH in bdrv_drained_begin
During block job completion, nothing is preventing block_job_defer_to_main_loop_bh from being called in a nested aio_poll(), which is a trouble, such as in this code path: qmp_block_commit commit_active_start bdrv_reopen bdrv_reopen_multiple bdrv_reopen_prepare bdrv_flush aio_poll aio_bh_poll aio_bh_call block_job_defer_to_main_loop_bh stream_complete bdrv_reopen block_job_defer_to_main_loop_bh is the last step of the stream job, which should have been "paused" by the bdrv_drained_begin/end in bdrv_reopen_multiple, but it is not done because it's in the form of a main loop BH. Similar to why block jobs should be paused between drained_begin and drained_end, BHs they schedule must be excluded as well. To achieve this, this patch forces draining the BH in BDRV_POLL_WHILE. As a side effect this fixes a hang in block_job_detach_aio_context during system_reset when a block job is ready: #0 0x0000555555aa79f3 in bdrv_drain_recurse #1 0x0000555555aa825d in bdrv_drained_begin #2 0x0000555555aa8449 in bdrv_drain #3 0x0000555555a9c356 in blk_drain #4 0x0000555555aa3cfd in mirror_drain #5 0x0000555555a66e11 in block_job_detach_aio_context #6 0x0000555555a62f4d in bdrv_detach_aio_context #7 0x0000555555a63116 in bdrv_set_aio_context #8 0x0000555555a9d326 in blk_set_aio_context #9 0x00005555557e38da in virtio_blk_data_plane_stop #10 0x00005555559f9d5f in virtio_bus_stop_ioeventfd #11 0x00005555559fa49b in virtio_bus_stop_ioeventfd #12 0x00005555559f6a18 in virtio_pci_stop_ioeventfd #13 0x00005555559f6a18 in virtio_pci_reset #14 0x00005555559139a9 in qdev_reset_one #15 0x0000555555916738 in qbus_walk_children #16 0x0000555555913318 in qdev_walk_children #17 0x0000555555916738 in qbus_walk_children #18 0x00005555559168ca in qemu_devices_reset #19 0x000055555581fcbb in pc_machine_reset #20 0x00005555558a4d96 in qemu_system_reset #21 0x000055555577157a in main_loop_should_exit #22 0x000055555577157a in main_loop #23 0x000055555577157a in main The rationale is that the loop in block_job_detach_aio_context cannot make any progress in pausing/completing the job, because bs->in_flight is 0, so bdrv_drain doesn't process the block_job_defer_to_main_loop BH. With this patch, it does. Reported-by: Jeff Cody <jcody@redhat.com> Signed-off-by: Fam Zheng <famz@redhat.com> Message-Id: <20170418143044.12187-3-famz@redhat.com> Reviewed-by: Jeff Cody <jcody@redhat.com> Tested-by: Jeff Cody <jcody@redhat.com> Signed-off-by: Fam Zheng <famz@redhat.com>
-rw-r--r--include/block/block.h22
1 files changed, 14 insertions, 8 deletions
diff --git a/include/block/block.h b/include/block/block.h
index 97d4330292..5ddc0cf21b 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -381,12 +381,13 @@ void bdrv_drain_all(void);
#define BDRV_POLL_WHILE(bs, cond) ({ \
bool waited_ = false; \
+ bool busy_ = true; \
BlockDriverState *bs_ = (bs); \
AioContext *ctx_ = bdrv_get_aio_context(bs_); \
if (aio_context_in_iothread(ctx_)) { \
- while ((cond)) { \
- aio_poll(ctx_, true); \
- waited_ = true; \
+ while ((cond) || busy_) { \
+ busy_ = aio_poll(ctx_, (cond)); \
+ waited_ |= !!(cond) | busy_; \
} \
} else { \
assert(qemu_get_current_aio_context() == \
@@ -398,11 +399,16 @@ void bdrv_drain_all(void);
*/ \
assert(!bs_->wakeup); \
bs_->wakeup = true; \
- while ((cond)) { \
- aio_context_release(ctx_); \
- aio_poll(qemu_get_aio_context(), true); \
- aio_context_acquire(ctx_); \
- waited_ = true; \
+ while (busy_) { \
+ if ((cond)) { \
+ waited_ = busy_ = true; \
+ aio_context_release(ctx_); \
+ aio_poll(qemu_get_aio_context(), true); \
+ aio_context_acquire(ctx_); \
+ } else { \
+ busy_ = aio_poll(ctx_, false); \
+ waited_ |= busy_; \
+ } \
} \
bs_->wakeup = false; \
} \