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[Qemu-discuss] Why Qemu get the io event , while Qemu system reset? Is i

From: EricSong
Subject: [Qemu-discuss] Why Qemu get the io event , while Qemu system reset? Is it unreasonable?
Date: Fri, 9 Jan 2015 10:42:23 +0800

Hi, All

   I traced the Qemu code, and I found a debug information but not unreasonable in my opinion.

   Qemu main process always get the command --- RESET,  by qemu_reset_requested() in main_loop_should_exit(), and the thread qemu_tcg_cpu_thread_fn() always running.

   While RESET is got , main process will execute followings:

    if (qemu_reset_requested()) {





        if (runstate_needs_reset()) {





After pause_all_vcpus(), the qemu_tcg_cpu_thread_fn() will is under qemu_tcg_wait_io_event(). But never execute tcg_exec_all().

After qemu_system_reset(VMRESET_REPORT), the system is under reset state, then the qemu_tcg_cpu_thread_fn() will is still under qemu_tcg_wait_io_event().

After resume_all_vcpus(),the qemu_tcg_cpu_thread_fn() can receive the event and exit qemu_tcg_wait_io_event(), then start to execute tcg_exec_all().


I think it is reasonable sequence about system reset phase.

But from my testing, I found qemu_tcg_cpu_thread_fn() exit qemu_tcg_wait_io_event(), while system resetting. How to explain? The debug information is followings:


add system 1 reset starting!!!                               -----   before qemu_system_reset

Eric add devices reset!!!                                 -----   enter qemu_system_reset and before devices reset

Eric add x86 cpu reset handler real execution       -----   some reset handler (x86 cpu reset handler)

Eric add (new start)cs = ffff0000; eip=fff0!!!    --------\

(bf wait tcg_exec)cs = ffff0000; eip=fff0!!!      ---------- Why appear here?

Eric add cs = ffff0000; eip=fff0!!!             ---------/

Eric add devices reset end!!!                             -----   after devices reset

Eric add system 1 reset ended!!!                            -----   after qemu_system_reset

Eric add (bf cpu_resume)cs = ffff0000; eip=fff0!!!               -----  resume_all_vcpus();

Eric add (new start)cs = ffff0000; eip=fff0!!!                   -----  after qemu_tcg_wait_io_event()

(bf tcg_exec_all)cs = ffff0000; eip=fff0!!!                      -----  before tcg_exec_all()

Eric add cs = ffff0000; eip=fff0!!!                            -----  start to execute tcg_exec_all()


Thank you very much!




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