Re: [Qemu-devel] [PATCH] gdb command: qemu iohandlers

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Jun 23, 2015 at 03:43:53PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Add a gdb command to print the current set of IOHandlers and
> if one of them is a thread yielding for data print the backtrace.
> 
> Useful for debugging why an incoming migration has stalled, e.g.
> 
>   ----
>   {fd_read = 0x7fd4c8e40d00 <fd_coroutine_enter>, fd_write = 0x0, opaque =
>   0x7fd4b8bfeb00, next = {le_next = 0x7fd4cac81b00, le_prev =
>   0x7fd4c93d2bd0 <io_handlers>}, fd = 22, pollfds_idx = 0, deleted =
>   false}
>   #0  qemu_coroutine_switch (from_=from_@entry=0x7fd4cbb33c00,
>   to_=to_@entry=0x7fd4c8b13a90,
>       action=action@entry=COROUTINE_YIELD) at coroutine-ucontext.c:177
>   #1  0x00007fd4c8e40507 in qemu_coroutine_yield () at
>   qemu-coroutine.c:145
>   #2  0x00007fd4c8e40e75 in yield_until_fd_readable (fd=22) at
>   qemu-coroutine-io.c:90
>   #3  0x00007fd4c8df347f in qemu_rdma_block_for_wrid
>   (rdma=rdma@entry=0x7fd4b8c7e010,
>       wrid_requested=wrid_requested@entry=2000,
>   byte_len=byte_len@entry=0x0) at migration/rdma.c:1510
>   #4  0x00007fd4c8df388f in qemu_rdma_post_send_control
>   (rdma=rdma@entry=0x7fd4b8c7e010, buf=buf@entry=0x0,
>       head=head@entry=0x7fd4b8bfed00) at migration/rdma.c:1608
>   #5  0x00007fd4c8df4b8e in qemu_rdma_exchange_recv (rdma=0x7fd4b8c7e010,
>   head=0x7fd4b8bfed50, expecting=3)
>       at migration/rdma.c:1814
>   #6  0x00007fd4c8df5089 in qemu_rdma_get_buffer (opaque=0x7fd4cba34950,
>   buf=0x7fd4cc24fd20 "TR\022",
>       pos=<optimized out>, size=32768) at migration/rdma.c:2611
>   #7  0x00007fd4c8df000d in qemu_fill_buffer (f=f@entry=0x7fd4cc24fcf0) at
>   migration/qemu-file.c:214
>   #8  0x00007fd4c8df08d4 in qemu_peek_byte (f=f@entry=0x7fd4cc24fcf0,
>   offset=offset@entry=0)
>       at migration/qemu-file.c:447
>   #9  0x00007fd4c8c2cad1 in qemu_loadvm_state (f=f@entry=0x7fd4cc24fcf0)
>   at /root/qemu-world3/migration/savevm.c:1128
>   #10 0x00007fd4c8ded895 in process_incoming_migration_co
>   (opaque=0x7fd4cc24fcf0) at migration/migration.c:145
>   #11 0x00007fd4c8e4112a in coroutine_trampoline (i0=<optimized out>,
>   i1=<optimized out>) at coroutine-ucontext.c:80
>   #12 0x00007fd4c453e0f0 in ?? () from /lib64/libc.so.6
>   #13 0x00007ffee263e870 in ?? ()
>   #14 0x0000000000000000 in ?? ()
>   ----
>   {fd_read = 0x7fd4c8e3ace0 <sigfd_handler>, fd_write = 0x0, opaque = 0x5,
>   next = {le_next = 0x0, le_prev = 0x7fd4cb78a3d8}, fd = 5, pollfds_idx =
>   1, deleted = false}
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  scripts/qemu-gdb.py | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/scripts/qemu-gdb.py b/scripts/qemu-gdb.py
> index 6c7f4fb..2670625 100644
> --- a/scripts/qemu-gdb.py
> +++ b/scripts/qemu-gdb.py
> @@ -102,6 +102,30 @@ class CoroutineCommand(gdb.Command):
>          coroutine_pointer = gdb.parse_and_eval(argv[0]).cast(gdb.lookup_type('CoroutineUContext').pointer())
>          bt_jmpbuf(coroutine_pointer['env']['__jmpbuf'])
>  
> +class IOhandlersCommand(gdb.Command):
> +    '''Display a backtrace for io handlers'''
> +    def __init__(self):
> +        gdb.Command.__init__(self, 'qemu iohandlers', gdb.COMMAND_DATA,
> +                             gdb.COMPLETE_NONE)
> +
> +    def invoke(self, arg, from_tty):
> +        cur = gdb.parse_and_eval('io_handlers.lh_first')

Fam is getting rid of io_handlers and replacing it with an AioContext.

I have CCed him.

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