From: "Dr. David Alan Gilbert" <dgilb...@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 <dgilb...@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')
+ sym_fd_coroutine_enter = gdb.parse_and_eval('fd_coroutine_enter')
+
+ while not isnull(cur):
+ entry = cur.dereference()
+ gdb.write('----\n%s\n' % entry)
+
+ # For functions we know, extract the coroutine pointer and
backtrace
+ if cur['fd_read'] == sym_fd_coroutine_enter:
+ # yield_until_fd_readable
+ coptr =
(cur['opaque'].cast(gdb.lookup_type('FDYieldUntilData').pointer()))['co']
+ coptr =
coptr.cast(gdb.lookup_type('CoroutineUContext').pointer())
+ bt_jmpbuf(coptr['env']['__jmpbuf'])
+
+ cur = cur['next']['le_next']
+ gdb.write('----\n')
+
class MtreeCommand(gdb.Command):
'''Display the memory tree hierarchy'''
def __init__(self):
@@ -161,4 +185,5 @@ class MtreeCommand(gdb.Command):
QemuCommand()
CoroutineCommand()
+IOhandlersCommand()
MtreeCommand()
--
2.4.3
