Hi Sage,
Sage Weil wrote:
Hi Jim,
Finally had some time to look at this closely. This is great work
nailing down the misbehavior. Here's what confuses me:
- con_work takes con->mutex and does (almost) everything under the
protection of that lock.
- con_close and con_open both take it as well when they twiddle with state
- therefore, after the close/open are called by __reset_osd(), the next
call into con_work should see the OPENING bit is set.
Of course, it doesn't. See below...
[ 2392.366919] libceph: tid 447 timed out on osd20, will reset osd
[ 2392.366922] libceph: osd_client.c:725 : __reset_osd ffff8801955c0000 osd20
[ 2392.366926] libceph: messenger.c:349 : con_close ffff8801955c0030 peer 172.17.40.27:6800
A message times out, __reset_osd signals that connection should be closed; work
queued to connection is discarded.
[ 2392.366934] libceph: messenger.c:369 : con_open ffff8801955c0030 172.17.40.27:6800
__reset_osd signals that connection should be opened.
[ 2392.367237] libceph: messenger.c:2159 : ----- ffff88018f91c600 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367242] libceph: messenger.c:2159 : ----- ffff88018f91d6c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367247] libceph: messenger.c:2159 : ----- ffff88018f920a80 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367251] libceph: messenger.c:2159 : ----- ffff88018f924d80 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367256] libceph: messenger.c:2159 : ----- ffff88018f926480 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367260] libceph: messenger.c:2159 : ----- ffff88018f92f240 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367265] libceph: messenger.c:2159 : ----- ffff88018f930d80 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367269] libceph: messenger.c:2159 : ----- ffff88018be14f00 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367274] libceph: messenger.c:2159 : ----- ffff88018be1b3c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367279] libceph: messenger.c:2159 : ----- ffff88018be210c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367283] libceph: messenger.c:2159 : ----- ffff88018d9c69c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367288] libceph: messenger.c:2159 : ----- ffff88018d85f9c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367293] libceph: messenger.c:2159 : ----- ffff88018daf2300 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367297] libceph: messenger.c:2159 : ----- ffff88018f8b6600 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367302] libceph: messenger.c:2159 : ----- ffff88018be28840 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367307] libceph: messenger.c:2159 : ----- ffff880154105240 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367311] libceph: messenger.c:2159 : ----- ffff88015410a300 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367316] libceph: messenger.c:2159 : ----- ffff88015410f0c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367320] libceph: messenger.c:2159 : ----- ffff880154116d80 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367325] libceph: messenger.c:2159 : ----- ffff8801541176c0 to osd20 42=osd_op len 128+0+524288 -----
[ 2392.367329] libceph: messenger.c:2159 : ----- ffff88015411bb40 to osd20 42=osd_op len 128+0+524288 -----
Outstanding work is requeued to connection.
[ 2397.376206] libceph: messenger.c:2230 : con_keepalive ffff8801955c0030
[ 2402.384140] libceph: messenger.c:2230 : con_keepalive ffff8801955c0030
[ 2407.395283] libceph: messenger.c:2230 : con_keepalive ffff8801955c0030
[ 2411.207412] libceph: messenger.c:2177 : con_revoke ffff8801955c0030 msg ffff88018f91c600 - was on queue
Not sure why the first message was revoked... but that shouldn't matter...
[ 2411.217092] libceph: messenger.c:1708 : try_write start ffff8801955c0030 state 8220 nref 1
[ 2411.225536] libceph: messenger.c:1712 : try_write ffff8801955c0030 out_msg (null) out_kvec_bytes 0
[ 2411.235555] libceph: messenger.c:509 : prepare_write_message ffff8801955c0030 msg ffff88018f91d6c0 seq 1 type 42 len 128+0+524288 128 pgs
[ 2411.256874] libceph: messenger.c:1712 : try_write ffff8801955c0030 out_msg ffff88018f91d6c0 out_kvec_bytes 191
[ 2411.267280] libceph: messenger.c:1790 : try_write done on ffff8801955c0030 ret 0
This picks up the second resent message. But and OPENING is set.. so how
is it that we were in try_write but we didn't pass through the OPENING
test in con_work?
The only way I see this could happen is if this instance
of con_work passed through that test before OPENING was set.
That's what made me think "race".
But, look at the time stamps. 18.85 seconds pass between
con_open and try_write !!
I don't see how that could happen unless the instance of
con_work that called try_write above was stuck in try_read
for most of that 18.85 seconds. I'll check that out.
Also, AFAICS neither ceph_con_open nor ceph_con_close take
con->mutex while they are twiddling bits in con->state. But
here's a fun fact I didn't mention earlier since it didn't
help: putting everything in both ceph_con_open and ceph_con_close
except the call to queue_con(con) under con->mutex didn't help at all.
So it must be something else.
con_work()/try_write() start again on new message.
Note that con_work() did not notice that the connection was marked to
be closed/reopened! This is where things went bad.
Note the connection state: 8220 = 0x201c, and 0x2000 is OPENING.
[ 2412.643178] libceph: messenger.c:1969 : con_work ffff8801955c0030 OPENING
[ 2412.643182] libceph: messenger.c:292 : con_close_socket on ffff8801955c0030 sock ffff8801825a8c00
[ 2412.643197] libceph: messenger.c:162 : ceph_state_change ffff8801955c0030 state = 2076 sk_state = 4
Ok, now we see it, but this should have executed before we ever got to
try_write!
There are a handful of places that drop and re-take con->mutex... I think
it has to be one of those.
OK, I will look at them.
They are:
- prepare_connect_authorizer (before calling ->prepare_authorizer
callback)
- fail_protocol (before calling ->bad_proto callback)
- process_connect RESETSESSION case (before calling ->reset callback)
- process_message (before calling ->dispatch callback)
I think after retaking the lock in each of these cases we need to test for
the CLOSED or OPENING bits and, if set, bail out so that con_work can
restart.
Does that make sense? Can you confirm which case of lock droppage inside
con_work is at fault? (Maybe adding a printk at the top of con_work after
taking the lock too would make it more clear what's going on; currently it
only prints in all the random test_bit cases).
I'm thinking something like the below... does that seem reasonable? I
only did the prepare_authorizer case to start, but the others should be
fixed up too. Compile tested only.
OK, I'll fix them all up and let you know what I learn.
BTW, I looked at the second patch too. Messages should only be requeued
for non-lossy connections, and that's done in ceph_fault by the
list_splice call. The current out_msg is placed on the out_sent list when
we first start, so it is already included in that set. I don't think any
special casing is needed there.
OK, thanks; there's lots of details I haven't fully understood yet.
-- Jim
Thanks for hunting this down!
sage
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