Re: [PATCH v2 04/14] aio: make aio_context_acquire()/aio_context_release() a no-op

[Kevin Wolf <kwolf@xxxxxxxxxx>]

Am 05.12.2023 um 19:20 hat Stefan Hajnoczi geschrieben:
> aio_context_acquire()/aio_context_release() has been replaced by
> fine-grained locking to protect state shared by multiple threads. The
> AioContext lock still plays the role of balancing locking in
> AIO_WAIT_WHILE() and many functions in QEMU either require that the
> AioContext lock is held or not held for this reason. In other words, the
> AioContext lock is purely there for consistency with itself and serves
> no real purpose anymore.
> 
> Stop actually acquiring/releasing the lock in
> aio_context_acquire()/aio_context_release() so that subsequent patches
> can remove callers across the codebase incrementally.
> 
> I have performed "make check" and qemu-iotests stress tests across
> x86-64, ppc64le, and aarch64 to confirm that there are no failures as a
> result of eliminating the lock.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
> Acked-by: Kevin Wolf <kwolf@xxxxxxxxxx>

I knew why I wasn't confident enough to give a R-b... This crashes
qemu-storage-daemon in the qemu-iotests case graph-changes-while-io.

qemu-storage-daemon: ../nbd/server.c:2542: nbd_co_receive_request: Assertion 
`client->recv_coroutine == qemu_coroutine_self()' failed.

(gdb) bt
#0  0x00007fdb00529884 in __pthread_kill_implementation () from /lib64/libc.so.6
#1  0x00007fdb004d8afe in raise () from /lib64/libc.so.6
#2  0x00007fdb004c187f in abort () from /lib64/libc.so.6
#3  0x00007fdb004c179b in __assert_fail_base.cold () from /lib64/libc.so.6
#4  0x00007fdb004d1187 in __assert_fail () from /lib64/libc.so.6
#5  0x0000557f9f9534eb in nbd_co_receive_request (errp=0x7fdafc25eec0, 
request=0x7fdafc25ef10, req=0x7fdaf00159c0) at ../nbd/server.c:2542
#6  nbd_trip (opaque=0x557fa0b33fa0) at ../nbd/server.c:2962
#7  0x0000557f9faa416b in coroutine_trampoline (i0=<optimized out>, 
i1=<optimized out>) at ../util/coroutine-ucontext.c:177
#8  0x00007fdb004efe90 in ?? () from /lib64/libc.so.6
#9  0x00007fdafc35f680 in ?? ()
#10 0x0000000000000000 in ?? ()
(gdb) p *client
$2 = {refcount = 4, close_fn = 0x557f9f95dc40 <nbd_blockdev_client_closed>, exp 
= 0x557fa0b30590, tlscreds = 0x0, tlsauthz = 0x0, sioc = 0x557fa0b33d90, ioc = 
0x557fa0b33d90,
  recv_coroutine = 0x7fdaf0015eb0, send_lock = {locked = 0, ctx = 0x0, 
from_push = {slh_first = 0x0}, to_pop = {slh_first = 0x0}, handoff = 0, 
sequence = 0, holder = 0x0},
  send_coroutine = 0x0, read_yielding = false, quiescing = false, next = 
{tqe_next = 0x0, tqe_circ = {tql_next = 0x0, tql_prev = 0x557fa0b305e8}}, 
nb_requests = 1, closing = false,
  check_align = 1, mode = NBD_MODE_EXTENDED, contexts = {exp = 0x557fa0b30590, 
count = 1, base_allocation = true, allocation_depth = false, bitmaps = 0x0}, 
opt = 7, optlen = 0}
(gdb) p co_tls_current
$3 = (Coroutine *) 0x7fdaf00061d0

Kevin