From 3c2d5183f9fa4eac3d17d841e26da65a0181ae7b Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Tue, 29 Aug 2017 13:27:43 +0100 Subject: nbd-client: avoid read_reply_co entry if send failed The following segfault is encountered if the NBD server closes the UNIX domain socket immediately after negotiation: Program terminated with signal SIGSEGV, Segmentation fault. #0 aio_co_schedule (ctx=0x0, co=0xd3c0ff2ef0) at util/async.c:441 441 QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines, (gdb) bt #0 0x000000d3c01a50f8 in aio_co_schedule (ctx=0x0, co=0xd3c0ff2ef0) at util/async.c:441 #1 0x000000d3c012fa90 in nbd_coroutine_end (bs=bs@entry=0xd3c0fec650, request=) at block/nbd-client.c:207 #2 0x000000d3c012fb58 in nbd_client_co_preadv (bs=0xd3c0fec650, offset=0, bytes=, qiov=0x7ffc10a91b20, flags=0) at block/nbd-client.c:237 #3 0x000000d3c0128e63 in bdrv_driver_preadv (bs=bs@entry=0xd3c0fec650, offset=offset@entry=0, bytes=bytes@entry=512, qiov=qiov@entry=0x7ffc10a91b20, flags=0) at block/io.c:836 #4 0x000000d3c012c3e0 in bdrv_aligned_preadv (child=child@entry=0xd3c0ff51d0, req=req@entry=0x7f31885d6e90, offset=offset@entry=0, bytes=bytes@entry=512, align=align@entry=1, qiov=qiov@entry=0x7ffc10a91b20, f +lags=0) at block/io.c:1086 #5 0x000000d3c012c6b8 in bdrv_co_preadv (child=0xd3c0ff51d0, offset=offset@entry=0, bytes=bytes@entry=512, qiov=qiov@entry=0x7ffc10a91b20, flags=flags@entry=0) at block/io.c:1182 #6 0x000000d3c011cc17 in blk_co_preadv (blk=0xd3c0ff4f80, offset=0, bytes=512, qiov=0x7ffc10a91b20, flags=0) at block/block-backend.c:1032 #7 0x000000d3c011ccec in blk_read_entry (opaque=0x7ffc10a91b40) at block/block-backend.c:1079 #8 0x000000d3c01bbb96 in coroutine_trampoline (i0=, i1=) at util/coroutine-ucontext.c:79 #9 0x00007f3196cb8600 in __start_context () at /lib64/libc.so.6 The problem is that nbd_client_init() uses nbd_client_attach_aio_context() -> aio_co_schedule(new_context, client->read_reply_co). Execution of read_reply_co is deferred to a BH which doesn't run until later. In the mean time blk_co_preadv() can be called and nbd_coroutine_end() calls aio_wake() on read_reply_co. At this point in time read_reply_co's ctx isn't set because it has never been entered yet. This patch simplifies the nbd_co_send_request() -> nbd_co_receive_reply() -> nbd_coroutine_end() lifecycle to just nbd_co_send_request() -> nbd_co_receive_reply(). The request is "ended" if an error occurs at any point. Callers no longer have to invoke nbd_coroutine_end(). This cleanup also eliminates the segfault because we don't call aio_co_schedule() to wake up s->read_reply_co if sending the request failed. It is only necessary to wake up s->read_reply_co if a reply was received. Note this only happens with UNIX domain sockets on Linux. It doesn't seem possible to reproduce this with TCP sockets. Suggested-by: Paolo Bonzini Signed-off-by: Stefan Hajnoczi Message-Id: <20170829122745.14309-2-stefanha@redhat.com> Signed-off-by: Eric Blake --- block/nbd-client.c | 25 +++++++++---------------- 1 file changed, 9 insertions(+), 16 deletions(-) (limited to 'block') diff --git a/block/nbd-client.c b/block/nbd-client.c index 25bcaa2..ea728ff 100644 --- a/block/nbd-client.c +++ b/block/nbd-client.c @@ -144,12 +144,12 @@ static int nbd_co_send_request(BlockDriverState *bs, request->handle = INDEX_TO_HANDLE(s, i); if (s->quit) { - qemu_co_mutex_unlock(&s->send_mutex); - return -EIO; + rc = -EIO; + goto err; } if (!s->ioc) { - qemu_co_mutex_unlock(&s->send_mutex); - return -EPIPE; + rc = -EPIPE; + goto err; } if (qiov) { @@ -166,8 +166,13 @@ static int nbd_co_send_request(BlockDriverState *bs, } else { rc = nbd_send_request(s->ioc, request); } + +err: if (rc < 0) { s->quit = true; + s->requests[i].coroutine = NULL; + s->in_flight--; + qemu_co_queue_next(&s->free_sema); } qemu_co_mutex_unlock(&s->send_mutex); return rc; @@ -201,13 +206,6 @@ static void nbd_co_receive_reply(NBDClientSession *s, /* Tell the read handler to read another header. */ s->reply.handle = 0; } -} - -static void nbd_coroutine_end(BlockDriverState *bs, - NBDRequest *request) -{ - NBDClientSession *s = nbd_get_client_session(bs); - int i = HANDLE_TO_INDEX(s, request->handle); s->requests[i].coroutine = NULL; @@ -243,7 +241,6 @@ int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset, } else { nbd_co_receive_reply(client, &request, &reply, qiov); } - nbd_coroutine_end(bs, &request); return -reply.error; } @@ -272,7 +269,6 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset, } else { nbd_co_receive_reply(client, &request, &reply, NULL); } - nbd_coroutine_end(bs, &request); return -reply.error; } @@ -306,7 +302,6 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, } else { nbd_co_receive_reply(client, &request, &reply, NULL); } - nbd_coroutine_end(bs, &request); return -reply.error; } @@ -330,7 +325,6 @@ int nbd_client_co_flush(BlockDriverState *bs) } else { nbd_co_receive_reply(client, &request, &reply, NULL); } - nbd_coroutine_end(bs, &request); return -reply.error; } @@ -355,7 +349,6 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes) } else { nbd_co_receive_reply(client, &request, &reply, NULL); } - nbd_coroutine_end(bs, &request); return -reply.error; } -- cgit v1.1