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From d532d1959bdce14c56e2dd37a5dd013dd7c5ed39 Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Fri, 6 Oct 2017 19:24:06 +0200
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Subject: [PATCH 14/34] nbd-client: avoid read_reply_co entry if send failed
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RH-Author: Eric Blake <eblake@redhat.com>
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Message-id: <20171006192409.29915-2-eblake@redhat.com>
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Patchwork-id: 76913
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O-Subject: [RHEV-7.5 qemu-kvm-rhev PATCH 1/4] nbd-client: avoid read_reply_co entry if send failed
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Bugzilla: 1482478
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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From: Stefan Hajnoczi <stefanha@redhat.com>
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The following segfault is encountered if the NBD server closes the UNIX
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domain socket immediately after negotiation:
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Program terminated with signal SIGSEGV, Segmentation fault.
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#0 aio_co_schedule (ctx=0x0, co=0xd3c0ff2ef0) at util/async.c:441
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441 QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
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(gdb) bt
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#0 0x000000d3c01a50f8 in aio_co_schedule (ctx=0x0, co=0xd3c0ff2ef0) at util/async.c:441
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#1 0x000000d3c012fa90 in nbd_coroutine_end (bs=bs@entry=0xd3c0fec650, request=<optimized out>) at block/nbd-client.c:207
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#2 0x000000d3c012fb58 in nbd_client_co_preadv (bs=0xd3c0fec650, offset=0, bytes=<optimized out>, qiov=0x7ffc10a91b20, flags=0) at block/nbd-client.c:237
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#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
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#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
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+lags=0) at block/io.c:1086
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#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
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#6 0x000000d3c011cc17 in blk_co_preadv (blk=0xd3c0ff4f80, offset=0, bytes=512, qiov=0x7ffc10a91b20, flags=0) at block/block-backend.c:1032
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#7 0x000000d3c011ccec in blk_read_entry (opaque=0x7ffc10a91b40) at block/block-backend.c:1079
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#8 0x000000d3c01bbb96 in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at util/coroutine-ucontext.c:79
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#9 0x00007f3196cb8600 in __start_context () at /lib64/libc.so.6
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The problem is that nbd_client_init() uses
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nbd_client_attach_aio_context() -> aio_co_schedule(new_context,
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client->read_reply_co). Execution of read_reply_co is deferred to a BH
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which doesn't run until later.
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In the mean time blk_co_preadv() can be called and nbd_coroutine_end()
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calls aio_wake() on read_reply_co. At this point in time
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read_reply_co's ctx isn't set because it has never been entered yet.
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This patch simplifies the nbd_co_send_request() ->
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nbd_co_receive_reply() -> nbd_coroutine_end() lifecycle to just
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nbd_co_send_request() -> nbd_co_receive_reply(). The request is "ended"
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if an error occurs at any point. Callers no longer have to invoke
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nbd_coroutine_end().
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This cleanup also eliminates the segfault because we don't call
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aio_co_schedule() to wake up s->read_reply_co if sending the request
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failed. It is only necessary to wake up s->read_reply_co if a reply was
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received.
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Note this only happens with UNIX domain sockets on Linux. It doesn't
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seem possible to reproduce this with TCP sockets.
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Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-Id: <20170829122745.14309-2-stefanha@redhat.com>
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Signed-off-by: Eric Blake <eblake@redhat.com>
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(cherry picked from commit 3c2d5183f9fa4eac3d17d841e26da65a0181ae7b)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block/nbd-client.c | 25 +++++++++----------------
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1 file changed, 9 insertions(+), 16 deletions(-)
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diff --git a/block/nbd-client.c b/block/nbd-client.c
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index 25bcaa2..ea728ff 100644
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--- a/block/nbd-client.c
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+++ b/block/nbd-client.c
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@@ -144,12 +144,12 @@ static int nbd_co_send_request(BlockDriverState *bs,
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request->handle = INDEX_TO_HANDLE(s, i);
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if (s->quit) {
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- qemu_co_mutex_unlock(&s->send_mutex);
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- return -EIO;
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+ rc = -EIO;
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+ goto err;
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}
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if (!s->ioc) {
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- qemu_co_mutex_unlock(&s->send_mutex);
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- return -EPIPE;
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+ rc = -EPIPE;
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+ goto err;
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}
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if (qiov) {
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@@ -166,8 +166,13 @@ static int nbd_co_send_request(BlockDriverState *bs,
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} else {
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rc = nbd_send_request(s->ioc, request);
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}
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+
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+err:
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if (rc < 0) {
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s->quit = true;
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+ s->requests[i].coroutine = NULL;
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+ s->in_flight--;
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+ qemu_co_queue_next(&s->free_sema);
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}
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qemu_co_mutex_unlock(&s->send_mutex);
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return rc;
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@@ -201,13 +206,6 @@ static void nbd_co_receive_reply(NBDClientSession *s,
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/* Tell the read handler to read another header. */
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s->reply.handle = 0;
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}
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-}
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-
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-static void nbd_coroutine_end(BlockDriverState *bs,
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- NBDRequest *request)
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-{
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- NBDClientSession *s = nbd_get_client_session(bs);
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- int i = HANDLE_TO_INDEX(s, request->handle);
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s->requests[i].coroutine = NULL;
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@@ -243,7 +241,6 @@ int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset,
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} else {
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nbd_co_receive_reply(client, &request, &reply, qiov);
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}
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- nbd_coroutine_end(bs, &request);
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return -reply.error;
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}
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@@ -272,7 +269,6 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
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} else {
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nbd_co_receive_reply(client, &request, &reply, NULL);
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}
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- nbd_coroutine_end(bs, &request);
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return -reply.error;
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}
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@@ -306,7 +302,6 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
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} else {
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nbd_co_receive_reply(client, &request, &reply, NULL);
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}
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- nbd_coroutine_end(bs, &request);
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return -reply.error;
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}
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@@ -330,7 +325,6 @@ int nbd_client_co_flush(BlockDriverState *bs)
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} else {
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nbd_co_receive_reply(client, &request, &reply, NULL);
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}
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- nbd_coroutine_end(bs, &request);
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return -reply.error;
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}
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@@ -355,7 +349,6 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes)
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} else {
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nbd_co_receive_reply(client, &request, &reply, NULL);
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}
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- nbd_coroutine_end(bs, &request);
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return -reply.error;
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}
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--
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1.8.3.1
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