[PATCH for-10.2] Revert "nvme: Fix coroutine waking"

[Hanna Czenczek <hreitz@redhat.com>]

This reverts commit 0f142cbd919fcb6cea7aa176f7e4939925806dd9.

Lukáš Doktor reported a simple single-threaded nvme test case hanging
and bisected it to this commit.  While we are still investigating, it is
best to revert the commit for now.

(This breaks multiqueue for nvme, but better to have single-queue
working than neither.)

Cc: qemu-stable@nongnu.org
Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
---
 block/nvme.c | 56 +++++++++++++++++++++++++---------------------------
 1 file changed, 27 insertions(+), 29 deletions(-)

diff --git a/block/nvme.c b/block/nvme.c
index 919e14cef9..c3d3b99d1f 100644
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -1200,36 +1200,26 @@ fail:
 
 typedef struct {
     Coroutine *co;
-    bool skip_yield;
     int ret;
+    AioContext *ctx;
 } NVMeCoData;
 
+static void nvme_rw_cb_bh(void *opaque)
+{
+    NVMeCoData *data = opaque;
+    qemu_coroutine_enter(data->co);
+}
+
 /* Put into NVMeRequest.cb, so runs in the BDS's main AioContext */
 static void nvme_rw_cb(void *opaque, int ret)
 {
     NVMeCoData *data = opaque;
-
     data->ret = ret;
-
-    if (data->co == qemu_coroutine_self()) {
-        /*
-         * Fast path: We are inside of the request coroutine (through
-         * nvme_submit_command, nvme_deferred_fn, nvme_process_completion).
-         * We can set data->skip_yield here to keep the coroutine from
-         * yielding, and then we don't need to schedule a BH to wake it.
-         */
-        data->skip_yield = true;
-    } else {
-        /*
-         * Safe to call: The case where we run in the request coroutine is
-         * handled above, so we must be independent of it; and without
-         * skip_yield set, the coroutine will yield.
-         * No need to release NVMeQueuePair.lock (we are called without it
-         * held).  (Note: If we enter the coroutine here, @data will
-         * probably be dangling once aio_co_wake() returns.)
-         */
-        aio_co_wake(data->co);
+    if (!data->co) {
+        /* The rw coroutine hasn't yielded, don't try to enter. */
+        return;
     }
+    replay_bh_schedule_oneshot_event(data->ctx, nvme_rw_cb_bh, data);
 }
 
 static coroutine_fn int nvme_co_prw_aligned(BlockDriverState *bs,
@@ -1253,7 +1243,7 @@ static coroutine_fn int nvme_co_prw_aligned(BlockDriverState *bs,
         .cdw12 = cpu_to_le32(cdw12),
     };
     NVMeCoData data = {
-        .co = qemu_coroutine_self(),
+        .ctx = bdrv_get_aio_context(bs),
         .ret = -EINPROGRESS,
     };
 
@@ -1270,7 +1260,9 @@ static coroutine_fn int nvme_co_prw_aligned(BlockDriverState *bs,
         return r;
     }
     nvme_submit_command(ioq, req, &cmd, nvme_rw_cb, &data);
-    if (!data.skip_yield) {
+
+    data.co = qemu_coroutine_self();
+    while (data.ret == -EINPROGRESS) {
         qemu_coroutine_yield();
     }
 
@@ -1366,7 +1358,7 @@ static coroutine_fn int nvme_co_flush(BlockDriverState *bs)
         .nsid = cpu_to_le32(s->nsid),
     };
     NVMeCoData data = {
-        .co = qemu_coroutine_self(),
+        .ctx = bdrv_get_aio_context(bs),
         .ret = -EINPROGRESS,
     };
 
@@ -1374,7 +1366,9 @@ static coroutine_fn int nvme_co_flush(BlockDriverState *bs)
     req = nvme_get_free_req(ioq);
     assert(req);
     nvme_submit_command(ioq, req, &cmd, nvme_rw_cb, &data);
-    if (!data.skip_yield) {
+
+    data.co = qemu_coroutine_self();
+    if (data.ret == -EINPROGRESS) {
         qemu_coroutine_yield();
     }
 
@@ -1415,7 +1409,7 @@ static coroutine_fn int nvme_co_pwrite_zeroes(BlockDriverState *bs,
     };
 
     NVMeCoData data = {
-        .co = qemu_coroutine_self(),
+        .ctx = bdrv_get_aio_context(bs),
         .ret = -EINPROGRESS,
     };
 
@@ -1435,7 +1429,9 @@ static coroutine_fn int nvme_co_pwrite_zeroes(BlockDriverState *bs,
     assert(req);
 
     nvme_submit_command(ioq, req, &cmd, nvme_rw_cb, &data);
-    if (!data.skip_yield) {
+
+    data.co = qemu_coroutine_self();
+    while (data.ret == -EINPROGRESS) {
         qemu_coroutine_yield();
     }
 
@@ -1463,7 +1459,7 @@ static int coroutine_fn nvme_co_pdiscard(BlockDriverState *bs,
     };
 
     NVMeCoData data = {
-        .co = qemu_coroutine_self(),
+        .ctx = bdrv_get_aio_context(bs),
         .ret = -EINPROGRESS,
     };
 
@@ -1508,7 +1504,9 @@ static int coroutine_fn nvme_co_pdiscard(BlockDriverState *bs,
     trace_nvme_dsm(s, offset, bytes);
 
     nvme_submit_command(ioq, req, &cmd, nvme_rw_cb, &data);
-    if (!data.skip_yield) {
+
+    data.co = qemu_coroutine_self();
+    while (data.ret == -EINPROGRESS) {
         qemu_coroutine_yield();
     }
 
-- 
2.52.0