From 31ae365f6c13d1bdad9d4eefe6e9f00928e5dd64 Mon Sep 17 00:00:00 2001
From: tangbinzy <tangbin_yewu@cmss.chinamobile.com>
Date: Wed, 26 Jul 2023 02:50:59 +0000
Subject: [PATCH] ide: Increment BB in-flight counter for TRIM BH mainline
 inclusion commit 7e5cdb345f77d76cb4877fe6230c4e17a7d0d0ca category: bugfix
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When we still have an AIOCB registered for DMA operations, we try to
settle the respective operation by draining the BlockBackend associated
with the IDE device.

However, this assumes that every DMA operation is associated with an
increment of the BlockBackend’s in-flight counter (e.g. through some
ongoing I/O operation), so that draining the BB until its in-flight
counter reaches 0 will settle all DMA operations.  That is not the case:
For TRIM, the guest can issue a zero-length operation that will not
result in any I/O operation forwarded to the BlockBackend, and also not
increment the in-flight counter in any other way.  In such a case,
blk_drain() will be a no-op if no other operations are in flight.

It is clear that if blk_drain() is a no-op, the value of
s->bus->dma->aiocb will not change between checking it in the `if`
condition and asserting that it is NULL after blk_drain().

The particular problem is that ide_issue_trim() creates a BH
(ide_trim_bh_cb()) to settle the TRIM request: iocb->common.cb() is
ide_dma_cb(), which will either create a new request, or find the
transfer to be done and call ide_set_inactive(), which clears
s->bus->dma->aiocb.  Therefore, the blk_drain() must wait for
ide_trim_bh_cb() to run, which currently it will not always do.

To fix this issue, we increment the BlockBackend's in-flight counter
when the TRIM operation begins (in ide_issue_trim(), when the
ide_trim_bh_cb() BH is created) and decrement it when ide_trim_bh_cb()
is done.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2029980
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220120142259.120189-1-hreitz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Tested-by: John Snow <jsnow@redhat.com>

Signed-off-by: tangbinzy <tangbin_yewu@cmss.chinamobile.com>
---
 hw/ide/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index e28f8aad61..15138225be 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -433,12 +433,16 @@ static const AIOCBInfo trim_aiocb_info = {
 static void ide_trim_bh_cb(void *opaque)
 {
     TrimAIOCB *iocb = opaque;
+    BlockBackend *blk = iocb->s->blk;
 
     iocb->common.cb(iocb->common.opaque, iocb->ret);
 
     qemu_bh_delete(iocb->bh);
     iocb->bh = NULL;
     qemu_aio_unref(iocb);
+
+    /* Paired with an increment in ide_issue_trim() */
+    blk_dec_in_flight(blk);
 }
 
 static void ide_issue_trim_cb(void *opaque, int ret)
@@ -508,6 +512,9 @@ BlockAIOCB *ide_issue_trim(
     IDEState *s = opaque;
     TrimAIOCB *iocb;
 
+    /* Paired with a decrement in ide_trim_bh_cb() */
+    blk_inc_in_flight(s->blk);
+
     iocb = blk_aio_get(&trim_aiocb_info, s->blk, cb, cb_opaque);
     iocb->s = s;
     iocb->bh = qemu_bh_new(ide_trim_bh_cb, iocb);
-- 
2.41.0.windows.1