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add patch to avoid potential deadlock with trim for IDE/SATA and draining

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In particular, the deadlock can occur, together with unlucky timing
between the QEMU threads, when the guest is issuing trim requests
during the start of a backup operation.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
 [ T: resolve trivial merge conflict in series file ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
This commit is contained in:
Fiona Ebner 2023-03-08 12:51:05 +01:00 committed by Thomas Lamprecht
parent 10691e04e9
commit 58659169de
2 changed files with 79 additions and 0 deletions
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78
debian/patches/extra/0011-ide-avoid-potential-deadlock-when-draining-during-tr.patch vendored Normal file
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@ -0,0 +1,78 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Fiona Ebner <f.ebner@proxmox.com>
Date: Tue, 7 Mar 2023 15:03:02 +0100
Subject: [PATCH] ide: avoid potential deadlock when draining during trim
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The deadlock can happen as follows:
1. ide_issue_trim is called, and increments the in_flight counter.
2. ide_issue_trim_cb calls blk_aio_pdiscard.
3. Somebody else starts draining (e.g. backup to insert the cbw node).
4. ide_issue_trim_cb is called as the completion callback for
blk_aio_pdiscard.
5. ide_issue_trim_cb issues yet another blk_aio_pdiscard request.
6. The request is added to the wait queue via blk_wait_while_drained,
because draining has been started.
7. Nobody ever decrements the in_flight counter and draining can't
finish. This would be done by ide_trim_bh_cb, which is called after
ide_issue_trim_cb has issued its last request, but
ide_issue_trim_cb is not called anymore, because it's the
completion callback of blk_aio_pdiscard, which waits on draining.
Quoting Hanna Czenczek:
> The point of 7e5cdb345f was that we need any in-flight count to
> accompany a set s->bus->dma->aiocb. While blk_aio_pdiscard() is
> happening, we don’t necessarily need another count. But we do need
> it while there is no blk_aio_pdiscard().
> ide_issue_trim_cb() returns in two cases (and, recursively through
> its callers, leaves s->bus->dma->aiocb set):
> 1. After calling blk_aio_pdiscard(), which will keep an in-flight
> count,
> 2. After calling replay_bh_schedule_event() (i.e.
> qemu_bh_schedule()), which does not keep an in-flight count.
Thus, even after moving the blk_inc_in_flight to above the
replay_bh_schedule_event call, the invariant "ide_issue_trim_cb
returns with an accompanying in-flight count" is still satisfied.
Fixes: 7e5cdb345f ("ide: Increment BB in-flight counter for TRIM BH")
Suggested-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
hw/ide/core.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/hw/ide/core.c b/hw/ide/core.c
index 39afdc0006..6474522bc9 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -443,7 +443,7 @@ static void ide_trim_bh_cb(void *opaque)
iocb->bh = NULL;
qemu_aio_unref(iocb);
- /* Paired with an increment in ide_issue_trim() */
+ /* Paired with an increment in ide_issue_trim_cb() */
blk_dec_in_flight(blk);
}
@@ -503,6 +503,8 @@ static void ide_issue_trim_cb(void *opaque, int ret)
done:
iocb->aiocb = NULL;
if (iocb->bh) {
+ /* Paired with a decrement in ide_trim_bh_cb() */
+ blk_inc_in_flight(s->blk);
replay_bh_schedule_event(iocb->bh);
}
}
@@ -514,9 +516,6 @@ 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);

1
debian/patches/series vendored
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@ -8,6 +8,7 @@ extra/0007-block-fix-detect-zeroes-with-BDRV_REQ_REGISTERED_BUF.patch
extra/0008-memory-prevent-dma-reentracy-issues.patch
extra/0009-block-iscsi-fix-double-free-on-BUSY-or-similar-statu.patch
extra/0010-scsi-megasas-Internal-cdbs-have-16-byte-length.patch
extra/0011-ide-avoid-potential-deadlock-when-draining-during-tr.patch
bitmap-mirror/0001-drive-mirror-add-support-for-sync-bitmap-mode-never.patch
bitmap-mirror/0002-drive-mirror-add-support-for-conditional-and-always-.patch
bitmap-mirror/0003-mirror-add-check-for-bitmap-mode-without-bitmap.patch