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