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128 lines
4.3 KiB
128 lines
4.3 KiB
From 103608465b8bd2edf7f9aaef5c3c93309ccf9ec2 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Tue, 21 Feb 2023 16:22:17 -0500
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Subject: [PATCH 12/13] dma-helpers: prevent dma_blk_cb() vs dma_aio_cancel()
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race
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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RH-MergeRequest: 264: scsi: protect req->aiocb with AioContext lock
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RH-Bugzilla: 2090990
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RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Commit: [2/3] 14f5835093ba8c5111f3ada2fe87730371aca733
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dma_blk_cb() only takes the AioContext lock around ->io_func(). That
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means the rest of dma_blk_cb() is not protected. In particular, the
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DMAAIOCB field accesses happen outside the lock.
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There is a race when the main loop thread holds the AioContext lock and
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invokes scsi_device_purge_requests() -> bdrv_aio_cancel() ->
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dma_aio_cancel() while an IOThread executes dma_blk_cb(). The dbs->acb
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field determines how cancellation proceeds. If dma_aio_cancel() sees
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dbs->acb == NULL while dma_blk_cb() is still running, the request can be
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completed twice (-ECANCELED and the actual return value).
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The following assertion can occur with virtio-scsi when an IOThread is
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used:
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../hw/scsi/scsi-disk.c:368: scsi_dma_complete: Assertion `r->req.aiocb != NULL' failed.
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Fix the race by holding the AioContext across dma_blk_cb(). Now
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dma_aio_cancel() under the AioContext lock will not see
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inconsistent/intermediate states.
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Cc: Paolo Bonzini <pbonzini@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-Id: <20230221212218.1378734-3-stefanha@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit abfcd2760b3e70727bbc0792221b8b98a733dc32)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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hw/scsi/scsi-disk.c | 4 +---
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softmmu/dma-helpers.c | 12 +++++++-----
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2 files changed, 8 insertions(+), 8 deletions(-)
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diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
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index 179ce22c4a..c8109a673e 100644
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--- a/hw/scsi/scsi-disk.c
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+++ b/hw/scsi/scsi-disk.c
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@@ -351,13 +351,12 @@ done:
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scsi_req_unref(&r->req);
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}
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+/* Called with AioContext lock held */
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static void scsi_dma_complete(void *opaque, int ret)
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{
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SCSIDiskReq *r = (SCSIDiskReq *)opaque;
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SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
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- aio_context_acquire(blk_get_aio_context(s->qdev.conf.blk));
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-
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assert(r->req.aiocb != NULL);
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r->req.aiocb = NULL;
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@@ -367,7 +366,6 @@ static void scsi_dma_complete(void *opaque, int ret)
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block_acct_done(blk_get_stats(s->qdev.conf.blk), &r->acct);
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}
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scsi_dma_complete_noio(r, ret);
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- aio_context_release(blk_get_aio_context(s->qdev.conf.blk));
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}
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static void scsi_read_complete_noio(SCSIDiskReq *r, int ret)
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diff --git a/softmmu/dma-helpers.c b/softmmu/dma-helpers.c
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index 7d766a5e89..42af18719a 100644
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--- a/softmmu/dma-helpers.c
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+++ b/softmmu/dma-helpers.c
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@@ -127,17 +127,19 @@ static void dma_complete(DMAAIOCB *dbs, int ret)
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static void dma_blk_cb(void *opaque, int ret)
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{
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DMAAIOCB *dbs = (DMAAIOCB *)opaque;
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+ AioContext *ctx = dbs->ctx;
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dma_addr_t cur_addr, cur_len;
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void *mem;
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trace_dma_blk_cb(dbs, ret);
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+ aio_context_acquire(ctx);
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dbs->acb = NULL;
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dbs->offset += dbs->iov.size;
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if (dbs->sg_cur_index == dbs->sg->nsg || ret < 0) {
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dma_complete(dbs, ret);
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- return;
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+ goto out;
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}
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dma_blk_unmap(dbs);
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@@ -177,9 +179,9 @@ static void dma_blk_cb(void *opaque, int ret)
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if (dbs->iov.size == 0) {
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trace_dma_map_wait(dbs);
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- dbs->bh = aio_bh_new(dbs->ctx, reschedule_dma, dbs);
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+ dbs->bh = aio_bh_new(ctx, reschedule_dma, dbs);
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cpu_register_map_client(dbs->bh);
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- return;
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+ goto out;
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}
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if (!QEMU_IS_ALIGNED(dbs->iov.size, dbs->align)) {
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@@ -187,11 +189,11 @@ static void dma_blk_cb(void *opaque, int ret)
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QEMU_ALIGN_DOWN(dbs->iov.size, dbs->align));
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}
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- aio_context_acquire(dbs->ctx);
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dbs->acb = dbs->io_func(dbs->offset, &dbs->iov,
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dma_blk_cb, dbs, dbs->io_func_opaque);
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- aio_context_release(dbs->ctx);
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assert(dbs->acb);
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+out:
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+ aio_context_release(ctx);
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}
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static void dma_aio_cancel(BlockAIOCB *acb)
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--
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2.37.3
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