On 21/7/26 12:21, Thomas Huth wrote:
On 21/07/2026 11.58, Philippe Mathieu-Daudé wrote:
On 21/7/26 11:51, Philippe Mathieu-Daudé wrote:
On 21/7/26 10:29, Mark Cave-Ayland wrote:
On 21/07/2026 08:02, Thomas Huth wrote:
From: Thomas Huth <[email protected]>
ide_cancel_dma_sync() is called with a "IDEState *s" for one of the
two IDE drives on a bus (primary or secondary drive) to cancel all
pending DMA transfers on the drive. The code then checks
s->bus->dma->aiocb to see whether there is any IO in flight on the
*bus* and then calls blk_drain(s->blk) to wait for its completion.
However, s->bus->dma->aiocb might belong to the other drive on the
bus, and if there is no disk attached to the current drive, s->blk
is NULL. Since blk_drain() does not check its parameter for a NULL
pointer, QEMU can crash in such a case.
To fix the problem, we have to check that "blk" is not NULL before
calling blk_drain(). And we have to call blk_drain() for both drives,
otherwise the assert(s->bus->dma->aiocb == NULL) statement after
the blk_drain() might trigger if the IO in flight belongs to the
the other drive.
Resolves: https://urldefense.proofpoint.com/v2/url?
u=https-3A__gitlab.com_qemu-2Dproject_qemu_-2D_work-5Fitems_905&d=DwIDAg&c=s883GpUCOChKOHiocYtGcg&r=c23RpsaH4D2MKyD3EPJTDa0BAxz6tV8aUJqVSoytEiY&m=BbZFP82dEZMyWzN5GnJ9XaxwmyrmYGbqWbEBNSUM_afB5JRRF3InIaZAr5UpUUh2&s=rCgSz13wVfk11Z-Uw5WTQViAQKkSvwpQqf_dJX1tiro&e=
Reported-by: Alexander Bulekov <[email protected]>
Resolves: https://urldefense.proofpoint.com/v2/url?
u=https-3A__gitlab.com_qemu-2Dproject_qemu_-2D_work-5Fitems_4052&d=DwIDAg&c=s883GpUCOChKOHiocYtGcg&r=c23RpsaH4D2MKyD3EPJTDa0BAxz6tV8aUJqVSoytEiY&m=BbZFP82dEZMyWzN5GnJ9XaxwmyrmYGbqWbEBNSUM_afB5JRRF3InIaZAr5UpUUh2&s=B-AkqMAsQwA0LzU5ptwPJ3ZIBAA8ncf5ZbQg8GTwaME&e=
Reported-by: dong ling
Signed-off-by: Thomas Huth <[email protected]>
---
v2: Drain both drives
hw/ide/core.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/hw/ide/core.c b/hw/ide/core.c
index f78b00220b8..f43ab95b07b 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -741,10 +741,17 @@ void ide_cancel_dma_sync(IDEState *s)
* In the future we'll be able to safely cancel the I/O if the
* whole DMA operation will be submitted to disk with a single
* aio operation with preadv/pwritev.
+ *
+ * Note: s->bus->dma->aiocb might belong to the adjacent
IDEState,
+ * so we have to drain both drives to get it cleared.
*/
if (s->bus->dma->aiocb) {
trace_ide_cancel_dma_sync_remaining();
- blk_drain(s->blk);
+ for (int i = 0; i < 2; i++) {
+ if (s->bus->ifs[i].blk) {
+ blk_drain(s->bus->ifs[i].blk);
+ }
+ }
assert(s->bus->dma->aiocb == NULL);
}
}
Doesn't ide_bus_active_if() do the right thing here for in-flight
requests?
bmdma_cmd_writeb() already calls ide_bus_active_if().
Is the issue in the caller, bmdma_cmd_writeb(), instead of
here in ide_cancel_dma_sync()?
i.e.:
-- >8 --
diff --git a/hw/ide/pci.c b/hw/ide/pci.c
index 7ce1ae67ab2..e7c6af9a49e 100644
--- a/hw/ide/pci.c
+++ b/hw/ide/pci.c
@@ -384,7 +384,7 @@ void bmdma_cmd_writeb(BMDMAState *bm, uint32_t val)
/* Ignore writes to SSBM if it keeps the old value */
if ((val & BM_CMD_START) != (bm->cmd & BM_CMD_START)) {
if (!(val & BM_CMD_START)) {
- ide_cancel_dma_sync(ide_bus_active_if(bm->bus));
+ ide_cancel_dma_sync(bmdma_active_if(bm));
bm->status &= ~BM_STATUS_DMAING;
} else {
bm->cur_addr = bm->addr;
No, I don't think this will fix all cases. While https://gitlab.com/
qemu-project/qemu/-/work_items/905 has a call trace with
bmdma_cmd_writeb() in it, https://gitlab.com/qemu-project/qemu/-/
work_items/4052 is slightly different: The backtrace shows
ide_bus_perform_srst() -> ide_perform_srst() -> ide_cancel_dma_sync()
here instead. I'd say let's play safe and always drain both interfaces.
WDYT?
I dunno I'm kind of lost. Can't blk_bs() handle NULL blk?
-- >8 --
diff --git a/block/block-backend.c b/block/block-backend.c
index 37ba7e9fc40..b5d84c9789a 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -760,7 +760,7 @@ BlockBackend *blk_by_name(const char *name)
BlockDriverState *blk_bs(BlockBackend *blk)
{
IO_CODE();
- return blk->root ? blk->root->bs : NULL;
+ return (blk && blk->root) ? blk->root->bs : NULL;
}
---
