Re: [Qemu-devel] [PATCH 1.1] scsi: Add assertion for use-after-free errors
Il 03/05/2012 22:58, Stefan Weil ha scritto: Am 03.05.2012 19:36, schrieb Stefan Weil: The QEMU emulation which is currently used with Raspberry PI images (qemu-system-arm -M versatilepb ...) accesses memory which was freed. Valgrind output (extract): ==17857== Invalid write of size 4 ==17857== at 0x24EB06: scsi_req_unref (scsi-bus.c:1273) ==17857== by 0x24FFAE: scsi_read_complete (scsi-disk.c:277) ==17857== by 0x152ACC: bdrv_co_em_bh (block.c:3363) ==17857== by 0x13D49C: qemu_bh_poll (async.c:71) ==17857== by 0x211A8C: main_loop_wait (main-loop.c:503) ==17857== by 0x207954: main_loop (vl.c:1555) ==17857== by 0x20E9C9: main (vl.c:3653) ==17857== Address 0x1c54383c is 12 bytes inside a block of size 260 free'd ==17857== at 0x4824B3A: free (vg_replace_malloc.c:366) ==17857== by 0x20ADFA: free_and_trace (vl.c:2250) ==17857== by 0x4899FC5: g_free (in /lib/libglib-2.0.so.0.2400.1) ==17857== by 0x24EB3B: scsi_req_unref (scsi-bus.c:1277) ==17857== by 0x24F003: scsi_req_complete (scsi-bus.c:1383) ==17857== by 0x25022A: scsi_read_data (scsi-disk.c:334) ==17857== by 0x24EB9F: scsi_req_continue (scsi-bus.c:1289) ==17857== by 0x1C7787: lsi_do_dma (lsi53c895a.c:575) ==17857== by 0x1C8CDA: lsi_execute_script (lsi53c895a.c:1147) ==17857== by 0x1C74EA: lsi_resume_script (lsi53c895a.c:510) ==17857== by 0x1C7ECD: lsi_transfer_data (lsi53c895a.c:746) ==17857== by 0x24EC90: scsi_req_data (scsi-bus.c:1307) Yes, this was reported by David Gibson too. Interesting that virtio-scsi doesn't show it, probably it's the sglist support that hides it. I queued the fix and I'm sending the pull request in a matter of minutes. The patch is a good addition so I queued it too, thanks. Paolo
[Qemu-devel] [PATCH 1.1] scsi: Add assertion for use-after-free errors
The QEMU emulation which is currently used with Raspberry PI images
(qemu-system-arm -M versatilepb ...) accesses memory which was freed.
Valgrind output (extract):
==17857== Invalid write of size 4
==17857==at 0x24EB06: scsi_req_unref (scsi-bus.c:1273)
==17857==by 0x24FFAE: scsi_read_complete (scsi-disk.c:277)
==17857==by 0x152ACC: bdrv_co_em_bh (block.c:3363)
==17857==by 0x13D49C: qemu_bh_poll (async.c:71)
==17857==by 0x211A8C: main_loop_wait (main-loop.c:503)
==17857==by 0x207954: main_loop (vl.c:1555)
==17857==by 0x20E9C9: main (vl.c:3653)
==17857== Address 0x1c54383c is 12 bytes inside a block of size 260 free'd
==17857==at 0x4824B3A: free (vg_replace_malloc.c:366)
==17857==by 0x20ADFA: free_and_trace (vl.c:2250)
==17857==by 0x4899FC5: g_free (in /lib/libglib-2.0.so.0.2400.1)
==17857==by 0x24EB3B: scsi_req_unref (scsi-bus.c:1277)
==17857==by 0x24F003: scsi_req_complete (scsi-bus.c:1383)
==17857==by 0x25022A: scsi_read_data (scsi-disk.c:334)
==17857==by 0x24EB9F: scsi_req_continue (scsi-bus.c:1289)
==17857==by 0x1C7787: lsi_do_dma (lsi53c895a.c:575)
==17857==by 0x1C8CDA: lsi_execute_script (lsi53c895a.c:1147)
==17857==by 0x1C74EA: lsi_resume_script (lsi53c895a.c:510)
==17857==by 0x1C7ECD: lsi_transfer_data (lsi53c895a.c:746)
==17857==by 0x24EC90: scsi_req_data (scsi-bus.c:1307)
(There are some more similar messages.)
This patch adds an assertion which also detects those errors:
Calling scsi_req_unref is not allowed when the previous call
of that function has decremented refcount to 0, because in this
case req was freed.
Signed-off-by: Stefan Weil s...@weilnetz.de
---
There are chances that this patch breaks some test scenarios,
but that is intentional: we should not pretend that there are
no errors when there are some.
The Raspberry PI emulation with QEMU is currently used by
a lot of people.
Please apply this patch for the tests of QEMU 1.1.
Of course we should also fix the problem which triggers the
assertion. I still don't know whether it is caused by
lsi53c895a.c or by the scsi code.
Thanks,
Stefan Weil
hw/scsi-bus.c |1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index dbdb99c..62779c7 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -1270,6 +1270,7 @@ SCSIRequest *scsi_req_ref(SCSIRequest *req)
void scsi_req_unref(SCSIRequest *req)
{
+assert(req-refcount 0);
if (--req-refcount == 0) {
if (req-ops-free_req) {
req-ops-free_req(req);
--
1.7.9
Re: [Qemu-devel] [PATCH 1.1] scsi: Add assertion for use-after-free errors
Am 03.05.2012 19:36, schrieb Stefan Weil: The QEMU emulation which is currently used with Raspberry PI images (qemu-system-arm -M versatilepb ...) accesses memory which was freed. Valgrind output (extract): ==17857== Invalid write of size 4 ==17857== at 0x24EB06: scsi_req_unref (scsi-bus.c:1273) ==17857== by 0x24FFAE: scsi_read_complete (scsi-disk.c:277) ==17857== by 0x152ACC: bdrv_co_em_bh (block.c:3363) ==17857== by 0x13D49C: qemu_bh_poll (async.c:71) ==17857== by 0x211A8C: main_loop_wait (main-loop.c:503) ==17857== by 0x207954: main_loop (vl.c:1555) ==17857== by 0x20E9C9: main (vl.c:3653) ==17857== Address 0x1c54383c is 12 bytes inside a block of size 260 free'd ==17857== at 0x4824B3A: free (vg_replace_malloc.c:366) ==17857== by 0x20ADFA: free_and_trace (vl.c:2250) ==17857== by 0x4899FC5: g_free (in /lib/libglib-2.0.so.0.2400.1) ==17857== by 0x24EB3B: scsi_req_unref (scsi-bus.c:1277) ==17857== by 0x24F003: scsi_req_complete (scsi-bus.c:1383) ==17857== by 0x25022A: scsi_read_data (scsi-disk.c:334) ==17857== by 0x24EB9F: scsi_req_continue (scsi-bus.c:1289) ==17857== by 0x1C7787: lsi_do_dma (lsi53c895a.c:575) ==17857== by 0x1C8CDA: lsi_execute_script (lsi53c895a.c:1147) ==17857== by 0x1C74EA: lsi_resume_script (lsi53c895a.c:510) ==17857== by 0x1C7ECD: lsi_transfer_data (lsi53c895a.c:746) ==17857== by 0x24EC90: scsi_req_data (scsi-bus.c:1307) Hi Paolo, this is the result of a bisect to narrow the source of problem: ac6684264642f1aea7cba5c0c3907409b1f7f904 is the first bad commit commit ac6684264642f1aea7cba5c0c3907409b1f7f904 Author: Paolo Bonzini pbonz...@redhat.com Date: Thu Apr 19 11:55:28 2012 +0200 scsi: support FUA on reads To force unit access on reads, flush the cache *before* doing the read. Signed-off-by: Paolo Bonzini pbonz...@redhat.com Regards, Stefan (There are some more similar messages.) This patch adds an assertion which also detects those errors: Calling scsi_req_unref is not allowed when the previous call of that function has decremented refcount to 0, because in this case req was freed. Signed-off-by: Stefan Weil s...@weilnetz.de --- There are chances that this patch breaks some test scenarios, but that is intentional: we should not pretend that there are no errors when there are some. The Raspberry PI emulation with QEMU is currently used by a lot of people. Please apply this patch for the tests of QEMU 1.1. Of course we should also fix the problem which triggers the assertion. I still don't know whether it is caused by lsi53c895a.c or by the scsi code. It is the scsi code, see git bisect result.
