Am 09.06.2026 um 17:49 hat Stefan Hajnoczi geschrieben: > On Mon, Jun 08, 2026 at 02:17:46PM +0200, Kevin Wolf wrote: > > [Cc: Paolo, Stefan] > > > > Am 30.05.2026 um 19:58 hat Boudewijn van der Heide geschrieben: > > > scsi_disk_emulate_command() can be called from a coroutine; > > > when req->cmd.buf[0] is ALLOW_MEDIUM_REMOVAL, the synchronous > > > blk_lock_medium() is called, which hits assert(!qemu_in_coroutine()), > > > and crashes: > > > > > > qemu-system-hppa: block/block-gen.c:1692: blk_lock_medium: > > > Assertion `!qemu_in_coroutine()' failed. > > > > > > blk_eject() has the same problem, it can be called from coroutine, > > > because the same vtable entry (SCSIReqOps.send_command, > > > scsi_disk_emulate_command() here) calls blk_eject when req->cmd.buf[0] > > > is START_STOP. > > > > > > Fix by switching to co_wrapper_mixed for blk_lock_medium() and > > > blk_eject() instead of just co_wrapper. > > > > > > Signed-off-by: Boudewijn van der Heide <[email protected]> > > > > Yes, that will fix your immediate symptoms. I'm not completely sure if > > that's the level where we want to fix things, though, which is why I > > added Paolo and Stefan to Cc. > > > > > --- > > > Observed crash on fedora qemu-10.1.5-1.fc43 on x86_64 host using > > > qemu-system-hppa. > > > > > > trace: > > > > > > Thread 1 (...): > > > # 5 __assert_fail (...) at assert.c > > > # 6 blk_lock_medium (...) at block/block-gen.c > > > # 7 scsi_disk_emulate_command (...) at ../hw/scsi/scsi-disk.c > > > # 8 scsi_req_enqueue (...) at ../hw/scsi/scsi-bus.c > > > # 9 lsi_do_command (...) at ../hw/scsi/lsi53c895a.c > > > # 10 lsi_execute_script (...) at ../hw/scsi/lsi53c895a.c > > > # 11 scsi_read_complete_noio (...) at ../hw/scsi/scsi-disk.c > > > # 12 blk_aio_complete (...) at ../block/block-backend.c > > > # 14 blk_aio_read_entry (...) at ../block/block-backend.c > > > # 15 in coroutine_trampoline (...) at ../util/coroutine-ucontext.c > > > > > > blk_eject() has the same path, but req->cmd.buf[0] is START_STOP instead > > > of ALLOW_MEDIUM_REMOVAL inside scsi_disk_emulate_command(), > > > so fix that aswell. > > > > This would be useful information to have in the commit message proper. > > > > The step from #10 to #11 seems to be a rather big one that left out > > intermediate function calls, so I'm not sure if I fully understand it. > > > > Either way, I don't think lsi_execute_script() and the functions called > > by it were ever written with the intention to run in a coroutine. I'm > > almost sure that problems can be in more than just the two functions > > you're changing here. So my question is mostly, should the path involve > > a BH somewhere to break out of coroutine context, instead of making one > > or two specific cases work? > > The code path in this bug is from the block layer (blk_aio_read_entry -> > blk_aio_complete) to scsi-disk (scsi_read_complete_noio) into the LSI > device (probably lsi_command_complete -> lsi_resume_script -> > lsi_execute_script). > > I'm not sure if the LSI device, which is unaware of coroutines, should > have to work around this. It seems cleaner for blk_aio_preadv() to > invoke cb() from outside coroutine context since that API does not say > anything about coroutine contexts. > > On the other hand, there will be a performance overhead for leaving > coroutine context even when it would be fine to run in a coroutine...
Yes, I don't think it should be done by the block layer when most callbacks are just fine with running in a coroutine. I was thinking that maybe something in the SCSI layer should do it, or even scsi-disk specifically. Though of course, if virtio-scsi doesn't have the problem (does it?), taking the performance overhead for fixing LSI is probably also not what we want. Another, more radical solution, could be to move SCSI requests as a whole into coroutines, changing the assumption everywhere from no_coroutine_fn to coroutine_fn without bothering with mixed functions at all. The SCSI state machine is quite complex and I often find the control flow in the current callback-based code hard to understand, so I think this has the potential to improve the code, though of course it would also be a big change. Or, of course, we just take this patch, and keep fixing instances of the problem as they come up. Kevin > > If the general feeling is that we do want to make essentially all of the > > SCSI code coroutine_mixed_fn and are prepared to fix any issues arising > > from it, then this patch is fine as far as I am concerned. > > > > Kevin > > > > > --- > > > include/system/block-backend-io.h | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/system/block-backend-io.h > > > b/include/system/block-backend-io.h > > > index fd84723d9d..7368ad5c09 100644 > > > --- a/include/system/block-backend-io.h > > > +++ b/include/system/block-backend-io.h > > > @@ -81,10 +81,10 @@ bool coroutine_fn GRAPH_RDLOCK > > > blk_co_is_available(BlockBackend *blk); > > > bool co_wrapper_mixed_bdrv_rdlock blk_is_available(BlockBackend *blk); > > > > > > void coroutine_fn blk_co_lock_medium(BlockBackend *blk, bool locked); > > > -void co_wrapper blk_lock_medium(BlockBackend *blk, bool locked); > > > +void co_wrapper_mixed blk_lock_medium(BlockBackend *blk, bool locked); > > > > > > void coroutine_fn blk_co_eject(BlockBackend *blk, bool eject_flag); > > > -void co_wrapper blk_eject(BlockBackend *blk, bool eject_flag); > > > +void co_wrapper_mixed blk_eject(BlockBackend *blk, bool eject_flag); > > > > > > int64_t coroutine_fn blk_co_getlength(BlockBackend *blk); > > > int64_t co_wrapper_mixed blk_getlength(BlockBackend *blk); > > > -- > > > 2.54.0 > > > > >
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