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... > 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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