Am 13.08.2018 um 10:32 hat Denis Plotnikov geschrieben: > Ping ping! > > On 16.07.2018 21:59, John Snow wrote: > > > > > > On 07/16/2018 11:01 AM, Denis Plotnikov wrote: > > > Ping! > > > > > > > I never saw a reply to Stefan's question on July 2nd, did you reply > > off-list? > > > > --js > Yes, I did. I talked to Stefan why the patch set appeared.
The rest of us still don't know the answer. I had the same question. Kevin > > > On 29.06.2018 15:40, Denis Plotnikov wrote: > > > > There are cases when a request to a block driver state shouldn't have > > > > appeared producing dangerous race conditions. > > > > This misbehaviour is usually happens with storage devices emulated > > > > without eventfd for guest to host notifications like IDE. > > > > > > > > The issue arises when the context is in the "drained" section > > > > and doesn't expect the request to come, but request comes from the > > > > device not using iothread and which context is processed by the main > > > > loop. > > > > > > > > The main loop apart of the iothread event loop isn't blocked by the > > > > "drained" section. > > > > The request coming and processing while in "drained" section can spoil > > > > the > > > > block driver state consistency. > > > > > > > > This behavior can be observed in the following KVM-based case: > > > > > > > > 1. Setup a VM with an IDE disk. > > > > 2. Inside a VM start a disk writing load for the IDE device > > > > e.g: dd if=<file> of=<file> bs=X count=Y oflag=direct > > > > 3. On the host create a mirroring block job for the IDE device > > > > e.g: drive_mirror <your_IDE> <your_path> > > > > 4. On the host finish the block job > > > > e.g: block_job_complete <your_IDE> > > > > Having done the 4th action, you could get an assert: > > > > assert(QLIST_EMPTY(&bs->tracked_requests)) from mirror_run. > > > > On my setup, the assert is 1/3 reproducible. > > > > > > > > The patch series introduces the mechanism to postpone the requests > > > > until the BDS leaves "drained" section for the devices not using > > > > iothreads. > > > > Also, it modifies the asynchronous block backend infrastructure to use > > > > that mechanism to release the assert bug for IDE devices. > > > > > > > > Denis Plotnikov (2): > > > > async: add infrastructure for postponed actions > > > > block: postpone the coroutine executing if the BDS's is drained > > > > > > > > block/block-backend.c | 58 ++++++++++++++++++++++++++++++--------- > > > > include/block/aio.h | 63 > > > > +++++++++++++++++++++++++++++++++++++++++++ > > > > util/async.c | 33 +++++++++++++++++++++++ > > > > 3 files changed, 142 insertions(+), 12 deletions(-) > > > > > > > > > -- > Best, > Denis
