82a8a30c58
There are currently two ways in which ublk server exit is detected by ublk_drv: 1. uring_cmd cancellation. If there are any outstanding uring_cmds which have not been completed to the ublk server when it exits, io_uring calls the uring_cmd callback with a special cancellation flag as the issuing task is exiting. 2. I/O timeout. This is needed in addition to the above to handle the "saturated queue" case, when all I/Os for a given queue are in the ublk server, and therefore there are no outstanding uring_cmds to cancel when the ublk server exits. There are a couple of issues with this approach: - It is complex and inelegant to have two methods to detect the same condition - The second method detects ublk server exit only after a long delay (~30s, the default timeout assigned by the block layer). This delays the nosrv behavior from kicking in and potential subsequent recovery of the device. The second issue is brought to light with the new test_generic_06 which will be added in following patch. It fails before this fix: selftests: ublk: test_generic_06.sh dev id is 0 dd: error writing '/dev/ublkb0': Input/output error 1+0 records in 0+0 records out 0 bytes copied, 30.0611 s, 0.0 kB/s DEAD dd took 31 seconds to exit (>= 5s tolerance)! generic_06 : [FAIL] Fix this by instead detecting and handling ublk server exit in the character file release callback. This has several advantages: - This one place can handle both saturated and unsaturated queues. Thus, it replaces both preexisting methods of detecting ublk server exit. - It runs quickly on ublk server exit - there is no 30s delay. - It starts the process of removing task references in ublk_drv. This is needed if we want to relax restrictions in the driver like letting only one thread serve each queue There is also the disadvantage that the character file release callback can also be triggered by intentional close of the file, which is a significant behavior change. Preexisting ublk servers (libublksrv) are dependent on the ability to open/close the file multiple times. To address this, only transition to a nosrv state if the file is released while the ublk device is live. This allows for programs to open/close the file multiple times during setup. It is still a behavior change if a ublk server decides to close/reopen the file while the device is LIVE (i.e. while it is responsible for serving I/O), but that would be highly unusual. This behavior is in line with what is done by FUSE, which is very similar to ublk in that a userspace daemon is providing services traditionally provided by the kernel. With this change in, the new test (and all other selftests, and all ublksrv tests) pass: selftests: ublk: test_generic_06.sh dev id is 0 dd: error writing '/dev/ublkb0': Input/output error 1+0 records in 0+0 records out 0 bytes copied, 0.0376731 s, 0.0 kB/s DEAD generic_04 : [PASS] Signed-off-by: Uday Shankar <ushankar@purestorage.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Link: https://lore.kernel.org/r/20250416035444.99569-6-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk> |
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.