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Linux kernel source tree
de4da7bd5c
When you run a KVM guest with vhost-net and migrate that guest to
another host, and you immediately enable postcopy after starting the
migration, there is a big chance that the network connection of the
guest won't work anymore on the destination side after the migration.
With a debug kernel v6.16.0, there is also a call trace that looks
like this:
FAULT_FLAG_ALLOW_RETRY missing 881
CPU: 6 UID: 0 PID: 549 Comm: kworker/6:2 Kdump: loaded Not tainted 6.16.0 #56 NONE
Hardware name: IBM 3931 LA1 400 (LPAR)
Workqueue: events irqfd_inject [kvm]
Call Trace:
[<00003173cbecc634>] dump_stack_lvl+0x104/0x168
[<00003173cca69588>] handle_userfault+0xde8/0x1310
[<00003173cc756f0c>] handle_pte_fault+0x4fc/0x760
[<00003173cc759212>] __handle_mm_fault+0x452/0xa00
[<00003173cc7599ba>] handle_mm_fault+0x1fa/0x6a0
[<00003173cc73409a>] __get_user_pages+0x4aa/0xba0
[<00003173cc7349e8>] get_user_pages_remote+0x258/0x770
[<000031734be6f052>] get_map_page+0xe2/0x190 [kvm]
[<000031734be6f910>] adapter_indicators_set+0x50/0x4a0 [kvm]
[<000031734be7f674>] set_adapter_int+0xc4/0x170 [kvm]
[<000031734be2f268>] kvm_set_irq+0x228/0x3f0 [kvm]
[<000031734be27000>] irqfd_inject+0xd0/0x150 [kvm]
[<00003173cc00c9ec>] process_one_work+0x87c/0x1490
[<00003173cc00dda6>] worker_thread+0x7a6/0x1010
[<00003173cc02dc36>] kthread+0x3b6/0x710
[<00003173cbed2f0c>] __ret_from_fork+0xdc/0x7f0
[<00003173cdd737ca>] ret_from_fork+0xa/0x30
3 locks held by kworker/6:2/549:
#0: 00000000800bc958 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x7ee/0x1490
#1: 000030f3d527fbd0 ((work_completion)(&irqfd->inject)){+.+.}-{0:0}, at: process_one_work+0x81c/0x1490
#2: 00000000f99862b0 (&mm->mmap_lock){++++}-{3:3}, at: get_map_page+0xa8/0x190 [kvm]
The "FAULT_FLAG_ALLOW_RETRY missing" indicates that handle_userfaultfd()
saw a page fault request without ALLOW_RETRY flag set, hence userfaultfd
cannot remotely resolve it (because the caller was asking for an immediate
resolution, aka, FAULT_FLAG_NOWAIT, while remote faults can take time).
With that, get_map_page() failed and the irq was lost.
We should not be strictly in an atomic environment here and the worker
should be sleepable (the call is done during an ioctl from userspace),
so we can allow adapter_indicators_set() to just sleep waiting for the
remote fault instead.
Link: https://issues.redhat.com/browse/RHEL-42486
Signed-off-by: Peter Xu <peterx@redhat.com>
[thuth: Assembled patch description and fixed some cosmetical issues]
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.