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2efe41234d
syzbot reported the following ABBA deadlock:
CPU0 CPU1
---- ----
n_vclocks_store()
lock(&ptp->n_vclocks_mux) [1]
(physical clock)
pc_clock_adjtime()
lock(&clk->rwsem) [2]
(physical clock)
...
ptp_clock_freerun()
ptp_vclock_in_use()
lock(&ptp->n_vclocks_mux) [3]
(physical clock)
ptp_clock_unregister()
posix_clock_unregister()
lock(&clk->rwsem) [4]
(virtual clock)
Since ptp virtual clock is registered only under ptp physical clock, both
ptp_clock and posix_clock must be physical clocks for ptp_vclock_in_use()
to lock &ptp->n_vclocks_mux and check ptp->n_vclocks.
However, when unregistering vclocks in n_vclocks_store(), the locking
ptp->n_vclocks_mux is a physical clock lock, but clk->rwsem of
ptp_clock_unregister() called through device_for_each_child_reverse()
is a virtual clock lock.
Therefore, clk->rwsem used in CPU0 and clk->rwsem used in CPU1 are
different locks, but in lockdep, a false positive occurs because the
possibility of deadlock is determined through lock-class.
To solve this, lock subclass annotation must be added to the posix_clock
rwsem of the vclock.
Reported-by: syzbot+7cfb66a237c4a5fb22ad@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7cfb66a237c4a5fb22ad
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.