Messages in this thread | | | Date | Thu, 22 Apr 2021 21:44:17 +0200 | From | Thomas Gleixner <> | Subject | [patch 0/6] futex: Bugfixes and FUTEX_LOCK_PI2 |
| |
The following series started off looking into supporting selectable clocks for FUTEX_LOCK_PI which is hardcoded to CLOCK_REALTIME and cannot be changed.
On the way I found two bugs related to the timeout handling:
- The allowance for FUTEX_WAIT to use FUTEX_CLOCK_REALTIME is broken and never worked.
- The recent time namespace support wreckaged FUTEX_LOCK_PI timeouts when the task belongs to a namespace which has an CLOCK_MONOTONIC offset.
Both should have been caught by that Gleixner dude when merging them, but it seems he's getting old.
Not having a selectable clock for PI futexes is inconsistent because all other interfaces have it. Unfortunately this was figured out by glibc folks quite some time ago, but nobody told us :(
The nasty hack to support it would be to treat FUTEX_CLOCK_REALTIME inverse for FUTEX_LOCK_PI, but that's a horrible idea. Adding a new flag to the futex op, i.e. FUTEX_CLOCK_MONOTONIC would be possible, but that's yet another variant which makes is harder for libraries to have a consistent clock selection handling.
So I went the way to let FUTEX_LOCK_PI alone and to add FUTEX_LOCK_PI2 which handles the clocks the same way as the other operands.
Thoughts?
The series is also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git futex
Thanks,
tglx --- include/uapi/linux/futex.h | 1 kernel/futex.c | 89 +++++++++++++++++++++++---------------------- 2 files changed, 47 insertions(+), 43 deletions(-)
| |