https://github.com/torvalds/linux
Revision 012a45e3f4af68e86d85cce060c6c2fed56498b2 authored by Leon Ma on 30 April 2014, 08:43:10 UTC, committed by Thomas Gleixner on 30 April 2014, 10:34:51 UTC
If a cpu is idle and starts an hrtimer which is not pinned on that same cpu, the nohz code might target the timer to a different cpu. In the case that we switch the cpu base of the timer we already have a sanity check in place, which determines whether the timer is earlier than the current leftmost timer on the target cpu. In that case we enqueue the timer on the current cpu because we cannot reprogram the clock event device on the target. If the timers base is already the target CPU we do not have this sanity check in place so we enqueue the timer as the leftmost timer in the target cpus rb tree, but we cannot reprogram the clock event device on the target cpu. So the timer expires late and subsequently prevents the reprogramming of the target cpu clock event device until the previously programmed event fires or a timer with an earlier expiry time gets enqueued on the target cpu itself. Add the same target check as we have for the switch base case and start the timer on the current cpu if it would become the leftmost timer on the target. [ tglx: Rewrote subject and changelog ] Signed-off-by: Leon Ma <xindong.ma@intel.com> Link: http://lkml.kernel.org/r/1398847391-5994-1-git-send-email-xindong.ma@intel.com Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1 parent 6c6c0d5
Tip revision: 012a45e3f4af68e86d85cce060c6c2fed56498b2 authored by Leon Ma on 30 April 2014, 08:43:10 UTC
hrtimer: Prevent remote enqueue of leftmost timers
hrtimer: Prevent remote enqueue of leftmost timers
Tip revision: 012a45e
highuid.txt
Notes on the change from 16-bit UIDs to 32-bit UIDs:
- kernel code MUST take into account __kernel_uid_t and __kernel_uid32_t
when communicating between user and kernel space in an ioctl or data
structure.
- kernel code should use uid_t and gid_t in kernel-private structures and
code.
What's left to be done for 32-bit UIDs on all Linux architectures:
- Disk quotas have an interesting limitation that is not related to the
maximum UID/GID. They are limited by the maximum file size on the
underlying filesystem, because quota records are written at offsets
corresponding to the UID in question.
Further investigation is needed to see if the quota system can cope
properly with huge UIDs. If it can deal with 64-bit file offsets on all
architectures, this should not be a problem.
- Decide whether or not to keep backwards compatibility with the system
accounting file, or if we should break it as the comments suggest
(currently, the old 16-bit UID and GID are still written to disk, and
part of the former pad space is used to store separate 32-bit UID and
GID)
- Need to validate that OS emulation calls the 16-bit UID
compatibility syscalls, if the OS being emulated used 16-bit UIDs, or
uses the 32-bit UID system calls properly otherwise.
This affects at least:
iBCS on Intel
sparc32 emulation on sparc64
(need to support whatever new 32-bit UID system calls are added to
sparc32)
- Validate that all filesystems behave properly.
At present, 32-bit UIDs _should_ work for:
ext2
ufs
isofs
nfs
coda
udf
Ioctl() fixups have been made for:
ncpfs
smbfs
Filesystems with simple fixups to prevent 16-bit UID wraparound:
minix
sysv
qnx4
Other filesystems have not been checked yet.
- The ncpfs and smpfs filesystems cannot presently use 32-bit UIDs in
all ioctl()s. Some new ioctl()s have been added with 32-bit UIDs, but
more are needed. (as well as new user<->kernel data structures)
- The ELF core dump format only supports 16-bit UIDs on arm, i386, m68k,
sh, and sparc32. Fixing this is probably not that important, but would
require adding a new ELF section.
- The ioctl()s used to control the in-kernel NFS server only support
16-bit UIDs on arm, i386, m68k, sh, and sparc32.
- make sure that the UID mapping feature of AX25 networking works properly
(it should be safe because it's always used a 32-bit integer to
communicate between user and kernel)
Chris Wing
wingc@umich.edu
last updated: January 11, 2000
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