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The following patch fixes two spots in the SN kernel
that check a fixed prom revision number to determine prom
feature support. These checks are only valid on shub1 systems.
They are invalid on shub2 systems which have a different prom
with different revision numbers.
Signed-off-by: Aaron Young <ayoung@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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Montecito is coming with dual core and threading, so this
four socket box can now have sixteen logical cpus.
Signed-off-by: Tony Luck <tony.luck@intel.com>
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Pass the OS logical cpu number to the PROM. This allows PROM
to log the OS logical cpu number in error records viewed thru POD.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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Chandra Seetharaman missed one place in commit:
65edc68c345cbe21d0b0375c3452a3ed5e322868
[but it only shows up when building the ski simulator configuration
of ia64, so thats understandable]
Signed-off-by: Tony Luck <tony.luck@intel.com>
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master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6
* 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6:
[netdrvr] Remove long-unused bits from Becker template drivers
[netdrvr] natsemi: minor cleanups
[netdrvr] natsemi: Separate out media initialization code
[PATCH] WAN: update info page for a bunch of my drivers
[PATCH] drivers/net/hamradio/dmascc.c: fix section mismatch
[PATCH] Fix phy id for LXT971A/LXT972A
[PATCH] DM9000 - minor code cleanups
[PATCH] DM9000 - do no re-init spin lock
[PATCH] DM9000 - check for MAC left in by bootloader
[PATCH] DM9000 - better checks for platform resources
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* git://git.infradead.org/mtd-2.6:
[MTD] NAND: Select chip before checking write protect status
[MTD] CORE mtdchar.c: fix off-by-one error in lseek()
[MTD] NAND: Fix typo in mtd/nand/ts7250.c
[JFFS2][XATTR] coexistence between xattr and write buffering support.
[JFFS2][XATTR] Fix wrong copyright
[JFFS2][XATTR] Re-define xd->refcnt as atomic_t
[JFFS2][XATTR] Fix memory leak with jffs2_xattr_ref
[JFFS2][XATTR] rid unnecessary writing of delete marker.
[JFFS2][XATTR] Fix ACL bug when updating null xattr by null ACL.
[JFFS2][XATTR] using 'delete marker' for xdatum/xref deletion
[MTD] Fix off-by-one error in physmap.c
[MTD] Remove unused 'nr_banks' variable from ixp2000 map driver
[MTD NAND] s3c2412 support in s3c2410.c
[MTD] Initialize 'writesize'
[MTD] NAND: ndfc fix address offset thinko
[MTD] NAND: S3C2410 convert prinks to dev_*()s
[MTD] NAND: Missing fixups
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* git://oss.sgi.com:8090/nathans/xfs-2.6:
[XFS] Fixup whitespace damage in log_write, remove final warning.
[XFS] Rework code snippets slightly to remove remaining recent-gcc
[XFS] Fix realtime subvolume expansion, a porting bug b0rked it. Coverity
[XFS] Remove a race condition where a linked inode could BUG_ON in
[XFS] Remove redundant directory checks from inode link operation.
[XFS] Remove a couple of no-longer-used macros.
[XFS] Reduce size of xfs_trans_t structure. * remove ->t_forw, ->t_back --
[XFS] remove unused behaviour lock - shrink XFS vnode as a side effect.
[XFS] * There is trivial "inode => vnode => inode" conversion, but only
[XFS] link(2) on directory is banned in VFS.
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master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev
* 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev:
[PATCH] ata_piix: add ICH6/7/8 to Kconfig
[PATCH] sata_sil: disable hotplug interrupts on two ATI IXPs
[PATCH] libata: cosmetic updates
[PATCH] ata: add some NVIDIA chipset IDs
[PATCH] libata reduce timeouts
[PATCH] libata: implement ata_port_max_devices()
[PATCH] libata: make two functions global
[PATCH] libata: update ata_do_simple_cmd()
[PATCH] libata: move ata_do_simple_cmd() below ata_exec_internal()
[PATCH] libata: clear EH action on device detach
[PATCH] libata: implement and use ata_deh_dev_action()
[PATCH] libata: move ata_eh_clear_action() upward
[PATCH] libata.h needs scatterlist.h
[libata] sata_vsc: partially revert a PCI ID-related commit
[libata] Bump versions
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The previous "delete" had actually just truncated it to a zero
size, something that can easily happen if you just apply a patch.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Commit 02dd7ae2892e5ceff111d032769c78d3377df970 ("[PATCH] i2c-i801:
Merge setup function") has a missing return 0 in the _probe() function.
This means the error path is always executed and pci_disable_device() is
called even when the device just got successfully enabled.
Having the SMBus device disabled makes some systems (eg.
Fujitsu-Siemens Lifebook E8010) hang hard during power-off.
Intead of reverting the whole commit this patch fixes it up:
- don't ever call pci_disable_device(), also not in the _remove() function
to avoid hangs
- fix missing pci_release_region() in error path
Signed-off-by: Daniel Ritz <daniel.ritz@gmx.ch>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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* git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6: (25 commits)
[CIFS] Fix authentication choice so we do not force NTLMv2 unless the
[CIFS] Fix alignment of unicode strings in previous patch
[CIFS] Fix allocation of buffers for new session setup routine to allow
[CIFS] Remove calls to to take f_owner.lock
[CIFS] remove some redundant null pointer checks
[CIFS] Fix compile warning when CONFIG_CIFS_EXPERIMENTAL is off
[CIFS] Enable sec flags on mount for cifs (part one)
[CIFS] Fix suspend/resume problem which causes EIO on subsequent access to
[CIFS] fix minor compile warning when config_cifs_weak_security is off
[CIFS] NTLMv2 support part 5
[CIFS] Add support for readdir to legacy servers
[CIFS] NTLMv2 support part 4
[CIFS] NTLMv2 support part 3
[CIFS] NTLMv2 support part 2
[CIFS] Fix mask so can set new cifs security flags properly
CIFS] Support for older servers which require plaintext passwords - part 2
[CIFS] Support for older servers which require plaintext passwords
[CIFS] Fix mapping of old SMB return code Invalid Net Name so it is
[CIFS] Missing brace
[CIFS] Do not overwrite aops
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Switch to using the new RAM Kconfig settings, instead of linker defined
regions in ROM specific 68328 startup code.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Switch to using the new RAM Kconfig settings, instead of linker defined
regions in ROM specific 68360 startup code.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Switch to using the new RAM Kconfig settings, instead of linker defined
regions in RAM specific 68360 startup code.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove NO_FORMAT_VEC conditional check. It is not used or defined anywhere.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Collection of fixes for the ColdFire FEC ethernet driver:
. reworked event setting so that it occurs after the MII setup.
roucaries bastien <roucaries.bastien@gmail.com>
. Do not read cbd_sc in memory for each bit we test. Once per buffer is enough.
. Overrun errors must increase `rx_fifo_errors', not `rx_crc_errors'
. No need for a special value to activate rx or tx. Only write access matters.
. Simplify parameter of eth_copy_and_sum : `data' has already the right value.
. Some spelling fixes.
Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Set different irq priority levels for each IRQ requested.
According to the Freescale ColdFire documentation each separate IRQ
must have its own unique priority/level combination.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add support for the FEC module in the ColdFire 532x CPU family.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Avoid requesting a `Graceful Transmit Stop' when link has disappeared,
because that request cannot complete without link.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Updated defconfig for m68knommu arch. Includes recent changes to the clock
and RAM configuration options.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add build support for the M523x ColdFire CPU family.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add support for the Avnet/5282 board.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Here is a small patch that made my kernel .text segment shrink by 8k IIRC
on my 5272-based board, by removing `-Wa,-S' from CFLAGS.
The `-Wa,-S' option prevents `gas' from using short forms of jsr.
Without it, `gas' replaces `jsr xxx.l' (6 bytes) by `jsr xxx@pc'
(4 bytes) when possible. On 5272, both forms are equally fast.
The `-Wa,-m5307' option is useless, because gcc already gives it
to `gas' from the `-m5307' option.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Voyager stopped booting some time in the 2.6.16-2.6.17 timeframe;
the reason was that it doesn't have a cpu_present_map, so add
one.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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* master.kernel.org:/pub/scm/linux/kernel/git/mchehab/v4l-dvb: (26 commits)
V4L/DVB (4263): Fix warning when compiling on 64 bit machines
V4L/DVB (4261): Included required header for in-kernel compilation
V4L/DVB (4260): Stradis.c: make 2 functions static
V4L/DVB (4259): Pass an explicit log prefix to cx2341x_log_status
V4L/DVB (4257): Fix 64-bit compile warnings.
V4L/DVB (4255): Tda9887 default TOP value is 0x10
V4L/DVB (4254): Remove obsoleted tuner_debug option.
V4L/DVB (4253): IVTV VBI format description too long.
V4L/DVB (4252): Remove duplicate 'tda9887' in info messages.
V4L/DVB (4245): Reduce the amount of pvrusb2-sourced noise going into the system log
V4L/DVB (4244): Implement use of cx2341x module in pvrusb2 driver
V4L/DVB (4243): Exploit new V4L control features in pvrusb2
V4L/DVB (4242): Don't suspend encoder when changing its attributes (in pvrusb2)
V4L/DVB (4241): Fix faulty encoder error recovery in pvrusb2
V4L/DVB (4240): Various V4L control enhancements in pvrusb2
V4L/DVB (4239): Handle boolean controls in pvrusb2
V4L/DVB (4238): Make sure flags field is initialized when quering a control in pvrusb2
V4L/DVB (4237): Move LOG_STATUS bracketing to a different part of the pvrusb2 driver
V4L/DVB (4236): Rearrange things in pvrusb2 driver in preparation for using cx2341x module
V4L/DVB (4235): Increase the maximum number of controls that pvrusb2-sysfs.c can handle.
...
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SGI-PV: 904196
SGI-Modid: xfs-linux-melb:xfs-kern:26366a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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DLE masking was non-functional since the new tty handling.
Found by Peter Evertz <leo2@pec.homeip.net>
Signed-off-by: Karsten Keil <kkeil@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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arch/i386/kernel/irq.c: In function 'do_IRQ':
arch/i386/kernel/irq.c:104: warning: suggest parentheses around arithmetic in operand of |
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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It's available in a header as a static inline - there's no need to export it.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Markus Lidel <Markus.Lidel@shadowconnect.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Make struct proc_ipmi_root static.
Besides this, tremove removes an unused #ifdef CONFIG_PROC_FS from
include/linux/ipmi.h.
Acked-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove redundant NULL chck before kfree + tiny CodingStyle cleanup for
drivers/
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove redundant kfree NULL checks from kernel/
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove redundant NULL checks before kfree for fs/
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Acked-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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In futex_requeue(), when the 2 futexes keys hash to the same bucket, there
is no need to move the futex_q to the end of the bucket list.
Signed-off-by: Sebastien Dugue <sebastien.dugue@bull.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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When the priority of a task, which is blocked on a lock, changes we must
propagate this change into the PI lock chain. Therefor the chain walk code
is changed to get rid of the references to current to avoid false positives
in the deadlock detector, as setscheduler might be called by a task which
holds the lock on which the task whose priority is changed is blocked.
Also add some comments about the get/put_task_struct usage to avoid
confusion.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Make test suite setscheduler calls asynchronously. Remove the waits in the
test cases and add a new testcase to verify the correctness of the
setscheduler priority propagation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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There is no need to hold tasklist_lock across the setscheduler call, when
we pin the task structure with get_task_struct(). Interrupts are disabled
in setscheduler anyway and the permission checks do not need interrupts
disabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Fix defaults and dependencies.
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This adds the actual pi-futex implementation, based on rt-mutexes.
[dino@in.ibm.com: fix an oops-causing race]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add proxy-locking rt-mutex functionality needed by pi-futexes.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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RT-mutex tester: scriptable tester for rt mutexes, which allows userspace
scripting of mutex unit-tests (and dynamic tests as well), using the actual
rt-mutex implementation of the kernel.
[akpm@osdl.org: fixlet]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Runtime debugging functionality for rt-mutexes.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add rt-mutex documentation.
[rostedt@goodmis.org: Update rt-mutex-design.txt as per Randy Dunlap suggestions]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Core functions for the rt-mutex subsystem.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add framework to boost/unboost the priority of RT tasks.
This consists of:
- caching the 'normal' priority in ->normal_prio
- providing a functions to set/get the priority of the task
- make sched_setscheduler() aware of boosting
The effective_prio() cleanups also fix a priority-calculation bug pointed out
by Andrey Gelman, in set_user_nice().
has_rt_policy() fix: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andrey Gelman <agelman@012.net.il>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add the priority-sorted list (plist) implementation.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Introduce a new WARN_ON variant: WARN_ON_SMP(cond).
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add debug_check_no_locks_freed(), as a central inline to add
bad-lock-free-debugging functionality to.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Fix typo in Documentation/robust-futexes.txt.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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We are pleased to announce "lightweight userspace priority inheritance" (PI)
support for futexes. The following patchset and glibc patch implements it,
ontop of the robust-futexes patchset which is included in 2.6.16-mm1.
We are calling it lightweight for 3 reasons:
- in the user-space fastpath a PI-enabled futex involves no kernel work
(or any other PI complexity) at all. No registration, no extra kernel
calls - just pure fast atomic ops in userspace.
- in the slowpath (in the lock-contention case), the system call and
scheduling pattern is in fact better than that of normal futexes, due to
the 'integrated' nature of FUTEX_LOCK_PI. [more about that further down]
- the in-kernel PI implementation is streamlined around the mutex
abstraction, with strict rules that keep the implementation relatively
simple: only a single owner may own a lock (i.e. no read-write lock
support), only the owner may unlock a lock, no recursive locking, etc.
Priority Inheritance - why, oh why???
-------------------------------------
Many of you heard the horror stories about the evil PI code circling Linux for
years, which makes no real sense at all and is only used by buggy applications
and which has horrible overhead. Some of you have dreaded this very moment,
when someone actually submits working PI code ;-)
So why would we like to see PI support for futexes?
We'd like to see it done purely for technological reasons. We dont think it's
a buggy concept, we think it's useful functionality to offer to applications,
which functionality cannot be achieved in other ways. We also think it's the
right thing to do, and we think we've got the right arguments and the right
numbers to prove that. We also believe that we can address all the
counter-arguments as well. For these reasons (and the reasons outlined below)
we are submitting this patch-set for upstream kernel inclusion.
What are the benefits of PI?
The short reply:
----------------
User-space PI helps achieving/improving determinism for user-space
applications. In the best-case, it can help achieve determinism and
well-bound latencies. Even in the worst-case, PI will improve the statistical
distribution of locking related application delays.
The longer reply:
-----------------
Firstly, sharing locks between multiple tasks is a common programming
technique that often cannot be replaced with lockless algorithms. As we can
see it in the kernel [which is a quite complex program in itself], lockless
structures are rather the exception than the norm - the current ratio of
lockless vs. locky code for shared data structures is somewhere between 1:10
and 1:100. Lockless is hard, and the complexity of lockless algorithms often
endangers to ability to do robust reviews of said code. I.e. critical RT
apps often choose lock structures to protect critical data structures, instead
of lockless algorithms. Furthermore, there are cases (like shared hardware,
or other resource limits) where lockless access is mathematically impossible.
Media players (such as Jack) are an example of reasonable application design
with multiple tasks (with multiple priority levels) sharing short-held locks:
for example, a highprio audio playback thread is combined with medium-prio
construct-audio-data threads and low-prio display-colory-stuff threads. Add
video and decoding to the mix and we've got even more priority levels.
So once we accept that synchronization objects (locks) are an unavoidable fact
of life, and once we accept that multi-task userspace apps have a very fair
expectation of being able to use locks, we've got to think about how to offer
the option of a deterministic locking implementation to user-space.
Most of the technical counter-arguments against doing priority inheritance
only apply to kernel-space locks. But user-space locks are different, there
we cannot disable interrupts or make the task non-preemptible in a critical
section, so the 'use spinlocks' argument does not apply (user-space spinlocks
have the same priority inversion problems as other user-space locking
constructs). Fact is, pretty much the only technique that currently enables
good determinism for userspace locks (such as futex-based pthread mutexes) is
priority inheritance:
Currently (without PI), if a high-prio and a low-prio task shares a lock [this
is a quite common scenario for most non-trivial RT applications], even if all
critical sections are coded carefully to be deterministic (i.e. all critical
sections are short in duration and only execute a limited number of
instructions), the kernel cannot guarantee any deterministic execution of the
high-prio task: any medium-priority task could preempt the low-prio task while
it holds the shared lock and executes the critical section, and could delay it
indefinitely.
Implementation:
---------------
As mentioned before, the userspace fastpath of PI-enabled pthread mutexes
involves no kernel work at all - they behave quite similarly to normal
futex-based locks: a 0 value means unlocked, and a value==TID means locked.
(This is the same method as used by list-based robust futexes.) Userspace uses
atomic ops to lock/unlock these mutexes without entering the kernel.
To handle the slowpath, we have added two new futex ops:
FUTEX_LOCK_PI
FUTEX_UNLOCK_PI
If the lock-acquire fastpath fails, [i.e. an atomic transition from 0 to TID
fails], then FUTEX_LOCK_PI is called. The kernel does all the remaining work:
if there is no futex-queue attached to the futex address yet then the code
looks up the task that owns the futex [it has put its own TID into the futex
value], and attaches a 'PI state' structure to the futex-queue. The pi_state
includes an rt-mutex, which is a PI-aware, kernel-based synchronization
object. The 'other' task is made the owner of the rt-mutex, and the
FUTEX_WAITERS bit is atomically set in the futex value. Then this task tries
to lock the rt-mutex, on which it blocks. Once it returns, it has the mutex
acquired, and it sets the futex value to its own TID and returns. Userspace
has no other work to perform - it now owns the lock, and futex value contains
FUTEX_WAITERS|TID.
If the unlock side fastpath succeeds, [i.e. userspace manages to do a TID ->
0 atomic transition of the futex value], then no kernel work is triggered.
If the unlock fastpath fails (because the FUTEX_WAITERS bit is set), then
FUTEX_UNLOCK_PI is called, and the kernel unlocks the futex on the behalf of
userspace - and it also unlocks the attached pi_state->rt_mutex and thus wakes
up any potential waiters.
Note that under this approach, contrary to other PI-futex approaches, there is
no prior 'registration' of a PI-futex. [which is not quite possible anyway,
due to existing ABI properties of pthread mutexes.]
Also, under this scheme, 'robustness' and 'PI' are two orthogonal properties
of futexes, and all four combinations are possible: futex, robust-futex,
PI-futex, robust+PI-futex.
glibc support:
--------------
Ulrich Drepper and Jakub Jelinek have written glibc support for PI-futexes
(and robust futexes), enabling robust and PI (PTHREAD_PRIO_INHERIT) POSIX
mutexes. (PTHREAD_PRIO_PROTECT support will be added later on too, no
additional kernel changes are needed for that). [NOTE: The glibc patch is
obviously inofficial and unsupported without matching upstream kernel
functionality.]
the patch-queue and the glibc patch can also be downloaded from:
http://redhat.com/~mingo/PI-futex-patches/
Many thanks go to the people who helped us create this kernel feature: Steven
Rostedt, Esben Nielsen, Benedikt Spranger, Daniel Walker, John Cooper, Arjan
van de Ven, Oleg Nesterov and others. Credits for related prior projects goes
to Dirk Grambow, Inaky Perez-Gonzalez, Bill Huey and many others.
Clean up the futex code, before adding more features to it:
- use u32 as the futex field type - that's the ABI
- use __user and pointers to u32 instead of unsigned long
- code style / comment style cleanups
- rename hash-bucket name from 'bh' to 'hb'.
I checked the pre and post futex.o object files to make sure this
patch has no code effects.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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