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* arch: Add lightweight memory barriers dma_rmb() and dma_wmb()Alexander Duyck2014-12-121-0/+42
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There are a number of situations where the mandatory barriers rmb() and wmb() are used to order memory/memory operations in the device drivers and those barriers are much heavier than they actually need to be. For example in the case of PowerPC wmb() calls the heavy-weight sync instruction when for coherent memory operations all that is really needed is an lsync or eieio instruction. This commit adds a coherent only version of the mandatory memory barriers rmb() and wmb(). In most cases this should result in the barrier being the same as the SMP barriers for the SMP case, however in some cases we use a barrier that is somewhere in between rmb() and smp_rmb(). For example on ARM the rmb barriers break down as follows: Barrier Call Explanation --------- -------- ---------------------------------- rmb() dsb() Data synchronization barrier - system dma_rmb() dmb(osh) data memory barrier - outer sharable smp_rmb() dmb(ish) data memory barrier - inner sharable These new barriers are not as safe as the standard rmb() and wmb(). Specifically they do not guarantee ordering between coherent and incoherent memories. The primary use case for these would be to enforce ordering of reads and writes when accessing coherent memory that is shared between the CPU and a device. It may also be noted that there is no dma_mb(). Most architectures don't provide a good mechanism for performing a coherent only full barrier without resorting to the same mechanism used in mb(). As such there isn't much to be gained in trying to define such a function. Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Michael Ellerman <michael@ellerman.id.au> Cc: Michael Neuling <mikey@neuling.org> Cc: Russell King <linux@arm.linux.org.uk> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: David Miller <davem@davemloft.net> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* Merge branch 'core-rcu-for-linus' of ↵Linus Torvalds2014-12-101-11/+29
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU updates from Ingo Molnar: "These are the main changes in this cycle: - Streamline RCU's use of per-CPU variables, shifting from "cpu" arguments to functions to "this_"-style per-CPU variable accessors. - signal-handling RCU updates. - real-time updates. - torture-test updates. - miscellaneous fixes. - documentation updates" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits) rcu: Fix FIXME in rcu_tasks_kthread() rcu: More info about potential deadlocks with rcu_read_unlock() rcu: Optimize cond_resched_rcu_qs() rcu: Add sparse check for RCU_INIT_POINTER() documentation: memory-barriers.txt: Correct example for reorderings documentation: Add atomic_long_t to atomic_ops.txt documentation: Additional restriction for control dependencies documentation: Document RCU self test boot params rcutorture: Fix rcu_torture_cbflood() memory leak rcutorture: Remove obsolete kversion param in kvm.sh rcutorture: Remove stale test configurations rcutorture: Enable RCU self test in configs rcutorture: Add early boot self tests torture: Run Linux-kernel binary out of results directory cpu: Avoid puts_pending overflow rcu: Remove "cpu" argument to rcu_cleanup_after_idle() rcu: Remove "cpu" argument to rcu_prepare_for_idle() rcu: Remove "cpu" argument to rcu_needs_cpu() rcu: Remove "cpu" argument to rcu_note_context_switch() rcu: Remove "cpu" argument to rcu_preempt_check_callbacks() ...
| * documentation: memory-barriers.txt: Correct example for reorderingsPranith Kumar2014-11-131-11/+11
| | | | | | | | | | | | | | | | | | | | | | | | Correct the example of memory orderings in memory-barriers.txt Commit 615cc2c9cf95 "Documentation/memory-barriers.txt: fix important typo re memory barriers" changed the assignment to x and y. Change the rest of the example to match this change. Reported-by: Ganesh Rapolu <ganesh.rapolu@hotmail.com> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * documentation: Additional restriction for control dependenciesPaul E. McKenney2014-11-131-0/+18
| | | | | | | | | | | | | | | | Short-circuit booleans are not defences against compilers breaking your intended control dependencies. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
* | documentation: memory-barriers: clarify relaxed io accessor semanticsWill Deacon2014-10-201-4/+9
|/ | | | | | | | | | | | | | | | | | | | | This patch extends the paragraph describing the relaxed read io accessors so that the relaxed accessors are defined to be: - Ordered with respect to each other if accessing the same peripheral - Unordered with respect to normal memory accesses - Unordered with respect to LOCK/UNLOCK operations Whilst many architectures will provide stricter semantics, ARM, Alpha and PPC can achieve significant performance gains by taking advantage of some or all of the above relaxations. Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
* memory-barriers: Fix description of 2-legged-if-based control dependenciesPaul E. McKenney2014-09-081-54/+49
| | | | | | | | | | | Sad to say, current compilers really will hoist identical stores from both branches of an "if" statement to precede the conditional. This commit therefore updates the description of control dependencies to reflect this ugly reality. Reported-by: Pranith Kumar <bobby.prani@gmail.com> Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* memory-barriers: Retain barrier() in fold-to-zero examplePaul E. McKenney2014-09-081-3/+6
| | | | | | | | The transformation in the fold-to-zero example incorrectly omits the barrier() directive. This commit therefore adds it back in. Reported-by: Pranith Kumar <pranith@gatech.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* memory-barriers: Fix control-ordering no-transitivity examplePaul E. McKenney2014-09-081-11/+17
| | | | | | | | | The control-ordering example demonstrating lack of transitivity had multiple problems. This commit fixes them. Reported-by: Nikolay Samofatov <nikolay.samofatov@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
* documentation: Add acquire/release barriers to pairing rulesPaul E. McKenney2014-07-081-4/+8
| | | | | | | | | | | It is possible to pair acquire and release barriers with other barriers, so this commit adds them to the list in the SMP barrier pairing section. Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Tejun Heo <tj@kernel.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Updated pairing discussion as suggested by Peter Zijlstra. ]
* documentation: Clarify wake-up/memory-barrier relationshipPaul E. McKenney2014-07-081-0/+15
| | | | | | | | | | | This commit adds an example demonstrating that if a wake_up() doesn't actually wake something up, no memory ordering is provided. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com> Acked-by: Peter Zijlstra <peterz@infradead.org>
* Documentation/memory-barriers.txt: fix important typo re memory barriersAlexey Dobriyan2014-06-071-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Examples introducing neccesity of RMB+WMP pair reads as A=3 READ B www rrrrrr B=4 READ A Note the opposite order of reads vs writes. But the first example without barriers reads as A=3 READ A B=4 READ B There are 4 outcomes in the first example. But if someone new to the concept tries to insert barriers like this: A=3 READ A www rrrrrr B=4 READ B he will still get all 4 possible outcomes, because "READ A" is first. All this can be utterly confusing because barrier pair seems to be superfluous. In short, fixup first example to match latter examples with barriers. Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* arch,doc: Convert smp_mb__*()Peter Zijlstra2014-04-181-31/+11
| | | | | | | | | | | | | | Update the documentation to reflect the change of barrier primitives. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Link: http://lkml.kernel.org/n/tip-xslfehiga1twbk5uk94rij1e@git.kernel.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Merge branch 'for-linus' of ↵Linus Torvalds2014-04-031-1/+1
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial Pull trivial tree updates from Jiri Kosina: "Usual rocket science -- mostly documentation and comment updates" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial: sparse: fix comment doc: fix double words isdn: capi: fix "CAPI_VERSION" comment doc: DocBook: Fix typos in xml and template file Bluetooth: add module name for btwilink driver core: unexport static function create_syslog_header mmc: core: typo fix in printk specifier ARM: spear: clean up editing mistake net-sysfs: fix comment typo 'CONFIG_SYFS' doc: Insert MODULE_ in module-signing macros Documentation: update URL to hfsplus Technote 1150 gpio: update path to documentation ixgbe: Fix format string in ixgbe_fcoe. Kconfig: Remove useless "default N" lines user_namespace.c: Remove duplicated word in comment CREDITS: fix formatting treewide: Fix typo in Documentation/DocBook mm: Fix warning on make htmldocs caused by slab.c ata: ata-samsung_cf: cleanup in header file idr: remove unused prototype of idr_free()
| * doc: fix double wordsMasanari Iida2014-03-211-1/+1
| | | | | | | | | | | | | | | | Fix double words "the the" in various files within Documentations. Signed-off-by: Masanari Iida <standby24x7@gmail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
* | Documentation/memory-barriers.txt: Clarify release/acquire orderingPaul E. McKenney2014-02-241-30/+61
| | | | | | | | | | | | | | | | | | | | | | This commit fixes a couple of typos and clarifies what happens when the CPU chooses to execute a later lock acquisition before a prior lock release, in particular, why deadlock is avoided. Reported-by: Peter Hurley <peter@hurleysoftware.com> Reported-by: James Bottomley <James.Bottomley@HansenPartnership.com> Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | Documentation/memory-barriers.txt: Need barriers() for some control dependenciesPaul E. McKenney2014-02-171-7/+19
| | | | | | | | | | | | | | | | | | | | | | | | | | Current compilers can "speculate" stores in the case where both legs of the "if" statement start with identical stores. Because the stores are identical, the compiler knows that the store will unconditionally execute regardless of the "if" condition, and so the compiler is within its rights to hoist the store to precede the condition. Such hoisting destroys the control-dependency ordering. This ordering can be restored by placing a barrier() at the beginning of each leg of the "if" statement. This commit adds this requirement to the control-dependencies section. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | Documentation/memory-barriers.txt: Conditional must use prior loadPaul E. McKenney2014-02-171-1/+2
| | | | | | | | | | | | | | | | | | A control dependency consists of a load, a conditional that depends on that load, and a store. This commit emphasizes this point in the summary. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* | Documentation/memory-barriers.txt: ACCESS_ONCE() provides cache coherencePaul E. McKenney2014-02-171-0/+17
|/ | | | | | | | | The ACCESS_ONCE() primitive provides cache coherence, but the documentation does not clearly state this. This commit therefore upgrades the documentation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* locking/doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASEPeter Zijlstra2014-01-121-116/+121
| | | | | | | | | | | | | | | | | | | | | | | | | | | The LOCK and UNLOCK barriers as described in our barrier document are generally known as ACQUIRE and RELEASE barriers in other literature. Since we plan to introduce the acquire and release nomenclature in generic kernel primitives we should amend the document to avoid confusion as to what an acquire/release means. Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Michael Ellerman <michael@ellerman.id.au> Cc: Michael Neuling <mikey@neuling.org> Cc: Russell King <linux@arm.linux.org.uk> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Victor Kaplansky <VICTORK@il.ibm.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Oleg Nesterov <oleg@redhat.com> Link: http://lkml.kernel.org/r/20131217092435.GC21999@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Downgrade UNLOCK+BLOCKPaul E. McKenney2013-12-161-15/+69
| | | | | | | | | | | | | | | | | | | | | | Historically, an UNLOCK+LOCK pair executed by one CPU, by one task, or on a given lock variable has implied a full memory barrier. In a recent LKML thread, the wisdom of this historical approach was called into question: http://www.spinics.net/lists/linux-mm/msg65653.html, in part due to the memory-order complexities of low-handoff-overhead queued locks on x86 systems. This patch therefore removes this guarantee from the documentation, and further documents how to restore it via a new smp_mb__after_unlock_lock() primitive. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-6-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Document ACCESS_ONCE()Paul E. McKenney2013-12-161-35/+271
| | | | | | | | | | | | | | | | The situations in which ACCESS_ONCE() is required are not well documented, so this commit adds some verbiage to memory-barriers.txt. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-4-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Prohibit speculative writesPeter Zijlstra2013-12-161-8/+175
| | | | | | | | | | | | | | | | | | No SMP architecture currently supporting Linux allows speculative writes, so this commit updates Documentation/memory-barriers.txt to prohibit them in Linux core code. It also records restrictions on their use. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-3-git-send-email-paulmck@linux.vnet.ibm.com [ Paul modified the original patch from Peter. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Add long atomic examples to ↵Paul E. McKenney2013-12-161-11/+13
| | | | | | | | | | | | | | | | | | memory-barriers.txt Although the atomic_long_t functions are quite useful, they are a bit obscure. This commit therefore adds the common ones alongside their atomic_t counterparts in Documentation/memory-barriers.txt. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-2-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Add needed ACCESS_ONCE() calls to ↵Paul E. McKenney2013-12-161-80/+126
| | | | | | | | | | | | | | | | | | | memory-barriers.txt The Documentation/memory-barriers.txt file was written before the need for ACCESS_ONCE() was fully appreciated. It therefore contains no ACCESS_ONCE() calls, which can be a problem when people lift examples from it. This commit therefore adds ACCESS_ONCE() calls. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-1-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* Documentation/memory-barriers.txt: Fix a typo in the data dependency descriptionIngo Molnar2013-11-221-21/+21
| | | | | | | | | | | | | | | | | This typo has been there forever, it is 7.5 years old, looks like this section of our memory ordering documentation is a place where most eyes are glazed over already ;-) [ Also fix some stray spaces and stray tabs while at it, shrinking the file by 49 bytes. Visual output unchanged. ] Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/n/tip-gncea9cb8igosblizfqMXrie@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* doc: Fix memory-barrier control-dependency examplePaul E. McKenney2013-08-201-4/+6
| | | | | | | | | | | Each control-dependency example needs its barriers between the "if" condition and the body of the "if" because a control dependency is a dependency induced by a branch. This commit makes the needed adjustment. Reported-by: Yongming Shen <symingz@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* Documentation: Memory barrier semantics of atomic_xchg()Richard Braun2013-01-081-0/+1
| | | | | | | | | Add atomic_xchg() to documentation for atomic operations and memory barriers. Signed-off-by: Richard Braun <rbraun@sceen.net> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* Documentation: Fix memory-barriers.txt examplePaul E. McKenney2012-10-231-4/+5
| | | | | | | | This commit fixes a broken example of overlapping stores in the Documentation/memory-barriers.txt file. Reported-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: fix broken referencesPaul Bolle2011-09-271-1/+1
| | | | | | | | | | | | | There are numerous broken references to Documentation files (in other Documentation files, in comments, etc.). These broken references are caused by typo's in the references, and by renames or removals of the Documentation files. Some broken references are simply odd. Fix these broken references, sometimes by dropping the irrelevant text they were part of. Signed-off-by: Paul Bolle <pebolle@tiscali.nl> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
* smp: Document transitivity for memory barriers.Paul E. McKenney2011-03-041-0/+58
| | | | | | Transitivity is guaranteed only for full memory barriers (smp_mb()). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* Document Linux's circular buffering capabilitiesDavid Howells2010-03-251-0/+20
| | | | | | | | | | Document the circular buffering capabilities available in Linux. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Randy Dunlap <rdunlap@xenotime.net> Reviewed-by: Stefan Richter <stefanr@s5r6.in-berlin.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* sched: Document memory barriers implied by sleep/wake-up primitivesDavid Howells2009-04-291-1/+128
| | | | | | | | | | | | | | | | | | Add a section to the memory barriers document to note the implied memory barriers of sleep primitives (set_current_state() and wrappers) and wake-up primitives (wake_up() and co.). Also extend the in-code comments on the wake_up() functions to note these implied barriers. [ Impact: add documentation ] Signed-off-by: David Howells <dhowells@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> LKML-Reference: <20090428140138.1192.94723.stgit@warthog.procyon.org.uk> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* read_barrier_depends arch fixletsNick Piggin2008-05-141-1/+11
| | | | | | | | | | read_barrie_depends has always been a noop (not a compiler barrier) on all architectures except SMP alpha. This brings UP alpha and frv into line with all other architectures, and fixes incorrect documentation. Signed-off-by: Nick Piggin <npiggin@suse.de> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* PCI: doc/pci: create Documentation/PCI/ and move files into itRandy Dunlap2008-04-211-2/+2
| | | | | | | | | | | Create Documentation/PCI/ and move PCI-related files to it. Fix a few instances of trailing whitespace. Update references to the new file locations. Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
* documentation: atomic_add_unless() doesn't imply mb() on failureOleg Nesterov2008-02-241-1/+1
| | | | | | | | | | | | | | (sorry for being offtpoic, but while experts are here...) A "typical" implementation of atomic_add_unless() can return 0 immediately after the first atomic_read() (before doing cmpxchg). In that case it doesn't provide any barrier semantics. See include/asm-ia64/atomic.h as an example. We should either change the implementation, or fix the docs. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* bitops: introduce lock opsNick Piggin2007-10-181-2/+12
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Introduce test_and_set_bit_lock / clear_bit_unlock bitops with lock semantics. Convert all architectures to use the generic implementation. Signed-off-by: Nick Piggin <npiggin@suse.de> Acked-By: David Howells <dhowells@redhat.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Haavard Skinnemoen <hskinnemoen@atmel.com> Cc: Bryan Wu <bryan.wu@analog.com> Cc: Mikael Starvik <starvik@axis.com> Cc: David Howells <dhowells@redhat.com> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Hirokazu Takata <takata@linux-m32r.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Greg Ungerer <gerg@uclinux.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Kyle McMartin <kyle@mcmartin.ca> Cc: Matthew Wilcox <willy@debian.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Kazumoto Kojima <kkojima@rr.iij4u.or.jp> Cc: Richard Curnow <rc@rc0.org.uk> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Jeff Dike <jdike@addtoit.com> Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Cc: Miles Bader <uclinux-v850@lsi.nec.co.jp> Cc: Andi Kleen <ak@muc.de> Cc: Chris Zankel <chris@zankel.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Documentation/memory-barriers.txt: various fixesJarek Poplawski2007-05-241-49/+49
| | | | | | | | | | Fix various grammatical issues in Documentation/memory-barriers.txt. Cc: "Robert P. J. Day" <rpjday@mindspring.com> Signed-off-by: Jarek Poplawski <jarkao2@o2.pl> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Fix typos in /Documentation : 'T''Matt LaPlante2006-11-301-1/+1
| | | | | | | | | This patch fixes typos in various Documentation txts. The patch addresses some +words starting with the letter 'T'. Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Adrian Bunk <bunk@stusta.de>
* [PATCH] A minor fix for set_mb() in Documentation/memory-barriers.txtOleg Nesterov2006-11-091-1/+1
| | | | | | | | | | | set_mb() is used by set_current_state() which needs mb(), not wmb(). I think it would be right to assume that set_mb() implies mb(), all arches seem to do just this. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] fix typo in memory barrier docsPaolo 'Blaisorblade' Giarrusso2006-10-201-1/+1
| | | | | | | | | | Fix cut'n'paste typo - &a and &b are used in other examples, in this one the doc uses &u and &v. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* Documentation: remove duplicated wordsPaolo Ornati2006-10-031-1/+1
| | | | | | | | | | | | | | | Remove many duplicated words under Documentation/ and do other small cleanups. Examples: "and and" --> "and" "in in" --> "in" "the the" --> "the" "the the" --> "to the" ... Signed-off-by: Paolo Ornati <ornati@fastwebnet.it> Signed-off-by: Adrian Bunk <bunk@stusta.de>
* Fix some typos in Documentation/: 'A'Matt LaPlante2006-10-031-1/+1
| | | | | | | | | | This patch fixes typos in various Documentation txts. This patch addresses some words starting with the letter 'A'. Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Acked-by: Alan Cox <alan@redhat.com> Signed-off-by: Adrian Bunk <bunk@stusta.de>
* [PATCH] remove set_wmb - doc updateSteven Rostedt2006-07-151-3/+2
| | | | | | | | This patch removes the reference to set_wmb from memory-barriers.txt since it shouldn't be used. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* typo fixes: occuring -> occurringAdrian Bunk2006-06-301-1/+1
| | | | Signed-off-by: Adrian Bunk <bunk@stusta.de>
* [PATCH] Corrections to memory barrier docDavid Howells2006-06-251-10/+9
| | | | | | | | | | | | Apply some small corrections to the memory barrier document, as contributed by: Christoph Lameter <clameter@sgi.com> Kirill Smelkov <kirr@mns.spb.ru> Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Another couple of alterations to the memory barrier docDavid Howells2006-06-251-5/+10
| | | | | | | | | | | | | | | | Make another couple of alterations to the memory barrier document following suggestions by Alan Stern and in co-operation with Paul McKenney: (*) Rework the point of introduction of memory barriers and the description of what they are to reiterate why they're needed. (*) Modify a statement about the use of data dependency barriers to note that other barriers can be used instead (as they imply DD-barriers). Signed-off-by: David Howells <dhowells@redhat.com> Acked-By: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Further alterations for memory barrier documentDavid Howells2006-06-101-78/+270
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | From: David Howells <dhowells@redhat.com> Apply some alterations to the memory barrier document that I worked out with Paul McKenney of IBM, plus some of the alterations suggested by Alan Stern. The following changes were made: (*) One of the examples given for what can happen with overlapping memory barriers was wrong. (*) The description of general memory barriers said that a general barrier is a combination of a read barrier and a write barrier. This isn't entirely true: it implies both, but is more than a combination of both. (*) The first example in the "SMP Barrier Pairing" section was wrong: the loads around the read barrier need to touch the memory locations in the opposite order to the stores around the write barrier. (*) Added a note to make explicit that the loads should be in reverse order to the stores. (*) Adjusted the diagrams in the "Examples Of Memory Barrier Sequences" section to make them clearer. Added a couple of diagrams to make it more clear as to how it could go wrong without the barrier. (*) Added a section on memory speculation. (*) Dropped any references to memory allocation routines doing memory barriers. They may do sometimes, but it can't be relied on. This may be worthy of further documentation later. (*) Made the fact that a LOCK followed by an UNLOCK should not be considered a full memory barrier more explicit and gave an example. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Fix typos in Documentation/memory-barriers.txtAneesh Kumar2006-05-151-2/+2
| | | | | | | | | Fix some typos in Documentation/memory-barriers.txt Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@gmail.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Improve data-dependency memory barrier example in documentationDavid Howells2006-04-111-1/+15
| | | | | | | | | | | | | | | In the memory barrier document, improve the example of the data dependency barrier situation by: (1) showing the initial values of the variables involved; and (2) repeating the instruction sequence description, this time with the data dependency barrier actually shown to make it clear what the revised sequence actually is. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Fix memory barrier docs wrt atomic opsDavid Howells2006-04-111-19/+33
| | | | | | | | | | | | | | | | | | | | | Fix the memory barrier documentation to attempt to describe atomic ops correctly. atomic_t ops that return a value _do_ imply smp_mb() either side, and so don't actually require smp_mb__*_atomic_*() special barriers. Also explains why special barriers exist in addition to normal barriers. Further fix the memory barrier documents to portray bitwise operation memory barrier effects correctly following Nick Piggin's comments. It makes the point that any atomic op that both modifies some state in memory and returns information on that state implies memory barriers on both sides. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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