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2016-06-03locking/seqcount: Re-fix raw_read_seqcount_latch()Peter Zijlstra1-2/+5
Commit 50755bc1c305 ("seqlock: fix raw_read_seqcount_latch()") broke raw_read_seqcount_latch(). If you look at the comment that was modified; the thing that changes is the seq count, not the latch pointer. * void latch_modify(struct latch_struct *latch, ...) * { * smp_wmb(); <- Ensure that the last data[1] update is visible * latch->seq++; * smp_wmb(); <- Ensure that the seqcount update is visible * * modify(latch->data[0], ...); * * smp_wmb(); <- Ensure that the data[0] update is visible * latch->seq++; * smp_wmb(); <- Ensure that the seqcount update is visible * * modify(latch->data[1], ...); * } * * The query will have a form like: * * struct entry *latch_query(struct latch_struct *latch, ...) * { * struct entry *entry; * unsigned seq, idx; * * do { * seq = lockless_dereference(latch->seq); So here we have: seq = READ_ONCE(latch->seq); smp_read_barrier_depends(); Which is exactly what we want; the new code: seq = ({ p = READ_ONCE(latch); smp_read_barrier_depends(); p })->seq; is just wrong; because it looses the volatile read on seq, which can now be torn or worse 'optimized'. And the read_depend barrier is also placed wrong, we want it after the load of seq, to match the above data[] up-to-date wmb()s. Such that when we dereference latch->data[] below, we're guaranteed to observe the right data. * * idx = seq & 0x01; * entry = data_query(latch->data[idx], ...); * * smp_rmb(); * } while (seq != latch->seq); * * return entry; * } So yes, not passing a pointer is not pretty, but the code was correct, and isn't anymore now. Change to explicit READ_ONCE()+smp_read_barrier_depends() to avoid confusion and allow strict lockless_dereference() checking. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: 50755bc1c305 ("seqlock: fix raw_read_seqcount_latch()") Link: http://lkml.kernel.org/r/20160527111117.GL3192@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-05-26seqlock: fix raw_read_seqcount_latch()Alexey Dobriyan1-2/+2
lockless_dereference() is supposed to take pointer not integer. Link: http://lkml.kernel.org/r/20160521201448.GA7429@p183.telecom.by Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-07-01Merge tag 'modules-next-for-linus' of ↵Linus Torvalds1-1/+80
git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux Pull module updates from Rusty Russell: "Main excitement here is Peter Zijlstra's lockless rbtree optimization to speed module address lookup. He found some abusers of the module lock doing that too. A little bit of parameter work here too; including Dan Streetman's breaking up the big param mutex so writing a parameter can load another module (yeah, really). Unfortunately that broke the usual suspects, !CONFIG_MODULES and !CONFIG_SYSFS, so those fixes were appended too" * tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux: (26 commits) modules: only use mod->param_lock if CONFIG_MODULES param: fix module param locks when !CONFIG_SYSFS. rcu: merge fix for Convert ACCESS_ONCE() to READ_ONCE() and WRITE_ONCE() module: add per-module param_lock module: make perm const params: suppress unused variable error, warn once just in case code changes. modules: clarify CONFIG_MODULE_COMPRESS help, suggest 'N'. kernel/module.c: avoid ifdefs for sig_enforce declaration kernel/workqueue.c: remove ifdefs over wq_power_efficient kernel/params.c: export param_ops_bool_enable_only kernel/params.c: generalize bool_enable_only kernel/module.c: use generic module param operaters for sig_enforce kernel/params: constify struct kernel_param_ops uses sysfs: tightened sysfs permission checks module: Rework module_addr_{min,max} module: Use __module_address() for module_address_lookup() module: Make the mod_tree stuff conditional on PERF_EVENTS || TRACING module: Optimize __module_address() using a latched RB-tree rbtree: Implement generic latch_tree seqlock: Introduce raw_read_seqcount_latch() ...
2015-06-19seqcount: Introduce raw_write_seqcount_barrier()Peter Zijlstra1-0/+41
Introduce raw_write_seqcount_barrier(), a new construct that can be used to provide write barrier semantics in seqcount read loops instead of the usual consistency guarantee. raw_write_seqcount_barier() is equivalent to: raw_write_seqcount_begin(); raw_write_seqcount_end(); But avoids issueing two back-to-back smp_wmb() instructions. This construct works because the read side will 'stall' when observing odd values. This means that -- referring to the example in the comment below -- even though there is no (matching) read barrier between the loads of X and Y, we cannot observe !x && !y, because: - if we observe Y == false we must observe the first sequence increment, which makes us loop, until - we observe !(seq & 1) -- the second sequence increment -- at which time we must also observe T == true. Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: umgwanakikbuti@gmail.com Cc: ktkhai@parallels.com Cc: rostedt@goodmis.org Cc: juri.lelli@gmail.com Cc: pang.xunlei@linaro.org Cc: oleg@redhat.com Cc: wanpeng.li@linux.intel.com Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20150617122924.GP3644@twins.programming.kicks-ass.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-06-19seqcount: Rename write_seqcount_barrier()Peter Zijlstra1-3/+3
I'll shortly be introducing another seqcount primitive that's useful to provide ordering semantics and would like to use the write_seqcount_barrier() name for that. Seeing how there's only one user of the current primitive, lets rename it to invalidate, as that appears what its doing. While there, employ lockdep_assert_held() instead of assert_spin_locked() to not generate debug code for regular kernels. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: ktkhai@parallels.com Cc: rostedt@goodmis.org Cc: juri.lelli@gmail.com Cc: pang.xunlei@linaro.org Cc: Oleg Nesterov <oleg@redhat.com> Cc: wanpeng.li@linux.intel.com Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: umgwanakikbuti@gmail.com Link: http://lkml.kernel.org/r/20150611124743.279926217@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-05-28seqlock: Introduce raw_read_seqcount_latch()Peter Zijlstra1-2/+7
Because with latches there is a strict data dependency on the seq load we can avoid the rmb in favour of a read_barrier_depends. Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-28seqlock: Better document raw_write_seqcount_latch()Peter Zijlstra1-1/+75
Improve the documentation of the latch technique as used in the current timekeeping code, such that it can be readily employed elsewhere. Borrow from the comments in timekeeping and replace those with a reference to this more generic comment. Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <David.Woodhouse@intel.com> Cc: Rik van Riel <riel@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Michel Lespinasse <walken@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-02-24locking: Remove ACCESS_ONCE() usageDavidlohr Bueso1-3/+3
With the new standardized functions, we can replace all ACCESS_ONCE() calls across relevant locking - this includes lockref and seqlock while at it. ACCESS_ONCE() does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 Update the new calls regardless of if it is a scalar type, this is cleaner than having three alternatives. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> 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/r/1424662301.6539.18.camel@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-09-19seqlock: Add irqsave variant of read_seqbegin_or_lock()Rik van Riel1-0/+19
There are cases where read_seqbegin_or_lock() needs to block irqs, because the seqlock in question nests inside a lock that is also be taken from irq context. Add read_seqbegin_or_lock_irqsave() and done_seqretry_irqrestore(), which are almost identical to read_seqbegin_or_lock() and done_seqretry(). Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: prarit@redhat.com Cc: oleg@redhat.com Cc: sgruszka@redhat.com Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: John Stultz <john.stultz@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Stephen Boyd <sboyd@codeaurora.org> Cc: Trond Myklebust <trond.myklebust@primarydata.com> Link: http://lkml.kernel.org/r/1410527535-9814-2-git-send-email-riel@redhat.com [ Improved the readability of the code a bit. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-08-05Merge branch 'timers-core-for-linus' of ↵Linus Torvalds1-0/+27
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull timer and time updates from Thomas Gleixner: "A rather large update of timers, timekeeping & co - Core timekeeping code is year-2038 safe now for 32bit machines. Now we just need to fix all in kernel users and the gazillion of user space interfaces which rely on timespec/timeval :) - Better cache layout for the timekeeping internal data structures. - Proper nanosecond based interfaces for in kernel users. - Tree wide cleanup of code which wants nanoseconds but does hoops and loops to convert back and forth from timespecs. Some of it definitely belongs into the ugly code museum. - Consolidation of the timekeeping interface zoo. - A fast NMI safe accessor to clock monotonic for tracing. This is a long standing request to support correlated user/kernel space traces. With proper NTP frequency correction it's also suitable for correlation of traces accross separate machines. - Checkpoint/restart support for timerfd. - A few NOHZ[_FULL] improvements in the [hr]timer code. - Code move from kernel to kernel/time of all time* related code. - New clocksource/event drivers from the ARM universe. I'm really impressed that despite an architected timer in the newer chips SoC manufacturers insist on inventing new and differently broken SoC specific timers. [ Ed. "Impressed"? I don't think that word means what you think it means ] - Another round of code move from arch to drivers. Looks like most of the legacy mess in ARM regarding timers is sorted out except for a few obnoxious strongholds. - The usual updates and fixlets all over the place" * 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (114 commits) timekeeping: Fixup typo in update_vsyscall_old definition clocksource: document some basic timekeeping concepts timekeeping: Use cached ntp_tick_length when accumulating error timekeeping: Rework frequency adjustments to work better w/ nohz timekeeping: Minor fixup for timespec64->timespec assignment ftrace: Provide trace clocks monotonic timekeeping: Provide fast and NMI safe access to CLOCK_MONOTONIC seqcount: Add raw_write_seqcount_latch() seqcount: Provide raw_read_seqcount() timekeeping: Use tk_read_base as argument for timekeeping_get_ns() timekeeping: Create struct tk_read_base and use it in struct timekeeper timekeeping: Restructure the timekeeper some more clocksource: Get rid of cycle_last clocksource: Move cycle_last validation to core code clocksource: Make delta calculation a function wireless: ath9k: Get rid of timespec conversions drm: vmwgfx: Use nsec based interfaces drm: i915: Use nsec based interfaces timekeeping: Provide ktime_get_raw() hangcheck-timer: Use ktime_get_ns() ...
2014-07-23seqcount: Add raw_write_seqcount_latch()Mathieu Desnoyers1-0/+11
For NMI safe access to clock monotonic we use the seqcount LSB as index of a timekeeper array. The update sequence looks like this: smp_wmb(); <- prior stores to a[1] seq++; smp_wmb(); <- seq increment before update of a[0] update(a[0]); smp_wmb(); <- update of a[0] seq++; smp_wmb(); <- seq increment before update of a[1] update(a[1]); To avoid open coded barriers, provide a helper function. [ tglx: Split out of a combo patch against the first implementation of the NMI safe accessor ] Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
2014-07-23seqcount: Provide raw_read_seqcount()Thomas Gleixner1-0/+16
raw_read_seqcount opens a read critical section of the given seqcount without any lockdep checking and without checking or masking the LSB. Calling code is responsible for handling that. Preparatory patch to provide a NMI safe clock monotonic accessor function. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: John Stultz <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: John Stultz <john.stultz@linaro.org>
2014-06-18lockdep: Revert lockdep check in raw_seqcount_begin()Trond Myklebust1-2/+0
This commit reverts the addition of lockdep checking to raw_seqcount_begin for the following reasons: 1) It violates the naming convention that raw_* functions should not do lockdep checks (a convention that is also followed by the other raw_*_seqcount_begin functions). 2) raw_seqcount_begin does not spin, so it can only be part of an ABBA deadlock in very special circumstances (for instance if a lock is held across the entire raw_seqcount_begin()+read_seqcount_retry() loop while also being taken inside the write_seqcount protected area). 3) It is causing false positives with some existing callers, and there is no non-lockdep alternative for those callers to use. None of the three existing callers (__d_lookup_rcu, netdev_get_name, and the NFS state code) appear to use the function in a manner that is ABBA deadlock prone. Fixes: 1ca7d67cf5d5: seqcount: Add lockdep functionality to seqcount/seqlock Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: John Stultz <john.stultz@linaro.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Waiman Long <Waiman.Long@hp.com> Cc: Stephen Boyd <sboyd@codeaurora.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CAHQdGtRR6SvEhXiqWo24hoUh9AU9cL82Z8Z-d8-7u951F_d+5g@mail.gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-01-12seqlock: Use raw_ prefix instead of _no_lockdepJohn Stultz1-8/+19
Linus disliked the _no_lockdep() naming, so instead use the more-consistent raw_* prefix to the non-lockdep enabled seqcount methods. This also adds raw_ methods for the write operations as well, which will be utilized in a following patch. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Stephen Boyd <sboyd@codeaurora.org> Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Krzysztof Hałasa <khalasa@piap.pl> Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Cc: Willy Tarreau <w@1wt.eu> Link: http://lkml.kernel.org/r/1388704274-5278-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-11-15take read_seqbegin_or_lock() and friends to seqlock.hAl Viro1-0/+29
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-11-06seqcount: Add lockdep functionality to seqcount/seqlock structuresJohn Stultz1-7/+72
Currently seqlocks and seqcounts don't support lockdep. After running across a seqcount related deadlock in the timekeeping code, I used a less-refined and more focused variant of this patch to narrow down the cause of the issue. This is a first-pass attempt to properly enable lockdep functionality on seqlocks and seqcounts. Since seqcounts are used in the vdso gettimeofday code, I've provided non-lockdep accessors for those needs. I've also handled one case where there were nested seqlock writers and there may be more edge cases. Comments and feedback would be appreciated! Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Li Zefan <lizefan@huawei.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: netdev@vger.kernel.org Link: http://lkml.kernel.org/r/1381186321-4906-3-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-09-12seqlock: Add a new locking reader typeWaiman Long1-5/+63
The sequence lock (seqlock) was originally designed for the cases where the readers do not need to block the writers by making the readers retry the read operation when the data change. Since then, the use cases have been expanded to include situations where a thread does not need to change the data (effectively a reader) at all but have to take the writer lock because it can't tolerate changes to the protected structure. Some examples are the d_path() function and the getcwd() syscall in fs/dcache.c where the functions take the writer lock on rename_lock even though they don't need to change anything in the protected data structure at all. This is inefficient as a reader is now blocking other sequence number reading readers from moving forward by pretending to be a writer. This patch tries to eliminate this inefficiency by introducing a new type of locking reader to the seqlock locking mechanism. This new locking reader will try to take an exclusive lock preventing other writers and locking readers from going forward. However, it won't affect the progress of the other sequence number reading readers as the sequence number won't be changed. Signed-off-by: Waiman Long <Waiman.Long@hp.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-02-19seqlock: Use seqcount infrastructureThomas Gleixner1-82/+92
No point in having different implementations for the same thing. Change the macro mess to inline functions where possible. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2013-02-19seqlock: Remove unused functionsThomas Gleixner1-21/+0
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2012-05-04seqlock: add 'raw_seqcount_begin()' functionLinus Torvalds1-0/+21
The normal read_seqcount_begin() function will wait for any current writers to exit their critical region by looping until the sequence count is even. That "wait for sequence count to stabilize" is the right thing to do if the read-locker will just retry the whole operation on contention: no point in doing a potentially expensive reader sequence if we know at the beginning that we'll just end up re-doing it all. HOWEVER. Some users don't actually retry the operation, but instead will abort and do the operation with proper locking. So the sequence count case may be the optimistic quick case, but in the presense of writers you may want to do full locking in order to guarantee forward progress. The prime example of this would be the RCU name lookup. And in that case, you may well be better off without the "retry early", and are in a rush to instead get to the failure handling. Thus this "raw" interface that just returns the sequence number without testing it - it just forces the low bit to zero so that read_seqcount_retry() will always fail such a "active concurrent writer" scenario. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-05-04Fix __read_seqcount_begin() to use ACCESS_ONCE for sequence value readLinus Torvalds1-1/+1
We really need to use a ACCESS_ONCE() on the sequence value read in __read_seqcount_begin(), because otherwise the compiler might end up reloading the value in between the test and the return of it. As a result, it might end up returning an odd value (which means that a write is in progress). If the reader is then fast enough that that odd value is still the current one when the read_seqcount_retry() is done, we might end up with a "successful" read sequence, even despite the concurrent write being active. In practice this probably never really happens - there just isn't anything else going on around the read of the sequence count, and the common case is that we end up having a read barrier immediately afterwards. So the code sequence in which gcc might decide to reaload from memory is small, and there's no reason to believe it would ever actually do the reload. But if the compiler ever were to decide to do so, it would be incredibly annoying to debug. Let's just make sure. Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-06-11linux/seqlock.h should #include asm/processor.h for cpu_relax()David Howells1-0/+1
It uses cpu_relax(), and so needs <asm/processor.h> Without this patch, I see: CC arch/mn10300/kernel/asm-offsets.s In file included from include/linux/time.h:8, from include/linux/timex.h:56, from include/linux/sched.h:57, from arch/mn10300/kernel/asm-offsets.c:7: include/linux/seqlock.h: In function 'read_seqbegin': include/linux/seqlock.h:91: error: implicit declaration of function 'cpu_relax' whilst building asb2364_defconfig on MN10300. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-05-24seqlock: Get rid of SEQLOCK_UNLOCKEDEric Dumazet1-3/+0
All static seqlock should be initialized with the lockdep friendly __SEQLOCK_UNLOCKED() macro. Remove legacy SEQLOCK_UNLOCKED() macro. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Link: http://lkml.kernel.org/r/%3C1306238888.3026.31.camel%40edumazet-laptop%3E Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2011-05-12seqlock: Don't smp_rmb in seqlock reader spin loopMilton Miller1-2/+2
Move the smp_rmb after cpu_relax loop in read_seqlock and add ACCESS_ONCE to make sure the test and return are consistent. A multi-threaded core in the lab didn't like the update from 2.6.35 to 2.6.36, to the point it would hang during boot when multiple threads were active. Bisection showed af5ab277ded04bd9bc6b048c5a2f0e7d70ef0867 (clockevents: Remove the per cpu tick skew) as the culprit and it is supported with stack traces showing xtime_lock waits including tick_do_update_jiffies64 and/or update_vsyscall. Experimentation showed the combination of cpu_relax and smp_rmb was significantly slowing the progress of other threads sharing the core, and this patch is effective in avoiding the hang. A theory is the rmb is affecting the whole core while the cpu_relax is causing a resource rebalance flush, together they cause an interfernce cadance that is unbroken when the seqlock reader has interrupts disabled. At first I was confused why the refactor in 3c22cd5709e8143444a6d08682a87f4c57902df3 (kernel: optimise seqlock) didn't affect this patch application, but after some study that affected seqcount not seqlock. The new seqcount was not factored back into the seqlock. I defer that the future. While the removal of the timer interrupt offset created contention for the xtime lock while a cpu does the additonal work to update the system clock, the seqlock implementation with the tight rmb spin loop goes back much further, and is just waiting for the right trigger. Cc: <stable@vger.kernel.org> Signed-off-by: Milton Miller <miltonm@bga.com> Cc: <linuxppc-dev@lists.ozlabs.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andi Kleen <andi@firstfloor.org> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Anton Blanchard <anton@samba.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Eric Dumazet <eric.dumazet@gmail.com> Link: http://lkml.kernel.org/r/%3Cseqlock-rmb%40mdm.bga.com%3E Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2011-01-07kernel: optimise seqlockNick Piggin1-7/+73
Add branch annotations for seqlock read fastpath, and introduce __read_seqcount_begin and __read_seqcount_end functions, that can avoid the smp_rmb() if used carefully. These will be used by store-free path walking algorithm performance is critical and seqlocks are in use. Signed-off-by: Nick Piggin <npiggin@kernel.dk>
2008-04-25seqlock: livelock fixIngo Molnar1-17/+29
Thomas Gleixner debugged a particularly ugly seqlock related livelock: do not process the seq-read section if we know it beforehand that the test at the end of the section will fail ... Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-04-27seqlocks: trivial remove weird whitespaceDaniel Walker1-4/+4
Signed-off-by: Daniel Walker <dwalker@mvista.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-17Various typo fixes.Robert P. J. Day1-1/+1
Correct mis-spellings of "algorithm", "appear", "consistent" and (shame, shame) "kernel". Signed-off-by: Robert P. J. Day <rpjday@mindspring.com> Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-12-12[PATCH] lockdep: fix seqlock_init()Ingo Molnar1-2/+5
seqlock_init() needs to use spin_lock_init() for dynamic locks, so that lockdep is notified about the presence of a new lock. (this is a fallout of the recent networking merge, which started using the so-far unused seqlock_init() API.) This fix solves the following lockdep-internal warning on current -git: INFO: trying to register non-static key. the code is fine but needs lockdep annotation. turning off the locking correctness validator. __lock_acquire+0x10c/0x9f9 lock_acquire+0x56/0x72 _spin_lock+0x35/0x42 neigh_destroy+0x9d/0x12e neigh_periodic_timer+0x10a/0x15c run_timer_softirq+0x126/0x18e __do_softirq+0x6b/0xe6 do_softirq+0x64/0xd2 ksoftirqd+0x82/0x138 Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-03[PATCH] lockdep: locking init debugging improvementIngo Molnar1-2/+10
Locking init improvement: - introduce and use __SPIN_LOCK_UNLOCKED for array initializations, to pass in the name string of locks, used by debugging 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>
2006-04-26Don't include linux/config.h from anywhere else in include/David Woodhouse1-1/+0
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
2006-04-11[PATCH] x86_64: inline function prefix with __always_inline in vsyscallmao, bibo1-2/+2
In vsyscall function do_vgettimeofday(), some functions are declared as inlined, which is a hint for gcc to compile the function inlined but it not forced. Sometimes compiler does not compile the function as inlined, so here inline is replaced by __always_inline prefix. It does not happen in gcc compiler actually, but it possibly happens. Signed-off-by: bibo mao <bibo.mao@intel.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-04-16Linux-2.6.12-rc2Linus Torvalds1-0/+175
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!