user/sven/linux.git/include/linux/seqlock.h, branch v3.16.3

seqlock: Use raw_ prefix instead of _no_lockdep

2014-01-12T09:13:59Z

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 Reviewed-by: Stephen Boyd Signed-off-by: John Stultz Signed-off-by: Peter Zijlstra Cc: Krzysztof Hałasa Cc: Uwe Kleine-König Cc: Willy Tarreau Link: http://lkml.kernel.org/r/1388704274-5278-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar

take read_seqbegin_or_lock() and friends to seqlock.h

2013-11-16T03:04:17Z

Signed-off-by: Al Viro

seqcount: Add lockdep functionality to seqcount/seqlock structures

2013-11-06T11:40:26Z

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 Signed-off-by: Peter Zijlstra Cc: Eric Dumazet Cc: Li Zefan Cc: Mathieu Desnoyers Cc: Steven Rostedt Cc: "David S. Miller" 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

seqlock: Add a new locking reader type

2013-09-12T16:25:23Z

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 Cc: Alexander Viro Signed-off-by: Linus Torvalds

seqlock: Use seqcount infrastructure

2013-02-19T07:43:34Z

No point in having different implementations for the same thing. Change the macro mess to inline functions where possible. Signed-off-by: Thomas Gleixner

seqlock: Remove unused functions

2013-02-19T07:43:33Z

Signed-off-by: Thomas Gleixner

seqlock: add 'raw_seqcount_begin()' function

2012-05-04T22:13:54Z

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

Fix __read_seqcount_begin() to use ACCESS_ONCE for sequence value read

2012-05-04T21:46:02Z

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

linux/seqlock.h should #include asm/processor.h for cpu_relax()

2011-06-11T20:17:28Z

It uses cpu_relax(), and so needs 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 Signed-off-by: Linus Torvalds

seqlock: Get rid of SEQLOCK_UNLOCKED

2011-05-24T13:22:17Z

All static seqlock should be initialized with the lockdep friendly __SEQLOCK_UNLOCKED() macro. Remove legacy SEQLOCK_UNLOCKED() macro. Signed-off-by: Eric Dumazet Cc: David Miller Link: http://lkml.kernel.org/r/%3C1306238888.3026.31.camel%40edumazet-laptop%3E Signed-off-by: Thomas Gleixner