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2011-09-13locking, rwsem: Annotate inner lock as rawThomas Gleixner1-7/+7
There is no reason to allow the lock protecting rwsems (the ownerless variant) to be preemptible on -rt. Convert it to raw. In mainline this change documents the low level nature of the lock - otherwise there's no functional difference. Lockdep and Sparse checking will work as usual. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-27rwsem: Remove redundant asmregparm annotationThomas Gleixner1-6/+4
Peter Zijlstra pointed out, that the only user of asmregparm (x86) is compiling the kernel already with -mregparm=3. So the annotation of the rwsem functions is redundant. Remove it. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: David Howells <dhowells@redhat.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Matt Turner <mattst88@gmail.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: David Miller <davem@davemloft.net> Cc: Chris Zankel <chris@zankel.net> LKML-Reference: <alpine.LFD.2.00.1101262130450.31804@localhost6.localdomain6> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2010-08-09rwsem: smaller wrappers around rwsem_down_failed_commonMichel Lespinasse1-15/+10
More code can be pushed from rwsem_down_read_failed and rwsem_down_write_failed into rwsem_down_failed_common. Following change adding down_read_critical infrastructure support also enjoys having flags available in a register rather than having to fish it out in the struct rwsem_waiter... Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Mike Waychison <mikew@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Ying Han <yinghan@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.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>
2010-08-09rwsem: wake queued readers when writer blocks on active read lockMichel Lespinasse1-4/+15
This change addresses the following situation: - Thread A acquires the rwsem for read - Thread B tries to acquire the rwsem for write, notices there is already an active owner for the rwsem. - Thread C tries to acquire the rwsem for read, notices that thread B already tried to acquire it. - Thread C grabs the spinlock and queues itself on the wait queue. - Thread B grabs the spinlock and queues itself behind C. At this point A is the only remaining active owner on the rwsem. In this situation thread B could notice that it was the last active writer on the rwsem, and decide to wake C to let it proceed in parallel with A since they both only want the rwsem for read. Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Mike Waychison <mikew@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Ying Han <yinghan@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.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>
2010-08-09rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threadsMichel Lespinasse1-11/+17
Previously each waiting thread added a bias of RWSEM_WAITING_BIAS. With this change, the bias is added only once to indicate that the wait list is non-empty. This has a few nice properties which will be used in following changes: - when the spinlock is held and the waiter list is known to be non-empty, count < RWSEM_WAITING_BIAS <=> there is an active writer on that sem - count == RWSEM_WAITING_BIAS <=> there are waiting threads and no active readers/writers on that sem Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Mike Waychison <mikew@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Ying Han <yinghan@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.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>
2010-08-09rwsem: lighter active count checks when waking up readersMichel Lespinasse1-25/+32
In __rwsem_do_wake(), we can skip the active count check unless we come there from up_xxxx(). Also when checking the active count, it is not actually necessary to increment it; this allows us to get rid of the read side undo code and simplify the calculation of the final rwsem count adjustment once we've counted the reader threads to wake. The basic observation is the following. When there are waiter threads on a rwsem and the spinlock is held, other threads can only increment the active count by trying to grab the rwsem in down_xxxx(). However down_xxxx() will notice there are waiter threads and take the down_failed path, blocking to acquire the spinlock on the way there. Therefore, a thread observing an active count of zero with waiters queued and the spinlock held, is protected against other threads acquiring the rwsem until it wakes the last waiter or releases the spinlock. Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Mike Waychison <mikew@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Ying Han <yinghan@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.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>
2010-08-09rwsem: fully separate code paths to wake writers vs readersMichel Lespinasse1-27/+34
This is in preparation for later changes in the series. In __rwsem_do_wake(), the first queued waiter is checked first in order to determine whether it's a writer or a reader. The code paths diverge at this point. The code that checks and increments the rwsem active count is duplicated on both sides - the point is that later changes in the series will be able to independently modify both sides. Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Mike Waychison <mikew@google.com> Cc: Suleiman Souhlal <suleiman@google.com> Cc: Ying Han <yinghan@google.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.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>
2010-05-12rwsem: Test for no active locks in __rwsem_do_wake undo codeMichel Lespinasse1-2/+3
If there are no active threasd using a semaphore, it is always correct to unqueue blocked threads. This seems to be what was intended in the undo code. What was done instead, was to look for a sem count of zero - this is an impossible situation, given that at least one thread is known to be queued on the semaphore. The code might be correct as written, but it's hard to reason about and it's not what was intended (otherwise the goto out would have been unconditional). Go for checking the active count - the alternative is not worth the headache. Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-01-30x86: fix UML and -regparm=3Ingo Molnar1-4/+4
introduce the "asmregparm" calling convention: for functions implemented in assembly with a fixed regparm input parameters calling convention. mark the semaphore and rwsem slowpath functions with that. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2007-12-18sched: mark rwsem functions as __sched for wchan/profilingLivio Soares1-1/+1
This following commit http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=fdf8cb0909b531f9ae8f9b9d7e4eb35ba3505f07 un-inlined a low-level rwsem function, but did not mark it as __sched. The result is that it now shows up as thread wchan (which also affects /proc/profile stats). The following simple patch fixes this by properly marking rwsem_down_failed_common() as a __sched function. Also in this patch, which is up for discussion, marks down_read() and down_write() proper as __sched. For profiling, it is pretty much useless to know that a semaphore is beig help - it is necessary to know _which_ one. By going up another frame on the stack, the information becomes much more useful. In summary, the below change to lib/rwsem.c should be applied; the changes to kernel/rwsem.c could be applied if other kernel hackers agree with my proposal that down_read()/down_write() in the profile is not enough. [ akpm@linux-foundation.org: build fix ] Signed-off-by: Livio Soares <livio@eecg.toronto.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2006-10-11Lockdep: add lockdep_set_class_and_subclass() and lockdep_set_subclass()Peter Zijlstra1-1/+1
This annotation makes it possible to assign a subclass on lock init. This annotation is meant to reduce the _nested() annotations by assigning a default subclass. One could do without this annotation and rely on lockdep_set_class() exclusively, but that would require a manual stack of struct lock_class_key objects. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
2006-09-29[PATCH] lib/rwsem.c: un-inline rwsem_down_failed_common()Andreas Mohr1-1/+1
Un-inlining rwsem_down_failed_common() (two callsites) reduced lib/rwsem.o on my Athlon, gcc 4.1.2 from 5935 to 5480 Bytes (455 Bytes saved). I thus guess that reduced icache footprint (and better function caching) is worth more than any function call overhead. Signed-off-by: Andreas Mohr <andi@lisas.de> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-03[PATCH] lockdep: prove rwsem locking correctnessIngo Molnar1-0/+20
Use the lock validator framework to prove rwsem locking correctness. 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>
2006-07-03[PATCH] lockdep: clean up rwsemsIngo Molnar1-31/+0
Clean up rwsems. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-05-01[PATCH] use smp_mb/wmb/rmb where possibleakpm@osdl.org1-2/+2
Replace a number of memory barriers with smp_ variants. This means we won't take the unnecessary hit on UP machines. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-04-16Linux-2.6.12-rc2v2.6.12-rc2Linus Torvalds1-0/+268
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!
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