1. 20 Aug, 2010 1 commit
  2. 19 Aug, 2010 1 commit
    • Paul E. McKenney's avatar
      rcu: define __rcu address space modifier for sparse · ca5ecddf
      Paul E. McKenney authored
      This commit provides definitions for the __rcu annotation defined earlier.
      This annotation permits sparse to check for correct use of RCU-protected
      pointers.  If a pointer that is annotated with __rcu is accessed
      directly (as opposed to via rcu_dereference(), rcu_assign_pointer(),
      or one of their variants), sparse can be made to complain.  To enable
      such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER
      kernel configuration option.  Please note that these sparse complaints are
      intended to be a debugging aid, -not- a code-style-enforcement mechanism.
      
      There are special rcu_dereference_protected() and rcu_access_pointer()
      accessors for use when RCU read-side protection is not required, for
      example, when no other CPU has access to the data structure in question
      or while the current CPU hold the update-side lock.
      
      This patch also updates a number of docbook comments that were showing
      their age.
      Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Christopher Li <sparse@chrisli.org>
      Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
      ca5ecddf
  3. 10 May, 2010 2 commits
  4. 25 Feb, 2010 2 commits
    • Paul E. McKenney's avatar
      rcu: Add lockdep-enabled variants of rcu_dereference() · c26d34a5
      Paul E. McKenney authored
      Make rcu_dereference() check for being in an RCU read-side
      critical section, and create rcu_dereference_bh(),
      rcu_dereference_sched(), and srcu_dereference() to check for the
      other flavors of RCU.  Also create rcu_dereference_raw() to
      avoid checking, and make rcu_dereference_check() use
      rcu_dereference_raw().
      Acked-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <1266887105-1528-2-git-send-email-paulmck@linux.vnet.ibm.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      c26d34a5
    • Paul E. McKenney's avatar
      rcu: Introduce lockdep-based checking to RCU read-side primitives · 632ee200
      Paul E. McKenney authored
      Inspection is proving insufficient to catch all RCU misuses,
      which is understandable given that rcu_dereference() might be
      protected by any of four different flavors of RCU (RCU, RCU-bh,
      RCU-sched, and SRCU), and might also/instead be protected by any
      of a number of locking primitives. It is therefore time to
      enlist the aid of lockdep.
      
      This set of patches is inspired by earlier work by Peter
      Zijlstra and Thomas Gleixner, and takes the following approach:
      
      o	Set up separate lockdep classes for RCU, RCU-bh, and RCU-sched.
      
      o	Set up separate lockdep classes for each instance of SRCU.
      
      o	Create primitives that check for being in an RCU read-side
      	critical section.  These return exact answers if lockdep is
      	fully enabled, but if unsure, report being in an RCU read-side
      	critical section.  (We want to avoid false positives!)
      	The primitives are:
      
      	For RCU: rcu_read_lock_held(void)
      
      	For RCU-bh: rcu_read_lock_bh_held(void)
      
      	For RCU-sched: rcu_read_lock_sched_held(void)
      
      	For SRCU: srcu_read_lock_held(struct srcu_struct *sp)
      
      o	Add rcu_dereference_check(), which takes a second argument
      	in which one places a boolean expression based on the above
      	primitives and/or lockdep_is_held().
      
      o	A new kernel configuration parameter, CONFIG_PROVE_RCU, enables
      	rcu_dereference_check().  This depends on CONFIG_PROVE_LOCKING,
      	and should be quite helpful during the transition period while
      	CONFIG_PROVE_RCU-unaware patches are in flight.
      
      The existing rcu_dereference() primitive does no checking, but
      upcoming patches will change that.
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: laijs@cn.fujitsu.com
      Cc: dipankar@in.ibm.com
      Cc: mathieu.desnoyers@polymtl.ca
      Cc: josh@joshtriplett.org
      Cc: dvhltc@us.ibm.com
      Cc: niv@us.ibm.com
      Cc: peterz@infradead.org
      Cc: rostedt@goodmis.org
      Cc: Valdis.Kletnieks@vt.edu
      Cc: dhowells@redhat.com
      LKML-Reference: <1266887105-1528-1-git-send-email-paulmck@linux.vnet.ibm.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      632ee200
  5. 16 Feb, 2010 1 commit
  6. 26 Oct, 2009 1 commit
  7. 04 Oct, 2006 3 commits
    • Alan Stern's avatar
      [PATCH] SRCU: report out-of-memory errors · e6a92013
      Alan Stern authored
      Currently the init_srcu_struct() routine has no way to report out-of-memory
      errors.  This patch (as761) makes it return -ENOMEM when the per-cpu data
      allocation fails.
      
      The patch also makes srcu_init_notifier_head() report a BUG if a notifier
      head can't be initialized.  Perhaps it should return -ENOMEM instead, but
      in the most likely cases where this might occur I don't think any recovery
      is possible.  Notifier chains generally are not created dynamically.
      
      [akpm@osdl.org: avoid statement-with-side-effect in macro]
      Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
      Acked-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      e6a92013
    • Alan Stern's avatar
      [PATCH] Add SRCU-based notifier chains · eabc0694
      Alan Stern authored
      This patch (as751) adds a new type of notifier chain, based on the SRCU
      (Sleepable Read-Copy Update) primitives recently added to the kernel.  An
      SRCU notifier chain is much like a blocking notifier chain, in that it must
      be called in process context and its callout routines are allowed to sleep.
       The difference is that the chain's links are protected by the SRCU
      mechanism rather than by an rw-semaphore, so calling the chain has
      extremely low overhead: no memory barriers and no cache-line bouncing.  On
      the other hand, unregistering from the chain is expensive and the chain
      head requires special runtime initialization (plus cleanup if it is to be
      deallocated).
      
      SRCU notifiers are appropriate for notifiers that will be called very
      frequently and for which unregistration occurs very seldom.  The proposed
      "task notifier" scheme qualifies, as may some of the network notifiers.
      Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
      Acked-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
      Acked-by: default avatarChandra Seetharaman <sekharan@us.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      eabc0694
    • Paul E. McKenney's avatar
      [PATCH] srcu-3: RCU variant permitting read-side blocking · 621934ee
      Paul E. McKenney authored
      Updated patch adding a variant of RCU that permits sleeping in read-side
      critical sections.  SRCU is as follows:
      
      o	Each use of SRCU creates its own srcu_struct, and each
      	srcu_struct has its own set of grace periods.  This is
      	critical, as it prevents one subsystem with a blocking
      	reader from holding up SRCU grace periods for other
      	subsystems.
      
      o	The SRCU primitives (srcu_read_lock(), srcu_read_unlock(),
      	and synchronize_srcu()) all take a pointer to a srcu_struct.
      
      o	The SRCU primitives must be called from process context.
      
      o	srcu_read_lock() returns an int that must be passed to
      	the matching srcu_read_unlock().  Realtime RCU avoids the
      	need for this by storing the state in the task struct,
      	but SRCU needs to allow a given code path to pass through
      	multiple SRCU domains -- storing state in the task struct
      	would therefore require either arbitrary space in the
      	task struct or arbitrary limits on SRCU nesting.  So I
      	kicked the state-storage problem up to the caller.
      
      	Of course, it is not permitted to call synchronize_srcu()
      	while in an SRCU read-side critical section.
      
      o	There is no call_srcu().  It would not be hard to implement
      	one, but it seems like too easy a way to OOM the system.
      	(Hey, we have enough trouble with call_rcu(), which does
      	-not- permit readers to sleep!!!)  So, if you want it,
      	please tell me why...
      
      [josht@us.ibm.com: sparse notation]
      Signed-off-by: default avatarPaul E. McKenney <paulmck@us.ibm.com>
      Signed-off-by: default avatarJosh Triplett <josh@freedesktop.org>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      621934ee