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docs: Fix typos and drop/fix dead links in RCU documentation
It appears the Compaq link moved to a machine at HP for a while after the merger of the two, but that doesn't work either. A search of HP for "wiz_2637" (w and w/o html suffix) comes up empty. Since the references aren't critical to the documents we remove them. Also, the lkml.kernel.org/g links have been broken for ages, so replace them with lore.kernel.org/r links - standardize on lore for all links too. Note that we put off fixing these 4y ago - presumably thinking that a treewide fixup was pending. Probably safe to go fix the RCU ones now. https://lore.kernel.org/r/20160915144926.GD10850@linux.vnet.ibm.com/ Cc: Michael Opdenacker <michael.opdenacker@free-electrons.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Paul Gortmaker
Paul E. McKenney
parent
4704bd3171
commit
9d3a04853f
@ -321,11 +321,10 @@ do_something_gp_buggy() below:
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12 }
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However, this temptation must be resisted because there are a
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surprisingly large number of ways that the compiler (to say nothing of
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`DEC Alpha CPUs <https://h71000.www7.hp.com/wizard/wiz_2637.html>`__)
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can trip this code up. For but one example, if the compiler were short
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of registers, it might choose to refetch from ``gp`` rather than keeping
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a separate copy in ``p`` as follows:
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surprisingly large number of ways that the compiler (or weak ordering
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CPUs like the DEC Alpha) can trip this code up. For but one example, if
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the compiler were short of registers, it might choose to refetch from
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``gp`` rather than keeping a separate copy in ``p`` as follows:
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::
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@ -1183,7 +1182,7 @@ costs have plummeted. However, as I learned from Matt Mackall's
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`bloatwatch <http://elinux.org/Linux_Tiny-FAQ>`__ efforts, memory
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footprint is critically important on single-CPU systems with
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non-preemptible (``CONFIG_PREEMPT=n``) kernels, and thus `tiny
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RCU <https://lkml.kernel.org/g/20090113221724.GA15307@linux.vnet.ibm.com>`__
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RCU <https://lore.kernel.org/r/20090113221724.GA15307@linux.vnet.ibm.com>`__
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was born. Josh Triplett has since taken over the small-memory banner
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with his `Linux kernel tinification <https://tiny.wiki.kernel.org/>`__
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project, which resulted in `SRCU <#Sleepable%20RCU>`__ becoming optional
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@ -1624,7 +1623,7 @@ against mishaps and misuse:
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init_rcu_head() and cleaned up with destroy_rcu_head().
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Mathieu Desnoyers made me aware of this requirement, and also
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supplied the needed
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`patch <https://lkml.kernel.org/g/20100319013024.GA28456@Krystal>`__.
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`patch <https://lore.kernel.org/r/20100319013024.GA28456@Krystal>`__.
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#. An infinite loop in an RCU read-side critical section will eventually
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trigger an RCU CPU stall warning splat, with the duration of
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“eventually” being controlled by the ``RCU_CPU_STALL_TIMEOUT``
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@ -1716,7 +1715,7 @@ requires almost all of them be hidden behind a ``CONFIG_RCU_EXPERT``
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This all should be quite obvious, but the fact remains that Linus
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Torvalds recently had to
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`remind <https://lkml.kernel.org/g/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@mail.gmail.com>`__
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`remind <https://lore.kernel.org/r/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@mail.gmail.com>`__
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me of this requirement.
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Firmware Interface
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@ -1837,9 +1836,9 @@ NMI handlers.
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The name notwithstanding, some Linux-kernel architectures can have
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nested NMIs, which RCU must handle correctly. Andy Lutomirski `surprised
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me <https://lkml.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@mail.gmail.com>`__
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me <https://lore.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@mail.gmail.com>`__
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with this requirement; he also kindly surprised me with `an
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algorithm <https://lkml.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@mail.gmail.com>`__
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algorithm <https://lore.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@mail.gmail.com>`__
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that meets this requirement.
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Furthermore, NMI handlers can be interrupted by what appear to RCU to be
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@ -2264,7 +2263,7 @@ more extreme measures. Returning to the ``page`` structure, the
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``rcu_head`` field shares storage with a great many other structures
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that are used at various points in the corresponding page's lifetime. In
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order to correctly resolve certain `race
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conditions <https://lkml.kernel.org/g/1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com>`__,
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conditions <https://lore.kernel.org/r/1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com>`__,
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the Linux kernel's memory-management subsystem needs a particular bit to
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remain zero during all phases of grace-period processing, and that bit
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happens to map to the bottom bit of the ``rcu_head`` structure's
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@ -2328,7 +2327,7 @@ preempted. This requirement made its presence known after users made it
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clear that an earlier `real-time
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patch <https://lwn.net/Articles/107930/>`__ did not meet their needs, in
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conjunction with some `RCU
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issues <https://lkml.kernel.org/g/20050318002026.GA2693@us.ibm.com>`__
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issues <https://lore.kernel.org/r/20050318002026.GA2693@us.ibm.com>`__
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encountered by a very early version of the -rt patchset.
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In addition, RCU must make do with a sub-100-microsecond real-time
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@ -70,7 +70,7 @@ over a rather long period of time, but improvements are always welcome!
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is less readable and prevents lockdep from detecting locking issues.
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Letting RCU-protected pointers "leak" out of an RCU read-side
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critical section is every bid as bad as letting them leak out
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critical section is every bit as bad as letting them leak out
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from under a lock. Unless, of course, you have arranged some
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other means of protection, such as a lock or a reference count
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-before- letting them out of the RCU read-side critical section.
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@ -129,9 +129,7 @@ over a rather long period of time, but improvements are always welcome!
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accesses. The rcu_dereference() primitive ensures that
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the CPU picks up the pointer before it picks up the data
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that the pointer points to. This really is necessary
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on Alpha CPUs. If you don't believe me, see:
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http://www.openvms.compaq.com/wizard/wiz_2637.html
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on Alpha CPUs.
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The rcu_dereference() primitive is also an excellent
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documentation aid, letting the person reading the
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@ -216,7 +214,7 @@ over a rather long period of time, but improvements are always welcome!
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7. As of v4.20, a given kernel implements only one RCU flavor,
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which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y.
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If the updater uses call_rcu() or synchronize_rcu(),
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then the corresponding readers my use rcu_read_lock() and
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then the corresponding readers may use rcu_read_lock() and
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rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(),
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or any pair of primitives that disables and re-enables preemption,
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for example, rcu_read_lock_sched() and rcu_read_unlock_sched().
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