The following commit has been merged into the core/rcu branch of tip: Commit-ID: 9d3a04853fe640e0eba2c0799c880b7dcf190219 Gitweb: https://git.kernel.org/tip/9d3a04853fe640e0eba2c0799c880b7dcf190219 Author: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx> AuthorDate: Sat, 28 Nov 2020 15:32:59 -05:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Mon, 04 Jan 2021 13:35:14 -08:00 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@xxxxxxxxxxxxxxxxxx/ Cc: Michael Opdenacker <michael.opdenacker@xxxxxxxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- Documentation/RCU/Design/Requirements/Requirements.rst | 23 ++++----- Documentation/RCU/checklist.rst | 8 +-- 2 files changed, 14 insertions(+), 17 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index 1e3df77..f32f8fa 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -321,11 +321,10 @@ do_something_gp_buggy() below: 12 } However, this temptation must be resisted because there are a -surprisingly large number of ways that the compiler (to say nothing of -`DEC Alpha CPUs <https://h71000.www7.hp.com/wizard/wiz_2637.html>`__) -can trip this code up. For but one example, if the compiler were short -of registers, it might choose to refetch from ``gp`` rather than keeping -a separate copy in ``p`` as follows: +surprisingly large number of ways that the compiler (or weak ordering +CPUs like the DEC Alpha) can trip this code up. For but one example, if +the compiler were short of registers, it might choose to refetch from +``gp`` rather than keeping a separate copy in ``p`` as follows: :: @@ -1183,7 +1182,7 @@ costs have plummeted. However, as I learned from Matt Mackall's `bloatwatch <http://elinux.org/Linux_Tiny-FAQ>`__ efforts, memory footprint is critically important on single-CPU systems with non-preemptible (``CONFIG_PREEMPT=n``) kernels, and thus `tiny -RCU <https://lkml.kernel.org/g/20090113221724.GA15307@xxxxxxxxxxxxxxxxxx>`__ +RCU <https://lore.kernel.org/r/20090113221724.GA15307@xxxxxxxxxxxxxxxxxx>`__ was born. Josh Triplett has since taken over the small-memory banner with his `Linux kernel tinification <https://tiny.wiki.kernel.org/>`__ project, which resulted in `SRCU <#Sleepable%20RCU>`__ becoming optional @@ -1624,7 +1623,7 @@ against mishaps and misuse: init_rcu_head() and cleaned up with destroy_rcu_head(). Mathieu Desnoyers made me aware of this requirement, and also supplied the needed - `patch <https://lkml.kernel.org/g/20100319013024.GA28456@Krystal>`__. + `patch <https://lore.kernel.org/r/20100319013024.GA28456@Krystal>`__. #. An infinite loop in an RCU read-side critical section will eventually trigger an RCU CPU stall warning splat, with the duration of “eventually” being controlled by the ``RCU_CPU_STALL_TIMEOUT`` @@ -1716,7 +1715,7 @@ requires almost all of them be hidden behind a ``CONFIG_RCU_EXPERT`` This all should be quite obvious, but the fact remains that Linus Torvalds recently had to -`remind <https://lkml.kernel.org/g/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@xxxxxxxxxxxxxx>`__ +`remind <https://lore.kernel.org/r/CA+55aFy4wcCwaL4okTs8wXhGZ5h-ibecy_Meg9C4MNQrUnwMcg@xxxxxxxxxxxxxx>`__ me of this requirement. Firmware Interface @@ -1837,9 +1836,9 @@ NMI handlers. The name notwithstanding, some Linux-kernel architectures can have nested NMIs, which RCU must handle correctly. Andy Lutomirski `surprised -me <https://lkml.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@xxxxxxxxxxxxxx>`__ +me <https://lore.kernel.org/r/CALCETrXLq1y7e_dKFPgou-FKHB6Pu-r8+t-6Ds+8=va7anBWDA@xxxxxxxxxxxxxx>`__ with this requirement; he also kindly surprised me with `an -algorithm <https://lkml.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@xxxxxxxxxxxxxx>`__ +algorithm <https://lore.kernel.org/r/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@xxxxxxxxxxxxxx>`__ that meets this requirement. Furthermore, NMI handlers can be interrupted by what appear to RCU to be @@ -2264,7 +2263,7 @@ more extreme measures. Returning to the ``page`` structure, the ``rcu_head`` field shares storage with a great many other structures that are used at various points in the corresponding page's lifetime. In order to correctly resolve certain `race -conditions <https://lkml.kernel.org/g/1439976106-137226-1-git-send-email-kirill.shutemov@xxxxxxxxxxxxxxx>`__, +conditions <https://lore.kernel.org/r/1439976106-137226-1-git-send-email-kirill.shutemov@xxxxxxxxxxxxxxx>`__, the Linux kernel's memory-management subsystem needs a particular bit to remain zero during all phases of grace-period processing, and that bit happens to map to the bottom bit of the ``rcu_head`` structure's @@ -2328,7 +2327,7 @@ preempted. This requirement made its presence known after users made it clear that an earlier `real-time patch <https://lwn.net/Articles/107930/>`__ did not meet their needs, in conjunction with some `RCU -issues <https://lkml.kernel.org/g/20050318002026.GA2693@xxxxxxxxxx>`__ +issues <https://lore.kernel.org/r/20050318002026.GA2693@xxxxxxxxxx>`__ encountered by a very early version of the -rt patchset. In addition, RCU must make do with a sub-100-microsecond real-time diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index bb7128e..2d1dc1d 100644 --- a/Documentation/RCU/checklist.rst +++ b/Documentation/RCU/checklist.rst @@ -70,7 +70,7 @@ over a rather long period of time, but improvements are always welcome! is less readable and prevents lockdep from detecting locking issues. Letting RCU-protected pointers "leak" out of an RCU read-side - critical section is every bid as bad as letting them leak out + critical section is every bit as bad as letting them leak out from under a lock. Unless, of course, you have arranged some other means of protection, such as a lock or a reference count -before- letting them out of the RCU read-side critical section. @@ -129,9 +129,7 @@ over a rather long period of time, but improvements are always welcome! accesses. The rcu_dereference() primitive ensures that the CPU picks up the pointer before it picks up the data that the pointer points to. This really is necessary - on Alpha CPUs. If you don't believe me, see: - - http://www.openvms.compaq.com/wizard/wiz_2637.html + on Alpha CPUs. The rcu_dereference() primitive is also an excellent documentation aid, letting the person reading the @@ -216,7 +214,7 @@ over a rather long period of time, but improvements are always welcome! 7. As of v4.20, a given kernel implements only one RCU flavor, which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y. If the updater uses call_rcu() or synchronize_rcu(), - then the corresponding readers my use rcu_read_lock() and + then the corresponding readers may use rcu_read_lock() and rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(), or any pair of primitives that disables and re-enables preemption, for example, rcu_read_lock_sched() and rcu_read_unlock_sched().
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