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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-04-20 09:22:54 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-06-14 16:00:59 -0700 |
commit | c79dac758dc59f7461a721aaf65301cde8a448bc (patch) | |
tree | 69e221f9ec759a233ed1dfdee08a3f8133b4c401 /Documentation | |
parent | db4855b5a88535746558fb756512090fc1ce5607 (diff) | |
download | linux-c79dac758dc59f7461a721aaf65301cde8a448bc.tar.gz linux-c79dac758dc59f7461a721aaf65301cde8a448bc.tar.bz2 linux-c79dac758dc59f7461a721aaf65301cde8a448bc.zip |
documentation: Add RCU_NONIDLE() restrictions to requirements
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.html | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index e7e24b3e86e2..ece410f40436 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -2391,6 +2391,41 @@ and <tt>RCU_NONIDLE()</tt> on the other while inspecting idle-loop code. Steven Rostedt supplied <tt>_rcuidle</tt> event tracing, which is used quite heavily in the idle loop. +However, there are some restrictions on the code placed within +<tt>RCU_NONIDLE()</tt>: + +<ol> +<li> Blocking is prohibited. + In practice, this is not a serious restriction given that idle + tasks are prohibited from blocking to begin with. +<li> Although nesting <tt>RCU_NONIDLE()</tt> is permited, they cannot + nest indefinitely deeply. + However, given that they can be nested on the order of a million + deep, even on 32-bit systems, this should not be a serious + restriction. + This nesting limit would probably be reached long after the + compiler OOMed or the stack overflowed. +<li> Any code path that enters <tt>RCU_NONIDLE()</tt> must sequence + out of that same <tt>RCU_NONIDLE()</tt>. + For example, the following is grossly illegal: + + <blockquote> + <pre> + 1 RCU_NONIDLE({ + 2 do_something(); + 3 goto bad_idea; /* BUG!!! */ + 4 do_something_else();}); + 5 bad_idea: + </pre> + </blockquote> + + <p> + It is just as illegal to transfer control into the middle of + <tt>RCU_NONIDLE()</tt>'s argument. + Yes, in theory, you could transfer in as long as you also + transferred out, but in practice you could also expect to get sharply + worded review comments. +</ol> <p> It is similarly socially unacceptable to interrupt an |