lkml.org 
[lkml]   [2015]   [Oct]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock()
    On Tue, Oct 06, 2015 at 10:36:46AM -0700, Paul E. McKenney wrote:
    > On Tue, Oct 06, 2015 at 10:18:39AM -0700, Josh Triplett wrote:
    > > On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote:
    > > > Currently, __srcu_read_lock() cannot be invoked from restricted
    > > > environments because it contains calls to preempt_disable() and
    > > > preempt_enable(), both of which can invoke lockdep, which is a bad
    > > > idea in some restricted execution modes. This commit therefore moves
    > > > the preempt_disable() and preempt_enable() from __srcu_read_lock()
    > > > to srcu_read_lock(). It also inserts the preempt_disable() and
    > > > preempt_enable() around the call to __srcu_read_lock() in do_exit().
    > >
    > > What restricted environments do you intend to invoke
    > > __srcu_read_lock from?
    > >
    > > This change seems fine, but I don't see any change in this patch series
    > > that needs this, hence my curiosity.
    >
    > Someone asked me for it, and now I cannot find it. :-(
    >
    > Something to the effect of when running unmapped during exception entry
    > or something like that. I guess one way to find out would be to remove
    > the commit and see who complained, but on the other hand, it arguably
    > makes more sense to have only the bare mechanism is __srcu_read_lock()
    > and put the environmental protection into srcu_read_lock().

    I agree; I just find the idea that someone would need to call
    __srcu_read_lock rather than srcu_read_lock odd and worthy of further
    understanding. :)


    \
     
     \ /
      Last update: 2015-10-06 20:01    [W:4.164 / U:0.024 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site