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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2008-03-19 17:00:57 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-03-19 18:53:36 -0700 |
commit | ae66be9b71b12f16b84129860d06bbfe37fbec51 (patch) | |
tree | 5bf1d1722f0d83bb4c30621b031437a141a15af1 /fs/compat_ioctl.c | |
parent | b691da35ba94d5fa0a32589d99b6546be2bf4cfa (diff) |
rcu: fix misplaced mb() in rcu_enter/exit_nohz()
In the process of writing up the mechanical proof of correctness for the
dynticks/preemptable-RCU interface, I noticed misplaced memory barriers in
rcu_enter_nohz() and rcu_exit_nohz().
This patch puts them in the right place and adds a comment. The key thing to
keep in mind is that rcu_enter_nohz() is -exiting- the mode that can legally
execute RCU read-side critical sections.
The memory barrier must be between any potential RCU read-side critical
sections and the increment of the per-CPU dynticks_progress_counter, and thus
must come -before- this increment. And vice versa for rcu_exit_nohz().
The locking in the scheduler is probably saving us for the moment.
Also, switch to smp_mb() - we don't need a barrier for uniprocessor kernels.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/compat_ioctl.c')
0 files changed, 0 insertions, 0 deletions