[RFC][PATCH 0/5] Introduce checks for preemptable code for this_cpu_read/write()

Steven Rostedt
2011-09-19T21:26:48Z

I just found out that the this_cpu_*() functions do not perform the
test to see if the usage is in atomic or not. Thus, the blind
conversion of the per_cpu(*, smp_processor_id()) and the get_cpu_var()
code to this_cpu_*() introduce the regression to detect the hard
to find case where a per cpu variable is used in preempt code that
migrates and causes bugs.

I'm adding back a simple call to smp_processor_id() to
this_cpu_read() and this_cpu_write() to see what errors I find.
I found 4 places that required touch up. 3 were areas that the race
is known and we don't care, but the memcg looks very buggy.

Anyway, if I had known that the this_cpu_*() code removed this
smp_processor_id() check, I would have NAK'd all the changes to the tracing
code.

I only modified this_cpu_read and *_write() I may decide other this_cpu_*
code should be updated too. Especially the ones that return a value.

-- Steve

Steven Rostedt (5):
x86: Remove const_udelay() caring about which cpu var it uses
mm: Switch mod_state() to __this_cpu_read()
memcg: Disable preemption in memcg_check_events()
printk: Have wake_up_klogd() use __this_cpu_write()
percpu: Add preempt checks back into this_cpu_read/write()

----
arch/x86/lib/delay.c | 2 +-
include/linux/percpu.h | 17 +++++++++++++++--
kernel/printk.c | 2 +-
mm/memcontrol.c | 2 ++
mm/vmstat.c | 4 ++--
5 files changed, 21 insertions(+), 6 deletions(-)