Eric Lee / smarc-ti-linux-kernel

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Commit c17ac85504efec5f3a9b0c5b05bffd6f30e5b655

Authored by Paul E. McKenney
Committed by Linus Torvalds
1 parent b2d9323d13
Exists in master and in 20 other branches dlt-processor-sdk-linux-03.00.00.04, newt-ti-linux-3.12.y, processor-sdk-linux-01.00.00, processor-sdk-linux-02.00.01, smarc-ti-linux-3.12.10, smarc-ti-linux-3.12.y, smarc-ti-linux-3.14.y, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.12.y, ti-linux-3.14.y, ti-linux-3.15.y, ti-lsk-linux-4.1.y

Make rcutorture RNG use temporal entropy 

Repost of http://lkml.org/lkml/2007/8/10/472 made available by request.

The locking used by get_random_bytes() can conflict with the
preempt_disable() and synchronize_sched() form of RCU.  This patch changes
rcutorture's RNG to gather entropy from the new cpu_clock() interface
(relying on interrupts, preemption, daemons, and rcutorture's reader
thread's rock-bottom scheduling priority to provide useful entropy), and
also adds and EXPORT_SYMBOL_GPL() to make that interface available to GPLed
kernel modules such as rcutorture.

Passes several hours of rcutorture.

[ego@in.ibm.com: Use raw_smp_processor_id() in rcu_random()]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 3 additions and 6 deletions Side-by-side Diff

... ... @@ -41,7 +41,6 @@
41 41 #include <linux/notifier.h>
42 42 #include <linux/freezer.h>
43 43 #include <linux/cpu.h>
44   -#include <linux/random.h>
45 44 #include <linux/delay.h>
46 45 #include <linux/byteorder/swabb.h>
47 46 #include <linux/stat.h>
48 47  
49 48  
... ... @@ -165,16 +164,14 @@
165 164  
166 165 /*
167 166 * Crude but fast random-number generator. Uses a linear congruential
168   - * generator, with occasional help from get_random_bytes().
  167 + * generator, with occasional help from cpu_clock().
169 168 */
170 169 static unsigned long
171 170 rcu_random(struct rcu_random_state *rrsp)
172 171 {
173   - long refresh;
174   -
175 172 if (--rrsp->rrs_count < 0) {
176   - get_random_bytes(&refresh, sizeof(refresh));
177   - rrsp->rrs_state += refresh;
  173 + rrsp->rrs_state +=
  174 + (unsigned long)cpu_clock(raw_smp_processor_id());
178 175 rrsp->rrs_count = RCU_RANDOM_REFRESH;
179 176 }
180 177 rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;