UBIFS: improve power cut emulation testing

This patch cleans-up and improves the power cut testing:

1. Kill custom 'simple_random()' function and use 'random32()' instead.
2. Make timeout larger
3. When cutting the buffer - fill the end with random data sometimes, not
   only with 0xFFs.
4. Some times cut in the middle of the buffer, not always at the end.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 50 insertions, 41 deletions

diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
index b801af7837e9..eef109a1a927 100644
--- a/fs/ubifs/debug.c
+++ b/fs/ubifs/debug.c
@@ -27,11 +27,12 @@
  * various local functions of those subsystems.
  */
 
-#include "ubifs.h"
 #include <linux/module.h>
 #include <linux/debugfs.h>
 #include <linux/math64.h>
 #include <linux/uaccess.h>
+#include <linux/random.h>
+#include "ubifs.h"
 
 #ifdef CONFIG_UBIFS_FS_DEBUG
 
@@ -2535,17 +2536,10 @@ error_dump:
         return 0;
 }
 
-/* Failure mode for recovery testing */
-
-#define chance(n, d) (simple_rand() <= (n) * 32768LL / (d))
-
-static unsigned int next;
-static int simple_rand(void)
+static inline int chance(unsigned int n, unsigned int out_of)
 {
-        if (next == 0)
-                next = current->pid;
-        next = next * 1103515245 + 12345;
-        return (next >> 16) & 32767;
+        return !!((random32() % out_of) + 1 <= n);
+
 }
 
 static int power_cut_emulated(struct ubifs_info *c, int lnum, int write)
@@ -2557,33 +2551,37 @@ static int power_cut_emulated(struct ubifs_info *c, int lnum, int write)
         if (!d->pc_cnt) {
                 /* First call - decide delay to the power cut */
                 if (chance(1, 2)) {
-                        unsigned int delay = 1 << (simple_rand() >> 11);
+                        unsigned long delay;
 
                         if (chance(1, 2)) {
                                 d->pc_delay = 1;
-                                d->pc_timeout = jiffies +
-                                                  msecs_to_jiffies(delay);
-                                ubifs_warn("failing after %ums", delay);
+                                /* Fail withing 1 minute */
+                                delay = random32() % 60000;
+                                d->pc_timeout = jiffies;
+                                d->pc_timeout += msecs_to_jiffies(delay);
+                                ubifs_warn("failing after %lums", delay);
                         } else {
                                 d->pc_delay = 2;
+                                delay = random32() % 10000;
+                                /* Fail within 10000 operations */
                                 d->pc_cnt_max = delay;
-                                ubifs_warn("failing after %u calls", delay);
+                                ubifs_warn("failing after %lu calls", delay);
                         }
                 }
+
                 d->pc_cnt += 1;
         }
+
         /* Determine if failure delay has expired */
-        if (d->pc_delay == 1) {
-                if (time_before(jiffies, d->pc_timeout))
+        if (d->pc_delay == 1 && time_before(jiffies, d->pc_timeout))
                         return 0;
-        } else if (d->pc_delay == 2)
-                if (d->pc_cnt++ < d->pc_cnt_max)
+        if (d->pc_delay == 2 && d->pc_cnt++ < d->pc_cnt_max)
                         return 0;
+
         if (lnum == UBIFS_SB_LNUM) {
-                if (write) {
-                        if (chance(1, 2))
-                                return 0;
-                } else if (chance(19, 20))
+                if (write && chance(1, 2))
+                        return 0;
+                if (chance(19, 20))
                         return 0;
                 ubifs_warn("failing in super block LEB %d", lnum);
         } else if (lnum == UBIFS_MST_LNUM || lnum == UBIFS_MST_LNUM + 1) {
@@ -2591,24 +2589,21 @@ static int power_cut_emulated(struct ubifs_info *c, int lnum, int write)
                         return 0;
                 ubifs_warn("failing in master LEB %d", lnum);
         } else if (lnum >= UBIFS_LOG_LNUM && lnum <= c->log_last) {
-                if (write) {
-                        if (chance(99, 100))
-                                return 0;
-                } else if (chance(399, 400))
+                if (write && chance(99, 100))
+                        return 0;
+                if (chance(399, 400))
                         return 0;
                 ubifs_warn("failing in log LEB %d", lnum);
         } else if (lnum >= c->lpt_first && lnum <= c->lpt_last) {
-                if (write) {
-                        if (chance(7, 8))
-                                return 0;
-                } else if (chance(19, 20))
+                if (write && chance(7, 8))
+                        return 0;
+                if (chance(19, 20))
                         return 0;
                 ubifs_warn("failing in LPT LEB %d", lnum);
         } else if (lnum >= c->orph_first && lnum <= c->orph_last) {
-                if (write) {
-                        if (chance(1, 2))
-                                return 0;
-                } else if (chance(9, 10))
+                if (write && chance(1, 2))
+                        return 0;
+                if (chance(9, 10))
                         return 0;
                 ubifs_warn("failing in orphan LEB %d", lnum);
         } else if (lnum == c->ihead_lnum) {
@@ -2636,18 +2631,32 @@ static int power_cut_emulated(struct ubifs_info *c, int lnum, int write)
         }
 
         d->pc_happened = 1;
+        ubifs_warn("========== Power cut emulated ==========");
         dump_stack();
         return 1;
 }
 
-static void cut_data(const void *buf, int len)
+static void cut_data(const void *buf, unsigned int len)
 {
-        int flen, i;
+        unsigned int from, to, i, ffs = chance(1, 2);
         unsigned char *p = (void *)buf;
 
-        flen = (len * (long long)simple_rand()) >> 15;
-        for (i = flen; i < len; i++)
-                p[i] = 0xff;
+        from = random32() % (len + 1);
+        if (chance(1, 2))
+                to = random32() % (len - from + 1);
+        else
+                to = len;
+
+        if (from < to)
+                ubifs_warn("filled bytes %u-%u with %s", from, to - 1,
+                           ffs ? "0xFFs" : "random data");
+
+        if (ffs)
+                for (i = from; i < to; i++)
+                        p[i] = 0xFF;
+        else
+                for (i = from; i < to; i++)
+                        p[i] = random32() % 0x100;
 }
 
 int dbg_leb_write(struct ubifs_info *c, int lnum, const void *buf,