>From 52f5d218442eb64f2798335d56a1838f90d96d5f Mon Sep 17 00:00:00 2001
From: Akira Yokosawa <akiyks@xxxxxxxxx>
Date: Mon, 30 Dec 2018 22:54:43 +0900
Subject: [PATCH] EXP hashtorture.h: Avoid sporadic SIGSEGV in hash_bkt_rcu
Commit 4e22bdc905ff ("Wait at end of test for call_rcu() to finish")
added a couple of synchronize_rcu()s in perftest_update()
and zoo_reader().
However, there still remains sporadic SIGSEGV in
$ ./hash_bkt_rcu --perftest --nupdaters 3
On the other hand,
$ ./hash_bkt_rcu --schroedinger --nupdaters 3
does not show such issue. Just moving synchronize_rcu()s in
zoo_reader() to zoo_updater() does not resolve the
SIGSEGV.
This commit defines rcu_barrier() if not available,
and puts them at both before and after the final loop
of perftest_updater() and zoo_updater().
It looks like this change can fix the above mentioned
SIGSEGV in "--perftest".
[Tested on Ubuntu Xenial with liburcu-dev/xenial,now 0.9.1-3 and
liburcu4/xenial,now 0.9.1-3 installed.]
NOTE:
$ ./hash_resize --schroedinger --resizemult 2 --duration 20
still fails with SIGSEGV frequently in zoo_del(). GDB says:
(gdb) where
#0 0x0000000000402b27 in cds_list_del_rcu (elem=0x7ff8fc0138f0)
at /usr/include/urcu/rculist.h:71
#1 hashtab_del (htep=0x7ff8fc0138d0, htp_master=<optimized out>)
at hash_resize.c:261
#2 zoo_del (zhep=0x7ff8fc0138d0) at hashtorture.h:1007
#3 zoo_updater (arg=0x1e8b298) at hashtorture.h:1153
#4 0x00007ff9057d16ba in start_thread (arg=0x7ff903fed700)
at pthread_create.c:333
#5 0x00007ff9050f741d in clone ()
at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
Hi Paul,
This is a partial fix, but it resolves SIGSEGV in "--perftest" of
hash_bkt_rcu and hash_resize.
"--schroedinger" of hash_resize with resizing enabled still seg faults
as mentioned in the commit log.
By the way, what version of liburcu are you using?
Thanks, Akira
--
CodeSamples/datastruct/hash/hashtorture.h | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/CodeSamples/datastruct/hash/hashtorture.h b/CodeSamples/datastruct/hash/hashtorture.h
index 0e90220..9ae3dfa 100644
--- a/CodeSamples/datastruct/hash/hashtorture.h
+++ b/CodeSamples/datastruct/hash/hashtorture.h
@@ -55,6 +55,15 @@ void (*defer_del_done)(struct ht_elem *htep) = NULL;
#ifndef quiescent_state
#define quiescent_state() do ; while (0)
#define synchronize_rcu() do ; while (0)
+#define rcu_barrier() do ; while (0)
+#else
+#ifndef rcu_barrier
+#define rcu_barrier() do { \
+ synchronize_rcu(); \
+ poll(NULL, 0, 100); \
+ synchronize_rcu(); \
+ } while (0)
+#endif /* #ifndef rcu_barrier */
#endif /* #ifndef quiescent_state */
/*
@@ -765,6 +774,7 @@ void *perftest_reader(void *arg)
if (i >= ne)
i = i % ne + offset;
}
+
pap->nlookups = nlookups;
pap->nlookupfails = nlookupfails;
hash_unregister_thread();
@@ -839,6 +849,7 @@ void *perftest_updater(void *arg)
quiescent_state();
}
+ rcu_barrier();
/* Test over, so remove all our elements from the hash table. */
for (i = 0; i < elperupdater; i++) {
if (thep[i].in_table != 1)
@@ -846,10 +857,7 @@ void *perftest_updater(void *arg)
BUG_ON(!perftest_lookup(thep[i].data));
perftest_del(&thep[i]);
}
- /* Really want rcu_barrier(), but missing from old liburcu versions. */
- synchronize_rcu();
- poll(NULL, 0, 100);
- synchronize_rcu();
+ rcu_barrier();
hash_unregister_thread();
free(thep);
@@ -1048,10 +1056,6 @@ void *zoo_reader(void *arg)
if (i >= ne)
i = i % ne + offset;
}
- /* Really want rcu_barrier(), but missing from old liburcu versions. */
- synchronize_rcu();
- poll(NULL, 0, 100);
- synchronize_rcu();
pap->nlookups = nlookups;
pap->nlookupfails = nlookupfails;
@@ -1136,15 +1140,19 @@ void *zoo_updater(void *arg)
quiescent_state();
}
+ rcu_barrier();
/* Test over, so remove all our elements from the hash table. */
for (i = 0; i < elperupdater; i++) {
if (!zheplist[i])
continue;
zoo_del(zheplist[i]);
}
+ rcu_barrier();
+
hash_unregister_thread();
pap->nadds = nadds;
pap->ndels = ndels;
+ free(zheplist);
return NULL;
}
--
2.7.4
