[lxc-devel] [PATCH] remove static_lock()/static_unlock() and start to use thread local storage (v2)
S.Çağlar Onur
caglar at 10ur.org
Thu Dec 19 05:08:51 UTC 2013
While testing https://github.com/lxc/lxc/pull/106, I found that concurrent starts
are hanging time to time. I then reproduced the same problem in master and got following;
[caglar at oOo:~] sudo gdb -p 16221
(gdb) bt
#0 __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 0x00007f495526515c in _L_lock_982 () from /lib/x86_64-linux-gnu/libpthread.so.0
#2 0x00007f4955264fab in __GI___pthread_mutex_lock (mutex=0x7f49556d4600 <static_mutex>) at pthread_mutex_lock.c:64
#3 0x00007f49554b27a6 in lock_mutex (l=l at entry=0x7f49556d4600 <static_mutex>) at lxclock.c:78
#4 0x00007f49554b2dac in static_lock () at lxclock.c:330
#5 0x00007f4955498f71 in lxc_global_config_value (option_name=option_name at entry=0x7f49554c02cf "cgroup.use") at utils.c:273
#6 0x00007f495549926c in default_cgroup_use () at utils.c:366
#7 0x00007f49554953bd in lxc_cgroup_load_meta () at cgroup.c:94
#8 0x00007f495548debc in lxc_spawn (handler=handler at entry=0x7f49200af300) at start.c:783
#9 0x00007f495548e7a7 in __lxc_start (name=name at entry=0x7f49200b48a0 "lxc-test-concurrent-4", conf=conf at entry=0x7f49200b2030, ops=ops at entry=0x7f49556d3900 <start_ops>, data=data at entry=0x7f495487db90,
lxcpath=lxcpath at entry=0x7f49200b2010 "/var/lib/lxc") at start.c:951
#10 0x00007f495548eb9c in lxc_start (name=0x7f49200b48a0 "lxc-test-concurrent-4", argv=argv at entry=0x7f495487dbe0, conf=conf at entry=0x7f49200b2030, lxcpath=0x7f49200b2010 "/var/lib/lxc") at start.c:1048
#11 0x00007f49554b68f1 in lxcapi_start (c=0x7f49200b1dd0, useinit=<optimized out>, argv=0x7f495487dbe0) at lxccontainer.c:648
#12 0x0000000000401317 in do_function (arguments=0x1aa80b0) at concurrent.c:94
#13 0x0000000000401499 in concurrent (arguments=<optimized out>) at concurrent.c:130
#14 0x00007f4955262f6e in start_thread (arg=0x7f495487e700) at pthread_create.c:311
#15 0x00007f4954f8d9cd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113
It looks like both parent and child end up with locked mutex thus deadlocks.
I ended up placing values in the thread local storage pool, instead of doing "unlock the lock in the child" dance
Signed-off-by: S.Çağlar Onur <caglar at 10ur.org>
---
src/lxc/lxclock.c | 13 -------------
src/lxc/lxclock.h | 10 ----------
src/lxc/utils.c | 16 +++-------------
3 files changed, 3 insertions(+), 36 deletions(-)
diff --git a/src/lxc/lxclock.c b/src/lxc/lxclock.c
index 64823d2..62e774f 100644
--- a/src/lxc/lxclock.c
+++ b/src/lxc/lxclock.c
@@ -44,7 +44,6 @@ lxc_log_define(lxc_lock, lxc);
#ifdef MUTEX_DEBUGGING
pthread_mutex_t thread_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
-pthread_mutex_t static_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
inline void dump_stacktrace(void)
{
@@ -66,7 +65,6 @@ inline void dump_stacktrace(void)
}
#else
pthread_mutex_t thread_mutex = PTHREAD_MUTEX_INITIALIZER;
-pthread_mutex_t static_mutex = PTHREAD_MUTEX_INITIALIZER;
inline void dump_stacktrace(void) {;}
#endif
@@ -324,17 +322,6 @@ void process_unlock(void)
unlock_mutex(&thread_mutex);
}
-/* Protects static const values inside the lxc_global_config_value funtion */
-void static_lock(void)
-{
- lock_mutex(&static_mutex);
-}
-
-void static_unlock(void)
-{
- unlock_mutex(&static_mutex);
-}
-
int container_mem_lock(struct lxc_container *c)
{
return lxclock(c->privlock, 0);
diff --git a/src/lxc/lxclock.h b/src/lxc/lxclock.h
index 820e819..a02a032 100644
--- a/src/lxc/lxclock.h
+++ b/src/lxc/lxclock.h
@@ -123,16 +123,6 @@ extern void process_lock(void);
*/
extern void process_unlock(void);
-/*!
- * \brief Lock global data.
- */
-extern void static_lock(void);
-
-/*!
- * \brief Unlock global data.
- */
-extern void static_unlock(void);
-
struct lxc_container;
/*!
diff --git a/src/lxc/utils.c b/src/lxc/utils.c
index b605307..785f3e6 100644
--- a/src/lxc/utils.c
+++ b/src/lxc/utils.c
@@ -253,8 +253,8 @@ const char *lxc_global_config_value(const char *option_name)
{ "cgroup.use", NULL },
{ NULL, NULL },
};
- /* Protected by a mutex to eliminate conflicting load and store operations */
- static const char *values[sizeof(options) / sizeof(options[0])] = { 0 };
+ /* placed in the thread local storage pool */
+ static __thread const char *values[sizeof(options) / sizeof(options[0])] = { 0 };
const char *(*ptr)[2];
const char *value;
size_t i;
@@ -270,13 +270,10 @@ const char *lxc_global_config_value(const char *option_name)
return NULL;
}
- static_lock();
if (values[i]) {
value = values[i];
- static_unlock();
return value;
}
- static_unlock();
process_lock();
fin = fopen_cloexec(LXC_GLOBAL_CONF, "r");
@@ -313,21 +310,17 @@ const char *lxc_global_config_value(const char *option_name)
while (*p && (*p == ' ' || *p == '\t')) p++;
if (!*p)
continue;
- static_lock();
values[i] = copy_global_config_value(p);
- static_unlock();
goto out;
}
}
/* could not find value, use default */
- static_lock();
values[i] = (*ptr)[1];
/* special case: if default value is NULL,
* and there is no config, don't view that
* as an error... */
if (!values[i])
errno = 0;
- static_unlock();
out:
process_lock();
@@ -335,10 +328,7 @@ out:
fclose(fin);
process_unlock();
- static_lock();
- value = values[i];
- static_unlock();
- return value;
+ return values[i];
}
const char *default_lvm_vg(void)
--
1.8.3.2
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