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authorHuang Ying <ying.huang@intel.com>2011-01-12 16:59:43 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 08:03:09 -0800
commitfb842b00c5eab66ec361b31550aa8a922745ce9e (patch)
treecef7e6a0bd01849fcfc911f36293304f9ba7b3c2 /kernel
parentf0f2c2b5b40b5e621a47a6a274117cce77841f1e (diff)
downloadlinux-linaro-precise-fb842b00c5eab66ec361b31550aa8a922745ce9e.tar.gz
printk: use RCU to prevent potential lock contention in kmsg_dump
dump_list_lock is used to protect dump_list in kmsg_dumper implementation, kmsg_dump() uses it to traverse dump_list too. But if there is contention on the lock, kmsg_dump() will fail, and the valuable kernel message may be lost. This patch solves this issue with RCU. Because kmsg_dump() only read the list, no lock is needed in kmsg_dump(). So that kmsg_dump() will never fail because of lock contention. Signed-off-by: Huang Ying <ying.huang@intel.com> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk.c34
1 files changed, 7 insertions, 27 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index 0b0c9aa71e8..53d9a9ec88e 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -39,6 +39,7 @@
#include <linux/syslog.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
+#include <linux/rculist.h>
#include <asm/uaccess.h>
@@ -1502,7 +1503,7 @@ int kmsg_dump_register(struct kmsg_dumper *dumper)
/* Don't allow registering multiple times */
if (!dumper->registered) {
dumper->registered = 1;
- list_add_tail(&dumper->list, &dump_list);
+ list_add_tail_rcu(&dumper->list, &dump_list);
err = 0;
}
spin_unlock_irqrestore(&dump_list_lock, flags);
@@ -1526,33 +1527,16 @@ int kmsg_dump_unregister(struct kmsg_dumper *dumper)
spin_lock_irqsave(&dump_list_lock, flags);
if (dumper->registered) {
dumper->registered = 0;
- list_del(&dumper->list);
+ list_del_rcu(&dumper->list);
err = 0;
}
spin_unlock_irqrestore(&dump_list_lock, flags);
+ synchronize_rcu();
return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
-static const char * const kmsg_reasons[] = {
- [KMSG_DUMP_OOPS] = "oops",
- [KMSG_DUMP_PANIC] = "panic",
- [KMSG_DUMP_KEXEC] = "kexec",
- [KMSG_DUMP_RESTART] = "restart",
- [KMSG_DUMP_HALT] = "halt",
- [KMSG_DUMP_POWEROFF] = "poweroff",
- [KMSG_DUMP_EMERG] = "emergency_restart",
-};
-
-static const char *kmsg_to_str(enum kmsg_dump_reason reason)
-{
- if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
- return "unknown";
-
- return kmsg_reasons[reason];
-}
-
/**
* kmsg_dump - dump kernel log to kernel message dumpers.
* @reason: the reason (oops, panic etc) for dumping
@@ -1591,13 +1575,9 @@ void kmsg_dump(enum kmsg_dump_reason reason)
l2 = chars;
}
- if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
- printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
- kmsg_to_str(reason));
- return;
- }
- list_for_each_entry(dumper, &dump_list, list)
+ rcu_read_lock();
+ list_for_each_entry_rcu(dumper, &dump_list, list)
dumper->dump(dumper, reason, s1, l1, s2, l2);
- spin_unlock_irqrestore(&dump_list_lock, flags);
+ rcu_read_unlock();
}
#endif