The patch titled
printk: use RCU to prevent potential lock contention in kmsg_dump
has been added to the -mm tree. Its filename is
printk-use-rcu-to-prevent-potential-lock-contention-in-kmsg_dump.patch
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The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: printk: use RCU to prevent potential lock contention in kmsg_dump
From: Huang Ying <ying.huang@xxxxxxxxx>
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@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk.c | 30 +++++++-----------------------
1 file changed, 7 insertions(+), 23 deletions(-)
diff -puN kernel/printk.c~printk-use-rcu-to-prevent-potential-lock-contention-in-kmsg_dump kernel/printk.c
--- a/kernel/printk.c~printk-use-rcu-to-prevent-potential-lock-contention-in-kmsg_dump
+++ a/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>
@@ -1498,7 +1499,7 @@ int kmsg_dump_register(struct kmsg_dumpe
/* 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);
@@ -1522,29 +1523,16 @@ int kmsg_dump_unregister(struct kmsg_dum
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",
-};
-
-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
@@ -1583,13 +1571,9 @@ void kmsg_dump(enum kmsg_dump_reason rea
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
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
linux-next.patch
printk-use-rcu-to-prevent-potential-lock-contention-in-kmsg_dump.patch
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