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>hifive-unleashed-5.1
parent
f0f2c2b5b4
commit
fb842b00c5
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@ -39,6 +39,7 @@
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#include <linux/syslog.h>
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#include <linux/syslog.h>
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#include <linux/cpu.h>
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#include <linux/cpu.h>
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#include <linux/notifier.h>
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#include <linux/notifier.h>
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#include <linux/rculist.h>
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#include <asm/uaccess.h>
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#include <asm/uaccess.h>
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@ -1502,7 +1503,7 @@ int kmsg_dump_register(struct kmsg_dumper *dumper)
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/* Don't allow registering multiple times */
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/* Don't allow registering multiple times */
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if (!dumper->registered) {
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if (!dumper->registered) {
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dumper->registered = 1;
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dumper->registered = 1;
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list_add_tail(&dumper->list, &dump_list);
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list_add_tail_rcu(&dumper->list, &dump_list);
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err = 0;
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err = 0;
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}
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}
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spin_unlock_irqrestore(&dump_list_lock, flags);
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spin_unlock_irqrestore(&dump_list_lock, flags);
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@ -1526,33 +1527,16 @@ int kmsg_dump_unregister(struct kmsg_dumper *dumper)
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spin_lock_irqsave(&dump_list_lock, flags);
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spin_lock_irqsave(&dump_list_lock, flags);
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if (dumper->registered) {
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if (dumper->registered) {
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dumper->registered = 0;
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dumper->registered = 0;
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list_del(&dumper->list);
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list_del_rcu(&dumper->list);
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err = 0;
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err = 0;
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}
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}
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spin_unlock_irqrestore(&dump_list_lock, flags);
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spin_unlock_irqrestore(&dump_list_lock, flags);
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synchronize_rcu();
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return err;
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return err;
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}
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}
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EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
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EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
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static const char * const kmsg_reasons[] = {
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[KMSG_DUMP_OOPS] = "oops",
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[KMSG_DUMP_PANIC] = "panic",
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[KMSG_DUMP_KEXEC] = "kexec",
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[KMSG_DUMP_RESTART] = "restart",
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[KMSG_DUMP_HALT] = "halt",
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[KMSG_DUMP_POWEROFF] = "poweroff",
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[KMSG_DUMP_EMERG] = "emergency_restart",
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};
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static const char *kmsg_to_str(enum kmsg_dump_reason reason)
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{
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if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
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return "unknown";
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return kmsg_reasons[reason];
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}
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/**
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/**
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* kmsg_dump - dump kernel log to kernel message dumpers.
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* kmsg_dump - dump kernel log to kernel message dumpers.
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* @reason: the reason (oops, panic etc) for dumping
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* @reason: the reason (oops, panic etc) for dumping
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@ -1591,13 +1575,9 @@ void kmsg_dump(enum kmsg_dump_reason reason)
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l2 = chars;
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l2 = chars;
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}
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}
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if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
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rcu_read_lock();
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printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
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list_for_each_entry_rcu(dumper, &dump_list, list)
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kmsg_to_str(reason));
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return;
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}
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list_for_each_entry(dumper, &dump_list, list)
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dumper->dump(dumper, reason, s1, l1, s2, l2);
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dumper->dump(dumper, reason, s1, l1, s2, l2);
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spin_unlock_irqrestore(&dump_list_lock, flags);
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rcu_read_unlock();
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}
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}
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#endif
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#endif
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