[PATCH] Kprobes: Use RCU for (un)register synchronization - arch changes

Changes to the arch kprobes infrastructure to take advantage of the locking
changes introduced by usage of RCU for synchronization.  All handlers are now
run without any locks held, so they have to be re-entrant or provide their own
synchronization.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 18 deletions

diff --git a/arch/ppc64/kernel/kprobes.c b/arch/ppc64/kernel/kprobes.c
index 3f89f3e5584a..e0a25b35437f 100644
--- a/arch/ppc64/kernel/kprobes.c
+++ b/arch/ppc64/kernel/kprobes.c
@@ -30,7 +30,6 @@
 #include <linux/config.h>
 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
-#include <linux/spinlock.h>
 #include <linux/preempt.h>
 #include <asm/cacheflush.h>
 #include <asm/kdebug.h>
@@ -125,6 +124,7 @@ static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
         kcb->kprobe_saved_msr = regs->msr;
 }
 
+/* Called with kretprobe_lock held */
 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
                                       struct pt_regs *regs)
 {
@@ -152,8 +152,6 @@ static inline int kprobe_handler(struct pt_regs *regs)
 
         /* Check we're not actually recursing */
         if (kprobe_running()) {
-                /* We *are* holding lock here, so this is safe.
-                   Disarm the probe we just hit, and ignore it. */
                 p = get_kprobe(addr);
                 if (p) {
                         kprobe_opcode_t insn = *p->ainsn.insn;
@@ -161,7 +159,6 @@ static inline int kprobe_handler(struct pt_regs *regs)
                                         is_trap(insn)) {
                                 regs->msr &= ~MSR_SE;
                                 regs->msr |= kcb->kprobe_saved_msr;
-                                unlock_kprobes();
                                 goto no_kprobe;
                         }
                         /* We have reentered the kprobe_handler(), since
@@ -183,14 +180,11 @@ static inline int kprobe_handler(struct pt_regs *regs)
                                 goto ss_probe;
                         }
                 }
-                /* If it's not ours, can't be delete race, (we hold lock). */
                 goto no_kprobe;
         }
 
-        lock_kprobes();
         p = get_kprobe(addr);
         if (!p) {
-                unlock_kprobes();
                 if (*addr != BREAKPOINT_INSTRUCTION) {
                         /*
                          * PowerPC has multiple variants of the "trap"
@@ -254,9 +248,10 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
         struct kretprobe_instance *ri = NULL;
         struct hlist_head *head;
         struct hlist_node *node, *tmp;
-        unsigned long orig_ret_address = 0;
+        unsigned long flags, orig_ret_address = 0;
         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 
+        spin_lock_irqsave(&kretprobe_lock, flags);
         head = kretprobe_inst_table_head(current);
 
         /*
@@ -296,7 +291,7 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
         regs->nip = orig_ret_address;
 
         reset_current_kprobe();
-        unlock_kprobes();
+        spin_unlock_irqrestore(&kretprobe_lock, flags);
         preempt_enable_no_resched();
 
         /*
@@ -348,7 +343,6 @@ static inline int post_kprobe_handler(struct pt_regs *regs)
                 goto out;
         }
         reset_current_kprobe();
-        unlock_kprobes();
 out:
         preempt_enable_no_resched();
 
@@ -363,7 +357,6 @@ out:
         return 1;
 }
 
-/* Interrupts disabled, kprobe_lock held. */
 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
         struct kprobe *cur = kprobe_running();
@@ -378,7 +371,6 @@ static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                 regs->msr |= kcb->kprobe_saved_msr;
 
                 reset_current_kprobe();
-                unlock_kprobes();
                 preempt_enable_no_resched();
         }
         return 0;
@@ -393,11 +385,7 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
         struct die_args *args = (struct die_args *)data;
         int ret = NOTIFY_DONE;
 
-        /*
-         * Interrupts are not disabled here.  We need to disable
-         * preemption, because kprobe_running() uses smp_processor_id().
-         */
-        preempt_disable();
+        rcu_read_lock();
         switch (val) {
         case DIE_BPT:
                 if (kprobe_handler(args->regs))
@@ -415,7 +403,7 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
         default:
                 break;
         }
-        preempt_enable_no_resched();
+        rcu_read_unlock();
         return ret;
 }