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    SubjectRe: [PATCH 9/9] Kprobes: Use RCU for (un)register synchronization - arch changes
    On Mon, Oct 10, 2005 at 10:48:13AM -0400, Ananth N Mavinakayanahalli wrote:
    > From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    >
    > 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.

    And a few very similar questions here as well...

    Thanx, Paul

    > Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    > Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
    > ---
    >
    > arch/i386/kernel/kprobes.c | 22 +++++++---------------
    > arch/ia64/kernel/kprobes.c | 16 ++++++----------
    > arch/ppc64/kernel/kprobes.c | 24 ++++++------------------
    > arch/sparc64/kernel/kprobes.c | 14 ++------------
    > arch/x86_64/kernel/kprobes.c | 25 ++++++-------------------
    > 5 files changed, 27 insertions(+), 74 deletions(-)
    >
    > Index: linux-2.6.14-rc3/arch/i386/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.14-rc3.orig/arch/i386/kernel/kprobes.c 2005-10-05 16:08:13.000000000 -0400
    > +++ linux-2.6.14-rc3/arch/i386/kernel/kprobes.c 2005-10-05 16:08:48.000000000 -0400
    > @@ -31,7 +31,6 @@
    > #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>
    > @@ -123,6 +122,7 @@ static inline void prepare_singlestep(st
    > regs->eip = (unsigned long)&p->ainsn.insn;
    > }
    >
    > +/* Called with kretprobe_lock held */
    > void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
    > struct pt_regs *regs)
    > {
    > @@ -168,15 +168,12 @@ static int __kprobes kprobe_handler(stru
    > }
    > /* 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) {
    > if (kcb->kprobe_status == KPROBE_HIT_SS &&
    > *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
    > regs->eflags &= ~TF_MASK;
    > regs->eflags |= kcb->kprobe_saved_eflags;
    > - unlock_kprobes();
    > goto no_kprobe;
    > }
    > /* We have reentered the kprobe_handler(), since
    > @@ -197,14 +194,11 @@ static int __kprobes kprobe_handler(stru
    > 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 (regs->eflags & VM_MASK) {
    > /* We are in virtual-8086 mode. Return 0 */
    > goto no_kprobe;
    > @@ -268,9 +262,10 @@ int __kprobes trampoline_probe_handler(s
    > 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);
    >
    > /*
    > @@ -310,7 +305,7 @@ int __kprobes trampoline_probe_handler(s
    > regs->eip = orig_ret_address;
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > + spin_unlock_irqrestore(&kretprobe_lock, flags);
    > preempt_enable_no_resched();
    >
    > /*
    > @@ -395,7 +390,7 @@ static void __kprobes resume_execution(s
    >
    > /*
    > * Interrupts are disabled on entry as trap1 is an interrupt gate and they
    > - * remain disabled thoroughout this function. And we hold kprobe lock.
    > + * remain disabled thoroughout this function.
    > */
    > static inline int post_kprobe_handler(struct pt_regs *regs)
    > {
    > @@ -419,7 +414,6 @@ static inline int post_kprobe_handler(st
    > goto out;
    > }
    > reset_current_kprobe();
    > - unlock_kprobes();
    > out:
    > preempt_enable_no_resched();
    >
    > @@ -434,7 +428,6 @@ 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();
    > @@ -448,7 +441,6 @@ static inline int kprobe_fault_handler(s
    > regs->eflags |= kcb->kprobe_old_eflags;
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > preempt_enable_no_resched();
    > }
    > return 0;
    > @@ -463,7 +455,7 @@ int __kprobes kprobe_exceptions_notify(s
    > struct die_args *args = (struct die_args *)data;
    > int ret = NOTIFY_DONE;
    >
    > - preempt_disable();
    > + rcu_read_lock();

    If synchronize_sched() is used on the update side, this needs to
    remain preempt_disable() rather than rcu_read_lock().

    > switch (val) {
    > case DIE_INT3:
    > if (kprobe_handler(args->regs))
    > @@ -482,7 +474,7 @@ int __kprobes kprobe_exceptions_notify(s
    > default:
    > break;
    > }
    > - preempt_enable();
    > + rcu_read_unlock();
    > return ret;
    > }
    >
    > Index: linux-2.6.14-rc3/arch/ia64/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.14-rc3.orig/arch/ia64/kernel/kprobes.c 2005-10-05 16:08:14.000000000 -0400
    > +++ linux-2.6.14-rc3/arch/ia64/kernel/kprobes.c 2005-10-05 16:08:48.000000000 -0400
    > @@ -26,7 +26,6 @@
    > #include <linux/config.h>
    > #include <linux/kprobes.h>
    > #include <linux/ptrace.h>
    > -#include <linux/spinlock.h>
    > #include <linux/string.h>
    > #include <linux/slab.h>
    > #include <linux/preempt.h>
    > @@ -343,10 +342,11 @@ int __kprobes trampoline_probe_handler(s
    > 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 =
    > ((struct fnptr *)kretprobe_trampoline)->ip;
    >
    > + spin_lock_irqsave(&kretprobe_lock, flags);
    > head = kretprobe_inst_table_head(current);
    >
    > /*
    > @@ -386,7 +386,7 @@ int __kprobes trampoline_probe_handler(s
    > regs->cr_iip = orig_ret_address;
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > + spin_unlock_irqrestore(&kretprobe_lock, flags);
    > preempt_enable_no_resched();
    >
    > /*
    > @@ -397,6 +397,7 @@ int __kprobes trampoline_probe_handler(s
    > return 1;
    > }
    >
    > +/* Called with kretprobe_lock held */
    > void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
    > struct pt_regs *regs)
    > {
    > @@ -612,7 +613,6 @@ static int __kprobes pre_kprobes_handler
    > if ((kcb->kprobe_status == KPROBE_HIT_SS) &&
    > (p->ainsn.inst_flag == INST_FLAG_BREAK_INST)) {
    > ia64_psr(regs)->ss = 0;
    > - unlock_kprobes();
    > goto no_kprobe;
    > }
    > /* We have reentered the pre_kprobe_handler(), since
    > @@ -641,10 +641,8 @@ static int __kprobes pre_kprobes_handler
    > }
    > }
    >
    > - lock_kprobes();
    > p = get_kprobe(addr);
    > if (!p) {
    > - unlock_kprobes();
    > if (!is_ia64_break_inst(regs)) {
    > /*
    > * The breakpoint instruction was removed right
    > @@ -707,7 +705,6 @@ static int __kprobes post_kprobes_handle
    > goto out;
    > }
    > reset_current_kprobe();
    > - unlock_kprobes();
    >
    > out:
    > preempt_enable_no_resched();
    > @@ -728,7 +725,6 @@ static int __kprobes kprobes_fault_handl
    > if (kcb->kprobe_status & KPROBE_HIT_SS) {
    > resume_execution(cur, regs);
    > reset_current_kprobe();
    > - unlock_kprobes();
    > preempt_enable_no_resched();
    > }
    >
    > @@ -741,7 +737,7 @@ int __kprobes kprobe_exceptions_notify(s
    > struct die_args *args = (struct die_args *)data;
    > int ret = NOTIFY_DONE;
    >
    > - preempt_disable();
    > + rcu_read_lock();

    Ditto here...

    > switch(val) {
    > case DIE_BREAK:
    > if (pre_kprobes_handler(args))
    > @@ -757,7 +753,7 @@ int __kprobes kprobe_exceptions_notify(s
    > default:
    > break;
    > }
    > - preempt_enable();
    > + rcu_read_unlock();
    > return ret;
    > }
    >
    > Index: linux-2.6.14-rc3/arch/ppc64/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.14-rc3.orig/arch/ppc64/kernel/kprobes.c 2005-10-05 16:08:15.000000000 -0400
    > +++ linux-2.6.14-rc3/arch/ppc64/kernel/kprobes.c 2005-10-05 16:08:48.000000000 -0400
    > @@ -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(st
    > 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
    >
    > /* 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
    > 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
    > 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(s
    > 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(s
    > 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(st
    > 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(s
    > 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(s
    > 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();

    And here...

    > switch (val) {
    > case DIE_BPT:
    > if (kprobe_handler(args->regs))
    > @@ -416,7 +404,7 @@ int __kprobes kprobe_exceptions_notify(s
    > default:
    > break;
    > }
    > - preempt_enable_no_resched();
    > + rcu_read_unlock();
    > return ret;
    > }
    >
    > Index: linux-2.6.14-rc3/arch/sparc64/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.14-rc3.orig/arch/sparc64/kernel/kprobes.c 2005-10-05 16:08:15.000000000 -0400
    > +++ linux-2.6.14-rc3/arch/sparc64/kernel/kprobes.c 2005-10-05 16:08:48.000000000 -0400
    > @@ -116,15 +116,11 @@ static int __kprobes kprobe_handler(stru
    > struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    >
    > 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) {
    > if (kcb->kprobe_status == KPROBE_HIT_SS) {
    > regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
    > kcb->kprobe_orig_tstate_pil);
    > - unlock_kprobes();
    > goto no_kprobe;
    > }
    > /* We have reentered the kprobe_handler(), since
    > @@ -144,14 +140,11 @@ static int __kprobes kprobe_handler(stru
    > if (p->break_handler && p->break_handler(p, 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 (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
    > /*
    > * The breakpoint instruction was removed right
    > @@ -296,14 +289,12 @@ static inline int post_kprobe_handler(st
    > goto out;
    > }
    > reset_current_kprobe();
    > - unlock_kprobes();
    > out:
    > preempt_enable_no_resched();
    >
    > return 1;
    > }
    >
    > -/* Interrupts disabled, kprobe_lock held. */
    > static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
    > {
    > struct kprobe *cur = kprobe_running();
    > @@ -316,7 +307,6 @@ static inline int kprobe_fault_handler(s
    > resume_execution(cur, regs, kcb);
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > preempt_enable_no_resched();
    > }
    > return 0;
    > @@ -331,7 +321,7 @@ int __kprobes kprobe_exceptions_notify(s
    > struct die_args *args = (struct die_args *)data;
    > int ret = NOTIFY_DONE;
    >
    > - preempt_disable();
    > + rcu_read_lock();

    As well as here...

    > switch (val) {
    > case DIE_DEBUG:
    > if (kprobe_handler(args->regs))
    > @@ -350,7 +340,7 @@ int __kprobes kprobe_exceptions_notify(s
    > default:
    > break;
    > }
    > - preempt_enable();
    > + rcu_read_unlock();
    > return ret;
    > }
    >
    > Index: linux-2.6.14-rc3/arch/x86_64/kernel/kprobes.c
    > ===================================================================
    > --- linux-2.6.14-rc3.orig/arch/x86_64/kernel/kprobes.c 2005-10-05 16:08:33.000000000 -0400
    > +++ linux-2.6.14-rc3/arch/x86_64/kernel/kprobes.c 2005-10-05 16:08:48.000000000 -0400
    > @@ -34,7 +34,6 @@
    > #include <linux/config.h>
    > #include <linux/kprobes.h>
    > #include <linux/ptrace.h>
    > -#include <linux/spinlock.h>
    > #include <linux/string.h>
    > #include <linux/slab.h>
    > #include <linux/preempt.h>
    > @@ -266,6 +265,7 @@ static void __kprobes prepare_singlestep
    > regs->rip = (unsigned long)p->ainsn.insn;
    > }
    >
    > +/* Called with kretprobe_lock held */
    > void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
    > struct pt_regs *regs)
    > {
    > @@ -299,15 +299,12 @@ int __kprobes kprobe_handler(struct pt_r
    >
    > /* 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) {
    > if (kcb->kprobe_status == KPROBE_HIT_SS &&
    > *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
    > regs->eflags &= ~TF_MASK;
    > regs->eflags |= kcb->kprobe_saved_rflags;
    > - unlock_kprobes();
    > goto no_kprobe;
    > } else if (kcb->kprobe_status == KPROBE_HIT_SSDONE) {
    > /* TODO: Provide re-entrancy from
    > @@ -340,14 +337,11 @@ int __kprobes kprobe_handler(struct pt_r
    > 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) {
    > /*
    > * The breakpoint instruction was removed right
    > @@ -406,9 +400,10 @@ int __kprobes trampoline_probe_handler(s
    > 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);
    >
    > /*
    > @@ -448,7 +443,7 @@ int __kprobes trampoline_probe_handler(s
    > regs->rip = orig_ret_address;
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > + spin_unlock_irqrestore(&kretprobe_lock, flags);
    > preempt_enable_no_resched();
    >
    > /*
    > @@ -536,10 +531,6 @@ static void __kprobes resume_execution(s
    > }
    > }
    >
    > -/*
    > - * Interrupts are disabled on entry as trap1 is an interrupt gate and they
    > - * remain disabled thoroughout this function. And we hold kprobe lock.
    > - */
    > int __kprobes post_kprobe_handler(struct pt_regs *regs)
    > {
    > struct kprobe *cur = kprobe_running();
    > @@ -560,8 +551,6 @@ int __kprobes post_kprobe_handler(struct
    > if (kcb->kprobe_status == KPROBE_REENTER) {
    > restore_previous_kprobe(kcb);
    > goto out;
    > - } else {
    > - unlock_kprobes();
    > }
    > reset_current_kprobe();
    > out:
    > @@ -578,7 +567,6 @@ out:
    > return 1;
    > }
    >
    > -/* Interrupts disabled, kprobe_lock held. */
    > int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
    > {
    > struct kprobe *cur = kprobe_running();
    > @@ -592,7 +580,6 @@ int __kprobes kprobe_fault_handler(struc
    > regs->eflags |= kcb->kprobe_old_rflags;
    >
    > reset_current_kprobe();
    > - unlock_kprobes();
    > preempt_enable_no_resched();
    > }
    > return 0;
    > @@ -607,7 +594,7 @@ int __kprobes kprobe_exceptions_notify(s
    > struct die_args *args = (struct die_args *)data;
    > int ret = NOTIFY_DONE;
    >
    > - preempt_disable();
    > + rcu_read_lock();

    As well as here yet again...

    > switch (val) {
    > case DIE_INT3:
    > if (kprobe_handler(args->regs))
    > @@ -626,7 +613,7 @@ int __kprobes kprobe_exceptions_notify(s
    > default:
    > break;
    > }
    > - preempt_enable();
    > + rcu_read_unlock();
    > return ret;
    > }
    >
    > -
    > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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