On Mon, Oct 17, 2005 at 10:49:30PM -0700, Paul E. McKenney wrote:
> On Mon, Oct 10, 2005 at 10:48:13AM -0400, Ananth N Mavinakayanahalli wrote:
> > From: Ananth N Mavinakayanahalli <[email protected]>
> >
> > 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...
Replies inline...
Ananth
> Thanx, Paul
>
> > Signed-off-by: Ananth N Mavinakayanahalli <[email protected]>
> > Signed-off-by: Anil S Keshavamurthy <[email protected]>
> > ---
> >
> > 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().
Kprobe handlers can't block/sleep. So the idea is to depend on a
schedule() event to ensure handlers have executed. This and the others
you have pointed out can surely be preempt_disable().
> > 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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> >
> >
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