Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
On 07/24, Ravi Bangoria wrote: > > > Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by > > delayed_uprobe_add(). > > Yes, good idea. But let me repeat, lets do this later. We can do even better I think, say, move this delaed-list into uprobes_state. But imo the 1st version can just check MMF_HAS_UPROBES because this is simple, obviously correct, and can actually help. Oleg.
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
On 07/24, Ravi Bangoria wrote: > > > Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by > > delayed_uprobe_add(). > > Yes, good idea. But let me repeat, lets do this later. We can do even better I think, say, move this delaed-list into uprobes_state. But imo the 1st version can just check MMF_HAS_UPROBES because this is simple, obviously correct, and can actually help. Oleg.
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Hi Ravi,
Thank you for updating the series. At least trace_uprobe side,
it looks good to me ;)
Reviewed-by: Masami Hiramatsu
Thanks!
On Mon, 16 Jul 2018 14:17:03 +0530
Ravi Bangoria wrote:
> Userspace Statically Defined Tracepoints[1] are dtrace style markers
> inside userspace applications. Applications like PostgreSQL, MySQL,
> Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc
> have these markers embedded in them. These markers are added by developer
> at important places in the code. Each marker source expands to a single
> nop instruction in the compiled code but there may be additional
> overhead for computing the marker arguments which expands to couple of
> instructions. In case the overhead is more, execution of it can be
> omitted by runtime if() condition when no one is tracing on the marker:
>
> if (reference_counter > 0) {
> Execute marker instructions;
> }
>
> Default value of reference counter is 0. Tracer has to increment the
> reference counter before tracing on a marker and decrement it when
> done with the tracing.
>
> Implement the reference counter logic in core uprobe. User will be
> able to use it from trace_uprobe as well as from kernel module. New
> trace_uprobe definition with reference counter will now be:
>
> :[(ref_ctr_offset)]
>
> where ref_ctr_offset is an optional field. For kernel module, new
> variant of uprobe_register() has been introduced:
>
> uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer)
>
> No new variant for uprobe_unregister() because it's assumed to have
> only one reference counter for one uprobe.
>
> [1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
>
> Note: 'reference counter' is called as 'semaphore' in original Dtrace
> (or Systemtap, bcc and even in ELF) documentation and code. But the
> term 'semaphore' is misleading in this context. This is just a counter
> used to hold number of tracers tracing on a marker. This is not really
> used for any synchronization. So we are referring it as 'reference
> counter' in kernel / perf code.
>
> Signed-off-by: Ravi Bangoria
> ---
> include/linux/uprobes.h | 5 +
> kernel/events/uprobes.c | 232
> ++--
> kernel/trace/trace.c| 2 +-
> kernel/trace/trace_uprobe.c | 38 +++-
> 4 files changed, 267 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index bb9d2084af03..103a48a48872 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -123,6 +123,7 @@ extern unsigned long uprobe_get_swbp_addr(struct pt_regs
> *regs);
> extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct
> *mm, unsigned long vaddr, uprobe_opcode_t);
> extern int uprobe_register(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc);
> +extern int uprobe_register_refctr(struct inode *inode, loff_t offset, loff_t
> ref_ctr_offset, struct uprobe_consumer *uc);
> extern int uprobe_apply(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc, bool);
> extern void uprobe_unregister(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc);
> extern int uprobe_mmap(struct vm_area_struct *vma);
> @@ -160,6 +161,10 @@ uprobe_register(struct inode *inode, loff_t offset,
> struct uprobe_consumer *uc)
> {
> return -ENOSYS;
> }
> +static inline int uprobe_register_refctr(struct inode *inode, loff_t offset,
> loff_t ref_ctr_offset, struct uprobe_consumer *uc)
> +{
> + return -ENOSYS;
> +}
> static inline int
> uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc,
> bool add)
> {
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index c0418ba52ba8..84da8512a974 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -73,6 +73,7 @@ struct uprobe {
> struct uprobe_consumer *consumers;
> struct inode*inode; /* Also hold a ref to inode */
> loff_t offset;
> + loff_t ref_ctr_offset;
> unsigned long flags;
>
> /*
> @@ -88,6 +89,15 @@ struct uprobe {
> struct arch_uprobe arch;
> };
>
> +struct delayed_uprobe {
> + struct list_head list;
> + struct uprobe *uprobe;
> + struct mm_struct *mm;
> +};
> +
> +static DEFINE_MUTEX(delayed_uprobe_lock);
> +static LIST_HEAD(delayed_uprobe_list);
> +
> /*
> * Execute out of line area: anonymous executable mapping installed
> * by the probed task to execute the copy of the original instruction
> @@ -282,6 +292,154 @@ static int verify_opcode(struct page *page, unsigned
> long vaddr, uprobe_opcode_t
> return 1;
> }
>
> +static struct delayed_uprobe *
> +delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
> +{
> + struct delayed_uprobe *du;
> +
> +
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Hi Ravi,
Thank you for updating the series. At least trace_uprobe side,
it looks good to me ;)
Reviewed-by: Masami Hiramatsu
Thanks!
On Mon, 16 Jul 2018 14:17:03 +0530
Ravi Bangoria wrote:
> Userspace Statically Defined Tracepoints[1] are dtrace style markers
> inside userspace applications. Applications like PostgreSQL, MySQL,
> Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc
> have these markers embedded in them. These markers are added by developer
> at important places in the code. Each marker source expands to a single
> nop instruction in the compiled code but there may be additional
> overhead for computing the marker arguments which expands to couple of
> instructions. In case the overhead is more, execution of it can be
> omitted by runtime if() condition when no one is tracing on the marker:
>
> if (reference_counter > 0) {
> Execute marker instructions;
> }
>
> Default value of reference counter is 0. Tracer has to increment the
> reference counter before tracing on a marker and decrement it when
> done with the tracing.
>
> Implement the reference counter logic in core uprobe. User will be
> able to use it from trace_uprobe as well as from kernel module. New
> trace_uprobe definition with reference counter will now be:
>
> :[(ref_ctr_offset)]
>
> where ref_ctr_offset is an optional field. For kernel module, new
> variant of uprobe_register() has been introduced:
>
> uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer)
>
> No new variant for uprobe_unregister() because it's assumed to have
> only one reference counter for one uprobe.
>
> [1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
>
> Note: 'reference counter' is called as 'semaphore' in original Dtrace
> (or Systemtap, bcc and even in ELF) documentation and code. But the
> term 'semaphore' is misleading in this context. This is just a counter
> used to hold number of tracers tracing on a marker. This is not really
> used for any synchronization. So we are referring it as 'reference
> counter' in kernel / perf code.
>
> Signed-off-by: Ravi Bangoria
> ---
> include/linux/uprobes.h | 5 +
> kernel/events/uprobes.c | 232
> ++--
> kernel/trace/trace.c| 2 +-
> kernel/trace/trace_uprobe.c | 38 +++-
> 4 files changed, 267 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index bb9d2084af03..103a48a48872 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -123,6 +123,7 @@ extern unsigned long uprobe_get_swbp_addr(struct pt_regs
> *regs);
> extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct
> *mm, unsigned long vaddr, uprobe_opcode_t);
> extern int uprobe_register(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc);
> +extern int uprobe_register_refctr(struct inode *inode, loff_t offset, loff_t
> ref_ctr_offset, struct uprobe_consumer *uc);
> extern int uprobe_apply(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc, bool);
> extern void uprobe_unregister(struct inode *inode, loff_t offset, struct
> uprobe_consumer *uc);
> extern int uprobe_mmap(struct vm_area_struct *vma);
> @@ -160,6 +161,10 @@ uprobe_register(struct inode *inode, loff_t offset,
> struct uprobe_consumer *uc)
> {
> return -ENOSYS;
> }
> +static inline int uprobe_register_refctr(struct inode *inode, loff_t offset,
> loff_t ref_ctr_offset, struct uprobe_consumer *uc)
> +{
> + return -ENOSYS;
> +}
> static inline int
> uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc,
> bool add)
> {
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index c0418ba52ba8..84da8512a974 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -73,6 +73,7 @@ struct uprobe {
> struct uprobe_consumer *consumers;
> struct inode*inode; /* Also hold a ref to inode */
> loff_t offset;
> + loff_t ref_ctr_offset;
> unsigned long flags;
>
> /*
> @@ -88,6 +89,15 @@ struct uprobe {
> struct arch_uprobe arch;
> };
>
> +struct delayed_uprobe {
> + struct list_head list;
> + struct uprobe *uprobe;
> + struct mm_struct *mm;
> +};
> +
> +static DEFINE_MUTEX(delayed_uprobe_lock);
> +static LIST_HEAD(delayed_uprobe_list);
> +
> /*
> * Execute out of line area: anonymous executable mapping installed
> * by the probed task to execute the copy of the original instruction
> @@ -282,6 +292,154 @@ static int verify_opcode(struct page *page, unsigned
> long vaddr, uprobe_opcode_t
> return 1;
> }
>
> +static struct delayed_uprobe *
> +delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
> +{
> + struct delayed_uprobe *du;
> +
> +
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Hi Oleg,
On 07/23/2018 09:56 PM, Oleg Nesterov wrote:
> I have a mixed feeling about this series... I'll try to summarise my thinking
> tomorrow, but I do not see any obvious problem so far. Although I have some
> concerns about 5/6, I need to re-read it after sleep.
Sure.
>
>
> On 07/16, Ravi Bangoria wrote:
>>
>> +static int delayed_uprobe_install(struct vm_area_struct *vma)
>> +{
>> +struct list_head *pos, *q;
>> +struct delayed_uprobe *du;
>> +unsigned long vaddr;
>> +int ret = 0, err = 0;
>> +
>> +mutex_lock(_uprobe_lock);
>> +list_for_each_safe(pos, q, _uprobe_list) {
>> +du = list_entry(pos, struct delayed_uprobe, list);
>> +
>> +if (!du->uprobe->ref_ctr_offset ||
>
> Is it possible to see ->ref_ctr_offset == 0 in delayed_uprobe_list?
I'll remove this check.
>
>> @@ -1072,7 +1282,13 @@ int uprobe_mmap(struct vm_area_struct *vma)
>> struct uprobe *uprobe, *u;
>> struct inode *inode;
>>
>> -if (no_uprobe_events() || !valid_vma(vma, true))
>> +if (no_uprobe_events())
>> +return 0;
>> +
>> +if (vma->vm_flags & VM_WRITE)
>> +delayed_uprobe_install(vma);
>
> Obviously not nice performance-wise... OK, I do not know if it will actually
> hurt in practice and probably we can use the better data structures if
> necessary.
> But can't we check MMF_HAS_UPROBES at least? I mean,
>
> if (vma->vm_flags & VM_WRITE && test_bit(MMF_HAS_UPROBES,
> >vm_mm->flags))
> delayed_uprobe_install(vma);
>
> ?
Yes.
>
>
> Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by
> delayed_uprobe_add().
Yes, good idea.
Thanks for the review,
Ravi
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Hi Oleg,
On 07/23/2018 09:56 PM, Oleg Nesterov wrote:
> I have a mixed feeling about this series... I'll try to summarise my thinking
> tomorrow, but I do not see any obvious problem so far. Although I have some
> concerns about 5/6, I need to re-read it after sleep.
Sure.
>
>
> On 07/16, Ravi Bangoria wrote:
>>
>> +static int delayed_uprobe_install(struct vm_area_struct *vma)
>> +{
>> +struct list_head *pos, *q;
>> +struct delayed_uprobe *du;
>> +unsigned long vaddr;
>> +int ret = 0, err = 0;
>> +
>> +mutex_lock(_uprobe_lock);
>> +list_for_each_safe(pos, q, _uprobe_list) {
>> +du = list_entry(pos, struct delayed_uprobe, list);
>> +
>> +if (!du->uprobe->ref_ctr_offset ||
>
> Is it possible to see ->ref_ctr_offset == 0 in delayed_uprobe_list?
I'll remove this check.
>
>> @@ -1072,7 +1282,13 @@ int uprobe_mmap(struct vm_area_struct *vma)
>> struct uprobe *uprobe, *u;
>> struct inode *inode;
>>
>> -if (no_uprobe_events() || !valid_vma(vma, true))
>> +if (no_uprobe_events())
>> +return 0;
>> +
>> +if (vma->vm_flags & VM_WRITE)
>> +delayed_uprobe_install(vma);
>
> Obviously not nice performance-wise... OK, I do not know if it will actually
> hurt in practice and probably we can use the better data structures if
> necessary.
> But can't we check MMF_HAS_UPROBES at least? I mean,
>
> if (vma->vm_flags & VM_WRITE && test_bit(MMF_HAS_UPROBES,
> >vm_mm->flags))
> delayed_uprobe_install(vma);
>
> ?
Yes.
>
>
> Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by
> delayed_uprobe_add().
Yes, good idea.
Thanks for the review,
Ravi
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
I have a mixed feeling about this series... I'll try to summarise my thinking
tomorrow, but I do not see any obvious problem so far. Although I have some
concerns about 5/6, I need to re-read it after sleep.
On 07/16, Ravi Bangoria wrote:
>
> +static int delayed_uprobe_install(struct vm_area_struct *vma)
> +{
> + struct list_head *pos, *q;
> + struct delayed_uprobe *du;
> + unsigned long vaddr;
> + int ret = 0, err = 0;
> +
> + mutex_lock(_uprobe_lock);
> + list_for_each_safe(pos, q, _uprobe_list) {
> + du = list_entry(pos, struct delayed_uprobe, list);
> +
> + if (!du->uprobe->ref_ctr_offset ||
Is it possible to see ->ref_ctr_offset == 0 in delayed_uprobe_list?
> @@ -1072,7 +1282,13 @@ int uprobe_mmap(struct vm_area_struct *vma)
> struct uprobe *uprobe, *u;
> struct inode *inode;
>
> - if (no_uprobe_events() || !valid_vma(vma, true))
> + if (no_uprobe_events())
> + return 0;
> +
> + if (vma->vm_flags & VM_WRITE)
> + delayed_uprobe_install(vma);
Obviously not nice performance-wise... OK, I do not know if it will actually
hurt in practice and probably we can use the better data structures if
necessary.
But can't we check MMF_HAS_UPROBES at least? I mean,
if (vma->vm_flags & VM_WRITE && test_bit(MMF_HAS_UPROBES,
>vm_mm->flags))
delayed_uprobe_install(vma);
?
Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by
delayed_uprobe_add().
Oleg.
Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
I have a mixed feeling about this series... I'll try to summarise my thinking
tomorrow, but I do not see any obvious problem so far. Although I have some
concerns about 5/6, I need to re-read it after sleep.
On 07/16, Ravi Bangoria wrote:
>
> +static int delayed_uprobe_install(struct vm_area_struct *vma)
> +{
> + struct list_head *pos, *q;
> + struct delayed_uprobe *du;
> + unsigned long vaddr;
> + int ret = 0, err = 0;
> +
> + mutex_lock(_uprobe_lock);
> + list_for_each_safe(pos, q, _uprobe_list) {
> + du = list_entry(pos, struct delayed_uprobe, list);
> +
> + if (!du->uprobe->ref_ctr_offset ||
Is it possible to see ->ref_ctr_offset == 0 in delayed_uprobe_list?
> @@ -1072,7 +1282,13 @@ int uprobe_mmap(struct vm_area_struct *vma)
> struct uprobe *uprobe, *u;
> struct inode *inode;
>
> - if (no_uprobe_events() || !valid_vma(vma, true))
> + if (no_uprobe_events())
> + return 0;
> +
> + if (vma->vm_flags & VM_WRITE)
> + delayed_uprobe_install(vma);
Obviously not nice performance-wise... OK, I do not know if it will actually
hurt in practice and probably we can use the better data structures if
necessary.
But can't we check MMF_HAS_UPROBES at least? I mean,
if (vma->vm_flags & VM_WRITE && test_bit(MMF_HAS_UPROBES,
>vm_mm->flags))
delayed_uprobe_install(vma);
?
Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by
delayed_uprobe_add().
Oleg.
[PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Userspace Statically Defined Tracepoints[1] are dtrace style markers
inside userspace applications. Applications like PostgreSQL, MySQL,
Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc
have these markers embedded in them. These markers are added by developer
at important places in the code. Each marker source expands to a single
nop instruction in the compiled code but there may be additional
overhead for computing the marker arguments which expands to couple of
instructions. In case the overhead is more, execution of it can be
omitted by runtime if() condition when no one is tracing on the marker:
if (reference_counter > 0) {
Execute marker instructions;
}
Default value of reference counter is 0. Tracer has to increment the
reference counter before tracing on a marker and decrement it when
done with the tracing.
Implement the reference counter logic in core uprobe. User will be
able to use it from trace_uprobe as well as from kernel module. New
trace_uprobe definition with reference counter will now be:
:[(ref_ctr_offset)]
where ref_ctr_offset is an optional field. For kernel module, new
variant of uprobe_register() has been introduced:
uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer)
No new variant for uprobe_unregister() because it's assumed to have
only one reference counter for one uprobe.
[1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
Note: 'reference counter' is called as 'semaphore' in original Dtrace
(or Systemtap, bcc and even in ELF) documentation and code. But the
term 'semaphore' is misleading in this context. This is just a counter
used to hold number of tracers tracing on a marker. This is not really
used for any synchronization. So we are referring it as 'reference
counter' in kernel / perf code.
Signed-off-by: Ravi Bangoria
---
include/linux/uprobes.h | 5 +
kernel/events/uprobes.c | 232 ++--
kernel/trace/trace.c| 2 +-
kernel/trace/trace_uprobe.c | 38 +++-
4 files changed, 267 insertions(+), 10 deletions(-)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index bb9d2084af03..103a48a48872 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -123,6 +123,7 @@ extern unsigned long uprobe_get_swbp_addr(struct pt_regs
*regs);
extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct
*mm, unsigned long vaddr, uprobe_opcode_t);
extern int uprobe_register(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc);
+extern int uprobe_register_refctr(struct inode *inode, loff_t offset, loff_t
ref_ctr_offset, struct uprobe_consumer *uc);
extern int uprobe_apply(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc, bool);
extern void uprobe_unregister(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc);
extern int uprobe_mmap(struct vm_area_struct *vma);
@@ -160,6 +161,10 @@ uprobe_register(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc)
{
return -ENOSYS;
}
+static inline int uprobe_register_refctr(struct inode *inode, loff_t offset,
loff_t ref_ctr_offset, struct uprobe_consumer *uc)
+{
+ return -ENOSYS;
+}
static inline int
uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc,
bool add)
{
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c0418ba52ba8..84da8512a974 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -73,6 +73,7 @@ struct uprobe {
struct uprobe_consumer *consumers;
struct inode*inode; /* Also hold a ref to inode */
loff_t offset;
+ loff_t ref_ctr_offset;
unsigned long flags;
/*
@@ -88,6 +89,15 @@ struct uprobe {
struct arch_uprobe arch;
};
+struct delayed_uprobe {
+ struct list_head list;
+ struct uprobe *uprobe;
+ struct mm_struct *mm;
+};
+
+static DEFINE_MUTEX(delayed_uprobe_lock);
+static LIST_HEAD(delayed_uprobe_list);
+
/*
* Execute out of line area: anonymous executable mapping installed
* by the probed task to execute the copy of the original instruction
@@ -282,6 +292,154 @@ static int verify_opcode(struct page *page, unsigned long
vaddr, uprobe_opcode_t
return 1;
}
+static struct delayed_uprobe *
+delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
+{
+ struct delayed_uprobe *du;
+
+ list_for_each_entry(du, _uprobe_list, list)
+ if (du->uprobe == uprobe && du->mm == mm)
+ return du;
+ return NULL;
+}
+
+static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
+{
+ struct delayed_uprobe *du;
+
+ if (delayed_uprobe_check(uprobe, mm))
+ return 0;
+
+ du = kzalloc(sizeof(*du), GFP_KERNEL);
+
[PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Userspace Statically Defined Tracepoints[1] are dtrace style markers
inside userspace applications. Applications like PostgreSQL, MySQL,
Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc
have these markers embedded in them. These markers are added by developer
at important places in the code. Each marker source expands to a single
nop instruction in the compiled code but there may be additional
overhead for computing the marker arguments which expands to couple of
instructions. In case the overhead is more, execution of it can be
omitted by runtime if() condition when no one is tracing on the marker:
if (reference_counter > 0) {
Execute marker instructions;
}
Default value of reference counter is 0. Tracer has to increment the
reference counter before tracing on a marker and decrement it when
done with the tracing.
Implement the reference counter logic in core uprobe. User will be
able to use it from trace_uprobe as well as from kernel module. New
trace_uprobe definition with reference counter will now be:
:[(ref_ctr_offset)]
where ref_ctr_offset is an optional field. For kernel module, new
variant of uprobe_register() has been introduced:
uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer)
No new variant for uprobe_unregister() because it's assumed to have
only one reference counter for one uprobe.
[1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
Note: 'reference counter' is called as 'semaphore' in original Dtrace
(or Systemtap, bcc and even in ELF) documentation and code. But the
term 'semaphore' is misleading in this context. This is just a counter
used to hold number of tracers tracing on a marker. This is not really
used for any synchronization. So we are referring it as 'reference
counter' in kernel / perf code.
Signed-off-by: Ravi Bangoria
---
include/linux/uprobes.h | 5 +
kernel/events/uprobes.c | 232 ++--
kernel/trace/trace.c| 2 +-
kernel/trace/trace_uprobe.c | 38 +++-
4 files changed, 267 insertions(+), 10 deletions(-)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index bb9d2084af03..103a48a48872 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -123,6 +123,7 @@ extern unsigned long uprobe_get_swbp_addr(struct pt_regs
*regs);
extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct
*mm, unsigned long vaddr, uprobe_opcode_t);
extern int uprobe_register(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc);
+extern int uprobe_register_refctr(struct inode *inode, loff_t offset, loff_t
ref_ctr_offset, struct uprobe_consumer *uc);
extern int uprobe_apply(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc, bool);
extern void uprobe_unregister(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc);
extern int uprobe_mmap(struct vm_area_struct *vma);
@@ -160,6 +161,10 @@ uprobe_register(struct inode *inode, loff_t offset, struct
uprobe_consumer *uc)
{
return -ENOSYS;
}
+static inline int uprobe_register_refctr(struct inode *inode, loff_t offset,
loff_t ref_ctr_offset, struct uprobe_consumer *uc)
+{
+ return -ENOSYS;
+}
static inline int
uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc,
bool add)
{
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c0418ba52ba8..84da8512a974 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -73,6 +73,7 @@ struct uprobe {
struct uprobe_consumer *consumers;
struct inode*inode; /* Also hold a ref to inode */
loff_t offset;
+ loff_t ref_ctr_offset;
unsigned long flags;
/*
@@ -88,6 +89,15 @@ struct uprobe {
struct arch_uprobe arch;
};
+struct delayed_uprobe {
+ struct list_head list;
+ struct uprobe *uprobe;
+ struct mm_struct *mm;
+};
+
+static DEFINE_MUTEX(delayed_uprobe_lock);
+static LIST_HEAD(delayed_uprobe_list);
+
/*
* Execute out of line area: anonymous executable mapping installed
* by the probed task to execute the copy of the original instruction
@@ -282,6 +292,154 @@ static int verify_opcode(struct page *page, unsigned long
vaddr, uprobe_opcode_t
return 1;
}
+static struct delayed_uprobe *
+delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
+{
+ struct delayed_uprobe *du;
+
+ list_for_each_entry(du, _uprobe_list, list)
+ if (du->uprobe == uprobe && du->mm == mm)
+ return du;
+ return NULL;
+}
+
+static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
+{
+ struct delayed_uprobe *du;
+
+ if (delayed_uprobe_check(uprobe, mm))
+ return 0;
+
+ du = kzalloc(sizeof(*du), GFP_KERNEL);
+
