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Date: Wed, 14 Mar 2018 23:15:40 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc: oleg@...hat.com, peterz@...radead.org, srikar@...ux.vnet.ibm.com,
acme@...nel.org, ananth@...ux.vnet.ibm.com,
akpm@...ux-foundation.org, alexander.shishkin@...ux.intel.com,
alexis.berlemont@...il.com, corbet@....net,
dan.j.williams@...el.com, gregkh@...uxfoundation.org,
huawei.libin@...wei.com, hughd@...gle.com, jack@...e.cz,
jglisse@...hat.com, jolsa@...hat.com, kan.liang@...el.com,
kirill.shutemov@...ux.intel.com, kjlx@...pleofstupid.com,
kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
milian.wolff@...b.com, mingo@...hat.com, namhyung@...nel.org,
naveen.n.rao@...ux.vnet.ibm.com, pc@...ibm.com,
pombredanne@...b.com, rostedt@...dmis.org, tglx@...utronix.de,
tmricht@...ux.vnet.ibm.com, willy@...radead.org,
yao.jin@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same
reference counter
On Tue, 13 Mar 2018 18:26:01 +0530
Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:
> For tiny binaries/libraries, different mmap regions points to the
> same file portion. In such cases, we may increment reference counter
> multiple times. But while de-registration, reference counter will get
> decremented only by once leaving reference counter > 0 even if no one
> is tracing on that marker.
>
> Ensure increment and decrement happens in sync by keeping list of
> mms in trace_uprobe. Increment reference counter only if mm is not
> present in the list and decrement only if mm is present in the list.
>
> Example
>
> # echo "p:sdt_tick/loop2 /tmp/tick:0x6e4(0x10036)" > uprobe_events
>
> Before patch:
>
> # perf stat -a -e sdt_tick:loop2
> # /tmp/tick
> # dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
> 0000000: 02 .
>
> # pkill perf
> # dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
> 0000000: 01 .
>
> After patch:
>
> # perf stat -a -e sdt_tick:loop2
> # /tmp/tick
> # dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
> 0000000: 01 .
>
> # pkill perf
> # dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
> 0000000: 00 .
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> ---
> kernel/trace/trace_uprobe.c | 105 +++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 103 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index b6c9b48..9bf3f7a 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -50,6 +50,11 @@ struct trace_uprobe_filter {
> struct list_head perf_events;
> };
>
> +struct sdt_mm_list {
> + struct mm_struct *mm;
> + struct sdt_mm_list *next;
> +};
Oh, please use struct list_head instead of defining your own pointer-chain :(
> +
> /*
> * uprobe event core functions
> */
> @@ -61,6 +66,8 @@ struct trace_uprobe {
> char *filename;
> unsigned long offset;
> unsigned long ref_ctr_offset;
> + struct sdt_mm_list *sml;
> + struct rw_semaphore sml_rw_sem;
BTW, is there any reason to use rw_semaphore? (mutex doesn't fit?)
Thank you,
> unsigned long nhit;
> struct trace_probe tp;
> };
> @@ -274,6 +281,7 @@ static inline bool is_ret_probe(struct trace_uprobe *tu)
> if (is_ret)
> tu->consumer.ret_handler = uretprobe_dispatcher;
> init_trace_uprobe_filter(&tu->filter);
> + init_rwsem(&tu->sml_rw_sem);
> return tu;
>
> error:
> @@ -921,6 +929,74 @@ static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
> return trace_handle_return(s);
> }
>
> +static bool sdt_check_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
> +{
> + struct sdt_mm_list *tmp = tu->sml;
> +
> + if (!tu->sml || !mm)
> + return false;
> +
> + while (tmp) {
> + if (tmp->mm == mm)
> + return true;
> + tmp = tmp->next;
> + }
> +
> + return false;
> +}
> +
> +static void sdt_add_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
> +{
> + struct sdt_mm_list *tmp;
> +
> + tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);
> + if (!tmp)
> + return;
> +
> + tmp->mm = mm;
> + tmp->next = tu->sml;
> + tu->sml = tmp;
> +}
> +
> +static void sdt_del_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
> +{
> + struct sdt_mm_list *prev, *curr;
> +
> + if (!tu->sml)
> + return;
> +
> + if (tu->sml->mm == mm) {
> + curr = tu->sml;
> + tu->sml = tu->sml->next;
> + kfree(curr);
> + return;
> + }
> +
> + prev = tu->sml;
> + curr = tu->sml->next;
> + while (curr) {
> + if (curr->mm == mm) {
> + prev->next = curr->next;
> + kfree(curr);
> + return;
> + }
> + prev = curr;
> + curr = curr->next;
> + }
> +}
> +
> +static void sdt_flush_mm_list(struct trace_uprobe *tu)
> +{
> + struct sdt_mm_list *next, *curr = tu->sml;
> +
> + while (curr) {
> + next = curr->next;
> + kfree(curr);
> + curr = next;
> + }
> + tu->sml = NULL;
> +}
> +
> static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma)
> {
> unsigned long vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> @@ -989,17 +1065,25 @@ static void sdt_increment_ref_ctr(struct trace_uprobe *tu)
> if (IS_ERR(info))
> goto out;
>
> + down_write(&tu->sml_rw_sem);
> while (info) {
> + if (sdt_check_mm_list(tu, info->mm))
> + goto cont;
> +
> down_write(&info->mm->mmap_sem);
>
> vma = sdt_find_vma(info->mm, tu);
> vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> - sdt_update_ref_ctr(info->mm, vaddr, 1);
> + if (!sdt_update_ref_ctr(info->mm, vaddr, 1))
> + sdt_add_mm_list(tu, info->mm);
>
> up_write(&info->mm->mmap_sem);
> +
> +cont:
> mmput(info->mm);
> info = uprobe_free_map_info(info);
> }
> + up_write(&tu->sml_rw_sem);
>
> out:
> uprobe_end_dup_mmap();
> @@ -1020,8 +1104,16 @@ void trace_uprobe_mmap_callback(struct vm_area_struct *vma)
> !trace_probe_is_enabled(&tu->tp))
> continue;
>
> + down_write(&tu->sml_rw_sem);
> + if (sdt_check_mm_list(tu, vma->vm_mm))
> + goto cont;
> +
> vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> - sdt_update_ref_ctr(vma->vm_mm, vaddr, 1);
> + if (!sdt_update_ref_ctr(vma->vm_mm, vaddr, 1))
> + sdt_add_mm_list(tu, vma->vm_mm);
> +
> +cont:
> + up_write(&tu->sml_rw_sem);
> }
> mutex_unlock(&uprobe_lock);
> }
> @@ -1038,7 +1130,11 @@ static void sdt_decrement_ref_ctr(struct trace_uprobe *tu)
> if (IS_ERR(info))
> goto out;
>
> + down_write(&tu->sml_rw_sem);
> while (info) {
> + if (!sdt_check_mm_list(tu, info->mm))
> + goto cont;
> +
> down_write(&info->mm->mmap_sem);
>
> vma = sdt_find_vma(info->mm, tu);
> @@ -1046,9 +1142,14 @@ static void sdt_decrement_ref_ctr(struct trace_uprobe *tu)
> sdt_update_ref_ctr(info->mm, vaddr, -1);
>
> up_write(&info->mm->mmap_sem);
> + sdt_del_mm_list(tu, info->mm);
> +
> +cont:
> mmput(info->mm);
> info = uprobe_free_map_info(info);
> }
> + sdt_flush_mm_list(tu);
> + up_write(&tu->sml_rw_sem);
>
> out:
> uprobe_end_dup_mmap();
> --
> 1.8.3.1
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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