Re: [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

Re: [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Steven Rostedt]

On Tue, 11 Jul 2023 05:29:58 +0800
Zheng Yejian <zhengyejian1@huawei.com> wrote:

> As comments in ftrace_process_locs(), there may be NULL pointers in
> mcount_loc section:
>  > Some architecture linkers will pad between
>  > the different mcount_loc sections of different
>  > object files to satisfy alignments.
>  > Skip any NULL pointers.  
> 
> After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
> NULL pointers will be accounted when allocating ftrace pages but
> skipped before adding into ftrace pages, this may result in some
> pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra
> helper functions"), warning may occur at:
>   WARN_ON(pg->next);
> 
> So we may need to skip NULL pointers before allocating ftrace pages.
> 
> Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
> ---
>  kernel/trace/ftrace.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 3740aca79fe7..5b474165df31 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod,
>  	if (!count)
>  		return 0;
>  
> +	p = start;
> +	while (p < end) {
> +		/*
> +		 * Refer to conments below, there may be NULL pointers,
> +		 * skip them before allocating pages
> +		 */
> +		addr = ftrace_call_adjust(*p++);
> +		if (!addr)
> +			count--;
> +	}

My main concern about this is the added overhead during boot to process
this. There's 10s of thousands of functions, so this loop will be 10s of
thousands. I also don't like that this is an unconditional loop (meaning it
executes even when it is unnecessary to do so).


>  	/*
>  	 * Sorting mcount in vmlinux at build time depend on
>  	 * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in

How about something like this?

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b24c573934af..acd033371721 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6474,6 +6474,7 @@ static int ftrace_process_locs(struct module *mod,
 	struct ftrace_page *start_pg;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
+	unsigned long skipped = 0;
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
@@ -6536,8 +6537,10 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr)
+		if (!addr) {
+			skipped++;
 			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,12 +6554,24 @@ static int ftrace_process_locs(struct module *mod,
 		rec->ip = addr;
 	}
 
-	/* We should have used all pages */
-	WARN_ON(pg->next);
-
 	/* Assign the last page to ftrace_pages */
 	ftrace_pages = pg;
 
+	/* We should have used all pages unless we skipped some */
+	if (pg->next) {
+		WARN_ON(!skipped);
+		while (ftrace_pages->next) {
+			pg = ftrace_pages->next;
+			ftrace_pages->next = pg->next;
+			if (pg->records) {
+				free_pages((unsigned long)pg->records, pg->order);
+				ftrace_number_of_pages -= 1 << pg->order;
+			}
+			kfree(pg);
+			ftrace_number_of_groups--;
+		}
+	}
+
 	/*
 	 * We only need to disable interrupts on start up
 	 * because we are modifying code that an interrupt

[PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but
skipped before adding into ftrace pages, this may result in some
pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra
helper functions"), warning may occur at:
  WARN_ON(pg->next);

So we may need to skip NULL pointers before allocating ftrace pages.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
 kernel/trace/ftrace.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..5b474165df31 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod,
 	if (!count)
 		return 0;
 
+	p = start;
+	while (p < end) {
+		/*
+		 * Refer to conments below, there may be NULL pointers,
+		 * skip them before allocating pages
+		 */
+		addr = ftrace_call_adjust(*p++);
+		if (!addr)
+			count--;
+	}
 	/*
 	 * Sorting mcount in vmlinux at build time depend on
 	 * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in
-- 
2.25.1

Re: [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

On 2023/7/10 22:46, Steven Rostedt wrote:
> On Tue, 11 Jul 2023 05:29:58 +0800
> Zheng Yejian <zhengyejian1@huawei.com> wrote:
> 
>> As comments in ftrace_process_locs(), there may be NULL pointers in
>> mcount_loc section:
>>   > Some architecture linkers will pad between
>>   > the different mcount_loc sections of different
>>   > object files to satisfy alignments.
>>   > Skip any NULL pointers.
>>
>> After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
>> NULL pointers will be accounted when allocating ftrace pages but
>> skipped before adding into ftrace pages, this may result in some
>> pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra
>> helper functions"), warning may occur at:
>>    WARN_ON(pg->next);
>>
>> So we may need to skip NULL pointers before allocating ftrace pages.
>>
>> Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
>> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
>> ---
>>   kernel/trace/ftrace.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index 3740aca79fe7..5b474165df31 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod,
>>   	if (!count)
>>   		return 0;
>>   
>> +	p = start;
>> +	while (p < end) {
>> +		/*
>> +		 * Refer to conments below, there may be NULL pointers,
>> +		 * skip them before allocating pages
>> +		 */
>> +		addr = ftrace_call_adjust(*p++);
>> +		if (!addr)
>> +			count--;
>> +	}
> 
> My main concern about this is the added overhead during boot to process
> this. There's 10s of thousands of functions, so this loop will be 10s of
> thousands. I also don't like that this is an unconditional loop (meaning it
> executes even when it is unnecessary to do so).
> 

Agreed! The added overhead probably superfluousin in most cases.

> 
>>   	/*
>>   	 * Sorting mcount in vmlinux at build time depend on
>>   	 * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in
> 
> How about something like this?
> 
> -- Steve
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index b24c573934af..acd033371721 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6474,6 +6474,7 @@ static int ftrace_process_locs(struct module *mod,
>   	struct ftrace_page *start_pg;
>   	struct ftrace_page *pg;
>   	struct dyn_ftrace *rec;
> +	unsigned long skipped = 0;
>   	unsigned long count;
>   	unsigned long *p;
>   	unsigned long addr;
> @@ -6536,8 +6537,10 @@ static int ftrace_process_locs(struct module *mod,
>   		 * object files to satisfy alignments.
>   		 * Skip any NULL pointers.
>   		 */
> -		if (!addr)
> +		if (!addr) {
> +			skipped++;
>   			continue;
> +		}
>   
>   		end_offset = (pg->index+1) * sizeof(pg->records[0]);
>   		if (end_offset > PAGE_SIZE << pg->order) {
> @@ -6551,12 +6554,24 @@ static int ftrace_process_locs(struct module *mod,
>   		rec->ip = addr;
>   	}
>   
> -	/* We should have used all pages */
> -	WARN_ON(pg->next);
> -
>   	/* Assign the last page to ftrace_pages */
>   	ftrace_pages = pg;
>   
> +	/* We should have used all pages unless we skipped some */
> +	if (pg->next) {
> +		WARN_ON(!skipped);
> +		while (ftrace_pages->next) {
> +			pg = ftrace_pages->next;
> +			ftrace_pages->next = pg->next;
> +			if (pg->records) {
> +				free_pages((unsigned long)pg->records, pg->order);
> +				ftrace_number_of_pages -= 1 << pg->order;
> +			}
> +			kfree(pg);
> +			ftrace_number_of_groups--;
> +		}

Do we only need to free the pages that not being used?

> +	}
> +
>   	/*
>   	 * We only need to disable interrupts on start up
>   	 * because we are modifying code that an interrupt
> 

[PATCH v3] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After commit 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but skipped
before adding into ftrace pages, this may result in some pages not being
used. Then after commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
  WARN_ON(pg->next);

To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
Changes v2 -> v3: https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/
  - Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'

Changes v1 -> v2: https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/
  - As suggested by Steve, only warn for case that no pointers skipped
    but pages not used up then free those unused pages. But I move the
    free process after releasing ftrace_lock.

 kernel/trace/ftrace.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..e43e21a3d5fd 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6473,7 +6473,9 @@ static int ftrace_process_locs(struct module *mod,
 {
 	struct ftrace_page *start_pg;
 	struct ftrace_page *pg;
+	struct ftrace_page *pg_unuse = NULL;
 	struct dyn_ftrace *rec;
+	unsigned long skipped = 0;
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
@@ -6536,8 +6538,10 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr)
+		if (!addr) {
+			skipped++;
 			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,8 +6555,10 @@ static int ftrace_process_locs(struct module *mod,
 		rec->ip = addr;
 	}
 
-	/* We should have used all pages */
-	WARN_ON(pg->next);
+	if (pg->next) {
+		pg_unuse = pg->next;
+		pg->next = NULL;
+	}
 
 	/* Assign the last page to ftrace_pages */
 	ftrace_pages = pg;
@@ -6574,6 +6580,20 @@ static int ftrace_process_locs(struct module *mod,
  out:
 	mutex_unlock(&ftrace_lock);
 
+	/* We should have used all pages unless we skipped some */
+	if (pg_unuse) {
+		WARN_ON(!skipped);
+		while (pg_unuse) {
+			pg = pg_unuse;
+			pg_unuse = pg->next;
+			if (pg->records) {
+				free_pages((unsigned long)pg->records, pg->order);
+				ftrace_number_of_pages -= 1 << pg->order;
+			}
+			kfree(pg);
+			ftrace_number_of_groups--;
+		}
+	}
 	return ret;
 }
 
-- 
2.25.1

Re: [PATCH v2] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Steven Rostedt]

On Wed, 12 Jul 2023 04:16:30 +0800
Zheng Yejian <zhengyejian1@huawei.com> wrote:

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 3740aca79fe7..b46e539dc085 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6473,7 +6473,9 @@ static int ftrace_process_locs(struct module *mod,
>  {
>  	struct ftrace_page *start_pg;
>  	struct ftrace_page *pg;
> +	struct ftrace_page *pg_unuse = NULL;
>  	struct dyn_ftrace *rec;
> +	unsigned long skipped = 0;
>  	unsigned long count;
>  	unsigned long *p;
>  	unsigned long addr;

Nit, to keep the upside-down-xmas-tree format:

	struct ftrace_page *pg_unuse = NULL;
	struct ftrace_page *start_pg;
	struct ftrace_page *pg;
	struct dyn_ftrace *rec;
	unsigned long skipped = 0;
	unsigned long count;
	unsigned long *p;
	unsigned long addr;

-- Steve

[PATCH v2] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After commit 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but skipped
before adding into ftrace pages, this may result in some pages not being
used. Then after commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
  WARN_ON(pg->next);

To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
 kernel/trace/ftrace.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..b46e539dc085 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6473,7 +6473,9 @@ static int ftrace_process_locs(struct module *mod,
 {
 	struct ftrace_page *start_pg;
 	struct ftrace_page *pg;
+	struct ftrace_page *pg_unuse = NULL;
 	struct dyn_ftrace *rec;
+	unsigned long skipped = 0;
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
@@ -6536,8 +6538,10 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr)
+		if (!addr) {
+			skipped++;
 			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,9 +6555,8 @@ static int ftrace_process_locs(struct module *mod,
 		rec->ip = addr;
 	}
 
-	/* We should have used all pages */
-	WARN_ON(pg->next);
-
+	pg_unuse = pg->next;
+	pg->next = NULL;
 	/* Assign the last page to ftrace_pages */
 	ftrace_pages = pg;
 
@@ -6574,6 +6577,20 @@ static int ftrace_process_locs(struct module *mod,
  out:
 	mutex_unlock(&ftrace_lock);
 
+	/* We should have used all pages unless we skipped some */
+	if (pg_unuse) {
+		WARN_ON(!skipped);
+		while (pg_unuse) {
+			pg = pg_unuse;
+			pg_unuse = pg->next;
+			if (pg->records) {
+				free_pages((unsigned long)pg->records, pg->order);
+				ftrace_number_of_pages -= 1 << pg->order;
+			}
+			kfree(pg);
+			ftrace_number_of_groups--;
+		}
+	}
 	return ret;
 }
 
-- 
2.25.1

[PATCH v4] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After commit 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but skipped
before adding into ftrace pages, this may result in some pages not being
used. Then after commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
  WARN_ON(pg->next);

To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
Changes v3 [3] => v4:
  - Keep the upside-down-xmas-tree format as Steve suggested.
    Link: https://lore.kernel.org/all/20230711095802.71406422@gandalf.local.home/

Changes v2 [2] => v3:
  - Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'.

Changes v1 [1] => v2:
  - As Steve suggested, only warn for case that no pointers skipped
    but pages not used up then free those unused pages. But I move
    the free process after releasing ftrace_lock.
    Link: https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/
  - Update commit messages about the new solution.

[1] https://lore.kernel.org/all/20230710212958.274126-1-zhengyejian1@huawei.com/
[2] https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/
[3] https://lore.kernel.org/all/20230711112752.2595316-1-zhengyejian1@huawei.com/

 kernel/trace/ftrace.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..6fc238f6ef3e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6471,9 +6471,11 @@ static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
 {
+	struct ftrace_page *pg_unuse = NULL;
 	struct ftrace_page *start_pg;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
+	unsigned long skipped = 0;
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
@@ -6536,8 +6538,10 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr)
+		if (!addr) {
+			skipped++;
 			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,8 +6555,10 @@ static int ftrace_process_locs(struct module *mod,
 		rec->ip = addr;
 	}
 
-	/* We should have used all pages */
-	WARN_ON(pg->next);
+	if (pg->next) {
+		pg_unuse = pg->next;
+		pg->next = NULL;
+	}
 
 	/* Assign the last page to ftrace_pages */
 	ftrace_pages = pg;
@@ -6574,6 +6580,20 @@ static int ftrace_process_locs(struct module *mod,
  out:
 	mutex_unlock(&ftrace_lock);
 
+	/* We should have used all pages unless we skipped some */
+	if (pg_unuse) {
+		WARN_ON(!skipped);
+		while (pg_unuse) {
+			pg = pg_unuse;
+			pg_unuse = pg->next;
+			if (pg->records) {
+				free_pages((unsigned long)pg->records, pg->order);
+				ftrace_number_of_pages -= 1 << pg->order;
+			}
+			kfree(pg);
+			ftrace_number_of_groups--;
+		}
+	}
 	return ret;
 }
 
-- 
2.25.1

[PATCH v5] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Zheng Yejian]

As comments in ftrace_process_locs(), there may be NULL pointers in
mcount_loc section:
 > Some architecture linkers will pad between
 > the different mcount_loc sections of different
 > object files to satisfy alignments.
 > Skip any NULL pointers.

After commit 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"),
NULL pointers will be accounted when allocating ftrace pages but skipped
before adding into ftrace pages, this may result in some pages not being
used. Then after commit 706c81f87f84 ("ftrace: Remove extra helper
functions"), warning may occur at:
  WARN_ON(pg->next);

To fix it, only warn for case that no pointers skipped but pages not used
up, then free those unused pages after releasing ftrace_lock.

Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
Changes v4 [6] => v5:
  - Extract page free logic in ftrace_allocate_pages() as ftrace_free_pages(),
    then call it to free unused pages in ftrace_process_locs().

Changes v3 [3] => v4:
  - Keep the upside-down-xmas-tree format as Steve suggested [5].

Changes v2 [2] => v3:
  - Check NULL for 'pg->next' before assigning it to variable 'pg_unuse'.

Changes v1 [1] => v2:
  - As Steve suggested [4], only warn for case that no pointers skipped
    but pages not used up then free those unused pages. But I move
    the free process after releasing ftrace_lock.
  - Update commit messages about the new solution.

[1] https://lore.kernel.org/all/20230710212958.274126-1-zhengyejian1@huawei.com/
[2] https://lore.kernel.org/all/20230711201630.1837109-1-zhengyejian1@huawei.com/
[3] https://lore.kernel.org/all/20230711112752.2595316-1-zhengyejian1@huawei.com/
[4] https://lore.kernel.org/all/20230710104625.421c851a@gandalf.local.home/
[5] https://lore.kernel.org/all/20230711095802.71406422@gandalf.local.home/
[6] https://lore.kernel.org/all/20230712013103.3021978-1-zhengyejian1@huawei.com/

 kernel/trace/ftrace.c | 45 +++++++++++++++++++++++++++++--------------
 1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3740aca79fe7..05c0024815bf 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3305,6 +3305,22 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count)
 	return cnt;
 }
 
+static void ftrace_free_pages(struct ftrace_page *pages)
+{
+	struct ftrace_page *pg = pages;
+
+	while (pg) {
+		if (pg->records) {
+			free_pages((unsigned long)pg->records, pg->order);
+			ftrace_number_of_pages -= 1 << pg->order;
+		}
+		pages = pg->next;
+		kfree(pg);
+		pg = pages;
+		ftrace_number_of_groups--;
+	}
+}
+
 static struct ftrace_page *
 ftrace_allocate_pages(unsigned long num_to_init)
 {
@@ -3343,17 +3359,7 @@ ftrace_allocate_pages(unsigned long num_to_init)
 	return start_pg;
 
  free_pages:
-	pg = start_pg;
-	while (pg) {
-		if (pg->records) {
-			free_pages((unsigned long)pg->records, pg->order);
-			ftrace_number_of_pages -= 1 << pg->order;
-		}
-		start_pg = pg->next;
-		kfree(pg);
-		pg = start_pg;
-		ftrace_number_of_groups--;
-	}
+	ftrace_free_pages(start_pg);
 	pr_info("ftrace: FAILED to allocate memory for functions\n");
 	return NULL;
 }
@@ -6471,9 +6477,11 @@ static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
 {
+	struct ftrace_page *pg_unuse = NULL;
 	struct ftrace_page *start_pg;
 	struct ftrace_page *pg;
 	struct dyn_ftrace *rec;
+	unsigned long skipped = 0;
 	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
@@ -6536,8 +6544,10 @@ static int ftrace_process_locs(struct module *mod,
 		 * object files to satisfy alignments.
 		 * Skip any NULL pointers.
 		 */
-		if (!addr)
+		if (!addr) {
+			skipped++;
 			continue;
+		}
 
 		end_offset = (pg->index+1) * sizeof(pg->records[0]);
 		if (end_offset > PAGE_SIZE << pg->order) {
@@ -6551,8 +6561,10 @@ static int ftrace_process_locs(struct module *mod,
 		rec->ip = addr;
 	}
 
-	/* We should have used all pages */
-	WARN_ON(pg->next);
+	if (pg->next) {
+		pg_unuse = pg->next;
+		pg->next = NULL;
+	}
 
 	/* Assign the last page to ftrace_pages */
 	ftrace_pages = pg;
@@ -6574,6 +6586,11 @@ static int ftrace_process_locs(struct module *mod,
  out:
 	mutex_unlock(&ftrace_lock);
 
+	/* We should have used all pages unless we skipped some */
+	if (pg_unuse) {
+		WARN_ON(!skipped);
+		ftrace_free_pages(pg_unuse);
+	}
 	return ret;
 }
 
-- 
2.25.1

Re: [PATCH v5] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs()

[Steven Rostedt]

On Wed, 12 Jul 2023 14:04:52 +0800
Zheng Yejian <zhengyejian1@huawei.com> wrote:

> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -3305,6 +3305,22 @@ static int ftrace_allocate_records(struct ftrace_page *pg, int count)
>  	return cnt;
>  }
>  
> +static void ftrace_free_pages(struct ftrace_page *pages)
> +{
> +	struct ftrace_page *pg = pages;
> +
> +	while (pg) {
> +		if (pg->records) {
> +			free_pages((unsigned long)pg->records, pg->order);
> +			ftrace_number_of_pages -= 1 << pg->order;
> +		}
> +		pages = pg->next;
> +		kfree(pg);
> +		pg = pages;
> +		ftrace_number_of_groups--;
> +	}
> +}
> +
>  static struct ftrace_page *
>  ftrace_allocate_pages(unsigned long num_to_init)
>  {
> @@ -3343,17 +3359,7 @@ ftrace_allocate_pages(unsigned long num_to_init)
>  	return start_pg;
>  
>   free_pages:
> -	pg = start_pg;
> -	while (pg) {
> -		if (pg->records) {
> -			free_pages((unsigned long)pg->records, pg->order);
> -			ftrace_number_of_pages -= 1 << pg->order;
> -		}
> -		start_pg = pg->next;
> -		kfree(pg);
> -		pg = start_pg;
> -		ftrace_number_of_groups--;
> -	}
> +	ftrace_free_pages(start_pg);
>  	pr_info("ftrace: FAILED to allocate memory for functions\n");
>  	return NULL;
>  }

Nice little clean up. I had already started testing your previous patch,
but due to my test machine running out of disk space (perf doesn't clean up
its .debug directory :-p), I have to rerun it.

I'll apply this one for the new testing.

Thanks!

-- Steve