[v4] tracing: Make persistent ring buffer freeable

[PATCH v4 1/2] mm/memblock: Add reserved memory release function

Posted by Masami Hiramatsu (Google) 11 months, 3 weeks ago

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add reserve_mem_release_by_name() to release a reserved memory region
with a given name. This allows us to release reserved memory which is
defined by kernel cmdline, after boot.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
---
 Changes in v4:
  - Use free_reserved_area() according to Mike's comment.
 Changes in v2:
  - Rename reserved_mem_* to reserve_mem_*.
---
 include/linux/mm.h |    1 +
 mm/memblock.c      |   66 +++++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 55 insertions(+), 12 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7b1068ddcbb7..1ee9e7447485 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4123,6 +4123,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
 void vma_pgtable_walk_end(struct vm_area_struct *vma);
 
 int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
+int reserve_mem_release_by_name(const char *name);
 
 #ifdef CONFIG_64BIT
 int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
diff --git a/mm/memblock.c b/mm/memblock.c
index 95af35fd1389..8cd95f60015d 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -16,6 +16,7 @@
 #include <linux/kmemleak.h>
 #include <linux/seq_file.h>
 #include <linux/memblock.h>
+#include <linux/mutex.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -2283,6 +2284,7 @@ struct reserve_mem_table {
 };
 static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
 static int reserved_mem_count;
+static DEFINE_MUTEX(reserve_mem_lock);
 
 /* Add wildcard region with a lookup name */
 static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
@@ -2296,6 +2298,21 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
 	strscpy(map->name, name);
 }
 
+static struct reserve_mem_table *reserve_mem_find_by_name_nolock(const char *name)
+{
+	struct reserve_mem_table *map;
+	int i;
+
+	for (i = 0; i < reserved_mem_count; i++) {
+		map = &reserved_mem_table[i];
+		if (!map->size)
+			continue;
+		if (strcmp(name, map->name) == 0)
+			return map;
+	}
+	return NULL;
+}
+
 /**
  * reserve_mem_find_by_name - Find reserved memory region with a given name
  * @name: The name that is attached to a reserved memory region
@@ -2309,22 +2326,47 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
 int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
 {
 	struct reserve_mem_table *map;
-	int i;
 
-	for (i = 0; i < reserved_mem_count; i++) {
-		map = &reserved_mem_table[i];
-		if (!map->size)
-			continue;
-		if (strcmp(name, map->name) == 0) {
-			*start = map->start;
-			*size = map->size;
-			return 1;
-		}
-	}
-	return 0;
+	guard(mutex)(&reserve_mem_lock);
+	map = reserve_mem_find_by_name_nolock(name);
+	if (!map)
+		return 0;
+
+	*start = map->start;
+	*size = map->size;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
 
+/**
+ * reserve_mem_release_by_name - Release reserved memory region with a given name
+ * @name: The name that is attatched to a reserved memory region
+ *
+ * Forcibly release the pages in the reserved memory region so that those memory
+ * can be used as free memory. After released the reserved region size becomes 0.
+ *
+ * Returns: 1 if released or 0 if not found.
+ */
+int reserve_mem_release_by_name(const char *name)
+{
+	char buf[RESERVE_MEM_NAME_SIZE + 12];
+	struct reserve_mem_table *map;
+	void *start, *end;
+
+	guard(mutex)(&reserve_mem_lock);
+	map = reserve_mem_find_by_name_nolock(name);
+	if (!map)
+		return 0;
+
+	start = phys_to_virt(map->start);
+	end = start + map->size - 1;
+	snprintf(buf, sizeof(buf), "reserve_mem:%s", name);
+	free_reserved_area(start, end, 0, buf);
+	map->size = 0;
+
+	return 1;
+}
+
 /*
  * Parse reserve_mem=nn:align:name
  */

Re: [PATCH v4 1/2] mm/memblock: Add reserved memory release function

Posted by Wei Yang 10 months, 1 week ago

On Wed, Feb 19, 2025 at 12:08:58AM +0900, Masami Hiramatsu (Google) wrote:
>From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
>Add reserve_mem_release_by_name() to release a reserved memory region
>with a given name. This allows us to release reserved memory which is
>defined by kernel cmdline, after boot.
>
>Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: linux-mm@kvack.org
>---
> Changes in v4:
>  - Use free_reserved_area() according to Mike's comment.
> Changes in v2:
>  - Rename reserved_mem_* to reserve_mem_*.
>---
> include/linux/mm.h |    1 +
> mm/memblock.c      |   66 +++++++++++++++++++++++++++++++++++++++++++---------
> 2 files changed, 55 insertions(+), 12 deletions(-)
>
>diff --git a/include/linux/mm.h b/include/linux/mm.h
>index 7b1068ddcbb7..1ee9e7447485 100644
>--- a/include/linux/mm.h
>+++ b/include/linux/mm.h
>@@ -4123,6 +4123,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
> void vma_pgtable_walk_end(struct vm_area_struct *vma);
> 
> int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
>+int reserve_mem_release_by_name(const char *name);
> 
> #ifdef CONFIG_64BIT
> int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
>diff --git a/mm/memblock.c b/mm/memblock.c
>index 95af35fd1389..8cd95f60015d 100644
>--- a/mm/memblock.c
>+++ b/mm/memblock.c
>@@ -16,6 +16,7 @@
> #include <linux/kmemleak.h>
> #include <linux/seq_file.h>
> #include <linux/memblock.h>
>+#include <linux/mutex.h>
> 
> #include <asm/sections.h>
> #include <linux/io.h>
>@@ -2283,6 +2284,7 @@ struct reserve_mem_table {
> };
> static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
> static int reserved_mem_count;
>+static DEFINE_MUTEX(reserve_mem_lock);
> 

This looks break the memblock tests in tools/testing/memblock.

memblock.c:2289:8: warning: type defaults to ‘int’ in declaration of ‘DEFINE_MUTEX’ [-Wimplicit-int]
 2289 | static DEFINE_MUTEX(reserve_mem_lock);
      |        ^~~~~~~~~~~~
memblock.c:2289:1: warning: parameter names (without types) in function declaration
 2289 | static DEFINE_MUTEX(reserve_mem_lock);
      | ^~~~~~
memblock.c: In function ‘reserve_mem_find_by_name’:
memblock.c:2332:9: warning: implicit declaration of function ‘guard’ [-Wimplicit-function-declaration]
 2332 |         guard(mutex)(&reserve_mem_lock);
      |         ^~~~~

Re: [PATCH v4 1/2] mm/memblock: Add reserved memory release function

Posted by Masami Hiramatsu (Google) 10 months, 1 week ago

On Sat, 5 Apr 2025 02:30:18 +0000
Wei Yang <richard.weiyang@gmail.com> wrote:

> On Wed, Feb 19, 2025 at 12:08:58AM +0900, Masami Hiramatsu (Google) wrote:
> >From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >
> >Add reserve_mem_release_by_name() to release a reserved memory region
> >with a given name. This allows us to release reserved memory which is
> >defined by kernel cmdline, after boot.
> >
> >Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> >Cc: Andrew Morton <akpm@linux-foundation.org>
> >Cc: linux-mm@kvack.org
> >---
> > Changes in v4:
> >  - Use free_reserved_area() according to Mike's comment.
> > Changes in v2:
> >  - Rename reserved_mem_* to reserve_mem_*.
> >---
> > include/linux/mm.h |    1 +
> > mm/memblock.c      |   66 +++++++++++++++++++++++++++++++++++++++++++---------
> > 2 files changed, 55 insertions(+), 12 deletions(-)
> >
> >diff --git a/include/linux/mm.h b/include/linux/mm.h
> >index 7b1068ddcbb7..1ee9e7447485 100644
> >--- a/include/linux/mm.h
> >+++ b/include/linux/mm.h
> >@@ -4123,6 +4123,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
> > void vma_pgtable_walk_end(struct vm_area_struct *vma);
> > 
> > int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
> >+int reserve_mem_release_by_name(const char *name);
> > 
> > #ifdef CONFIG_64BIT
> > int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
> >diff --git a/mm/memblock.c b/mm/memblock.c
> >index 95af35fd1389..8cd95f60015d 100644
> >--- a/mm/memblock.c
> >+++ b/mm/memblock.c
> >@@ -16,6 +16,7 @@
> > #include <linux/kmemleak.h>
> > #include <linux/seq_file.h>
> > #include <linux/memblock.h>
> >+#include <linux/mutex.h>
> > 
> > #include <asm/sections.h>
> > #include <linux/io.h>
> >@@ -2283,6 +2284,7 @@ struct reserve_mem_table {
> > };
> > static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
> > static int reserved_mem_count;
> >+static DEFINE_MUTEX(reserve_mem_lock);
> > 
> 
> This looks break the memblock tests in tools/testing/memblock.
> 
> memblock.c:2289:8: warning: type defaults to ‘int’ in declaration of ‘DEFINE_MUTEX’ [-Wimplicit-int]
>  2289 | static DEFINE_MUTEX(reserve_mem_lock);
>       |        ^~~~~~~~~~~~
> memblock.c:2289:1: warning: parameter names (without types) in function declaration
>  2289 | static DEFINE_MUTEX(reserve_mem_lock);
>       | ^~~~~~
> memblock.c: In function ‘reserve_mem_find_by_name’:
> memblock.c:2332:9: warning: implicit declaration of function ‘guard’ [-Wimplicit-function-declaration]
>  2332 |         guard(mutex)(&reserve_mem_lock);
>       |         ^~~~~

Hmm, this means the memblock test builds the kernel source code in user
space. I think we need to add linux/mutex.h under tools/testing/memblock.

But this is fragile by design. As I did for lib/bootconfig and
tools/bootconfig, you should use __KERNEL__ and makes it not depending on
the kernel header files because it does not expected to be used in user
space.
Even if I added mutex.h, it stopped with another reason.

test -L linux/memblock.h || ln -s ../../../../include/linux/memblock.h linux/memblock.h
test -L asm/asm.h || ln -s ../../../arch/x86/include/asm/asm.h asm/asm.h
test -L asm/cmpxchg.h || ln -s ../../../arch/x86/include/asm/cmpxchg.h asm/cmpxchg.h
cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o main.o main.c
test -L memblock.c || ln -s ../../../mm/memblock.c memblock.c
cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o memblock.o memblock.c
memblock.c: In function 'memblock_add_range.isra':
memblock.c:685:17: warning: 'end_rgn' may be used uninitialized [-Wmaybe-uninitialized]
  685 |                 memblock_merge_regions(type, start_rgn, end_rgn);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
memblock.c:591:42: note: 'end_rgn' was declared here
  591 |         int idx, nr_new, start_rgn = -1, end_rgn;
      |                                          ^~~~~~~
cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o lib/slab.o lib/slab.c
cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o mmzone.o mmzone.c
cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o slab.o ../../lib/slab.c
../../lib/slab.c:6:10: fatal error: urcu/uatomic.h: No such file or directory
    6 | #include <urcu/uatomic.h>
      |          ^~~~~~~~~~~~~~~~
compilation terminated.
make: *** [<builtin>: slab.o] Error 1


Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH v4 1/2] mm/memblock: Add reserved memory release function

Posted by Masami Hiramatsu (Google) 10 months, 1 week ago

On Mon, 7 Apr 2025 09:33:51 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> But this is fragile by design. As I did for lib/bootconfig and
> tools/bootconfig, you should use __KERNEL__ and makes it not depending on
> the kernel header files because it does not expected to be used in user
> space.
> Even if I added mutex.h, it stopped with another reason.
> 
> test -L linux/memblock.h || ln -s ../../../../include/linux/memblock.h linux/memblock.h
> test -L asm/asm.h || ln -s ../../../arch/x86/include/asm/asm.h asm/asm.h
> test -L asm/cmpxchg.h || ln -s ../../../arch/x86/include/asm/cmpxchg.h asm/cmpxchg.h
> cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o main.o main.c
> test -L memblock.c || ln -s ../../../mm/memblock.c memblock.c
> cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o memblock.o memblock.c
> memblock.c: In function 'memblock_add_range.isra':
> memblock.c:685:17: warning: 'end_rgn' may be used uninitialized [-Wmaybe-uninitialized]
>   685 |                 memblock_merge_regions(type, start_rgn, end_rgn);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> memblock.c:591:42: note: 'end_rgn' was declared here
>   591 |         int idx, nr_new, start_rgn = -1, end_rgn;
>       |                                          ^~~~~~~
> cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o lib/slab.o lib/slab.c
> cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o mmzone.o mmzone.c
> cc -I. -I../../include -Wall -O2 -fsanitize=address -fsanitize=undefined -D CONFIG_PHYS_ADDR_T_64BIT   -c -o slab.o ../../lib/slab.c
> ../../lib/slab.c:6:10: fatal error: urcu/uatomic.h: No such file or directory
>     6 | #include <urcu/uatomic.h>
>       |          ^~~~~~~~~~~~~~~~
> compilation terminated.
> make: *** [<builtin>: slab.o] Error 1

Ah, sorry. This is from liburcu. I installed the package and fixes the issue.
Let me send the patch.

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v4 1/2] mm/memblock: Add reserved memory release function
[PATCH v4 2/2] tracing: Freeable reserved ring buffer