diff mbox series

[bpf] bpf: Fix nested bpf_bprintf_prepare with more per-cpu buffers

Message ID 20210510213709.2004366-1-revest@chromium.org (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf] bpf: Fix nested bpf_bprintf_prepare with more per-cpu buffers | expand

Checks

Context Check Description
netdev/cover_letter success Link
netdev/fixes_present success Link
netdev/patch_count success Link
netdev/tree_selection success Clearly marked for bpf
netdev/subject_prefix success Link
netdev/cc_maintainers warning 5 maintainers not CCed: netdev@vger.kernel.org yhs@fb.com kafai@fb.com john.fastabend@gmail.com songliubraving@fb.com
netdev/source_inline success Was 0 now: 0
netdev/verify_signedoff success Link
netdev/module_param success Was 0 now: 0
netdev/build_32bit fail Errors and warnings before: 6 this patch: 6
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/verify_fixes success Link
netdev/checkpatch warning CHECK: Please use a blank line after function/struct/union/enum declarations
netdev/build_allmodconfig_warn fail Errors and warnings before: 6 this patch: 6
netdev/header_inline success Link

Commit Message

Florent Revest May 10, 2021, 9:37 p.m. UTC 
The bpf_seq_printf, bpf_trace_printk and bpf_snprintf helpers share one
per-cpu buffer that they use to store temporary data (arguments to
bprintf). They "get" that buffer with try_get_fmt_tmp_buf and "put" it
by the end of their scope with bpf_bprintf_cleanup.

If one of these helpers gets called within the scope of one of these
helpers, for example: a first bpf program gets called, uses
bpf_trace_printk which calls raw_spin_lock_irqsave which is traced by
another bpf program that calls bpf_snprintf, then the second "get"
fails. Essentially, these helpers are not re-entrant. They would return
-EBUSY and print a warning message once.

This patch triples the number of bprintf buffers to allow three levels
of nesting. This is very similar to what was done for tracepoints in
"9594dc3c7e7 bpf: fix nested bpf tracepoints with per-cpu data"

Fixes: d9c9e4db186a ("bpf: Factorize bpf_trace_printk and bpf_seq_printf")
Reported-by: syzbot+63122d0bc347f18c1884@syzkaller.appspotmail.com
Signed-off-by: Florent Revest <revest@chromium.org>
---
 kernel/bpf/helpers.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

Comments

kernel test robot May 11, 2021, 1:21 a.m. UTC | #1 
Hi Florent,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf/master]

url:    https://github.com/0day-ci/linux/commits/Florent-Revest/bpf-Fix-nested-bpf_bprintf_prepare-with-more-per-cpu-buffers/20210511-053835
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
config: powerpc-randconfig-r021-20210510 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a0fed635fe1701470062495a6ffee1c608f3f1bc)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install powerpc cross compiling tool for clang build
        # apt-get install binutils-powerpc-linux-gnu
        # https://github.com/0day-ci/linux/commit/1f5d45d9243d8ca8ece81e778579fc46a1946887
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Florent-Revest/bpf-Fix-nested-bpf_bprintf_prepare-with-more-per-cpu-buffers/20210511-053835
        git checkout 1f5d45d9243d8ca8ece81e778579fc46a1946887
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=powerpc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:265:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr)       raw_cpu_ptr(ptr)
                                               ^
   include/linux/percpu-defs.h:264:38: note: expanded from macro 'raw_cpu_ptr'
   #define raw_cpu_ptr(ptr)        per_cpu_ptr(ptr, 0)
                                               ^
   include/linux/percpu-defs.h:263:65: note: expanded from macro 'per_cpu_ptr'
   #define per_cpu_ptr(ptr, cpu)   ({ (void)(cpu); VERIFY_PERCPU_PTR(ptr); })
                                                                     ^
   include/linux/percpu-defs.h:259:20: note: expanded from macro 'VERIFY_PERCPU_PTR'
           __verify_pcpu_ptr(__p);                                         \
                             ^
   include/linux/percpu-defs.h:219:47: note: expanded from macro '__verify_pcpu_ptr'
           const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
                                                        ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
>> kernel/bpf/helpers.c:718:9: error: arithmetic on a pointer to an incomplete type 'typeof(struct bpf_bprintf_bufs)' (aka 'struct bpf_bprintf_bufs')
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:265:27: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr)       raw_cpu_ptr(ptr)
                                   ^~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:264:26: note: expanded from macro 'raw_cpu_ptr'
   #define raw_cpu_ptr(ptr)        per_cpu_ptr(ptr, 0)
                                   ^~~~~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:263:47: note: expanded from macro 'per_cpu_ptr'
   #define per_cpu_ptr(ptr, cpu)   ({ (void)(cpu); VERIFY_PERCPU_PTR(ptr); })
                                                   ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:259:2: note: expanded from macro 'VERIFY_PERCPU_PTR'
           __verify_pcpu_ptr(__p);                                         \
           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:219:52: note: expanded from macro '__verify_pcpu_ptr'
           const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
                                                       ~~~~~ ^
   kernel/bpf/helpers.c:703:30: note: forward declaration of 'struct bpf_bprintf_bufs'
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                ^
>> kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:265:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr)       raw_cpu_ptr(ptr)
                                               ^
   include/linux/percpu-defs.h:264:38: note: expanded from macro 'raw_cpu_ptr'
   #define raw_cpu_ptr(ptr)        per_cpu_ptr(ptr, 0)
                                               ^
   include/linux/percpu-defs.h:263:65: note: expanded from macro 'per_cpu_ptr'
   #define per_cpu_ptr(ptr, cpu)   ({ (void)(cpu); VERIFY_PERCPU_PTR(ptr); })
                                                                     ^
   include/linux/percpu-defs.h:260:12: note: expanded from macro 'VERIFY_PERCPU_PTR'
           (typeof(*(__p)) __kernel __force *)(__p);                       \
                     ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
>> kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:265:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr)       raw_cpu_ptr(ptr)
                                               ^
   include/linux/percpu-defs.h:264:38: note: expanded from macro 'raw_cpu_ptr'
   #define raw_cpu_ptr(ptr)        per_cpu_ptr(ptr, 0)
                                               ^
   include/linux/percpu-defs.h:263:65: note: expanded from macro 'per_cpu_ptr'
   #define per_cpu_ptr(ptr, cpu)   ({ (void)(cpu); VERIFY_PERCPU_PTR(ptr); })
                                                                     ^
   include/linux/percpu-defs.h:260:38: note: expanded from macro 'VERIFY_PERCPU_PTR'
           (typeof(*(__p)) __kernel __force *)(__p);                       \
                                               ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
>> kernel/bpf/helpers.c:718:7: error: incompatible pointer types assigning to 'struct bpf_bprintf_buffers *' from 'typeof (*(&bpf_bprintf_bufs)) *' (aka 'struct bpf_bprintf_bufs *') [-Werror,-Wincompatible-pointer-types]
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> kernel/bpf/helpers.c:703:48: error: tentative definition has type 'typeof(struct bpf_bprintf_bufs)' (aka 'struct bpf_bprintf_bufs') that is never completed
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
   kernel/bpf/helpers.c:703:30: note: forward declaration of 'struct bpf_bprintf_bufs'
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                ^
   6 errors generated.


vim +718 kernel/bpf/helpers.c

   698	
   699	/* Support executing three nested bprintf helper calls on a given CPU */
   700	struct bpf_bprintf_buffers {
   701		char tmp_bufs[3][MAX_PRINTF_BUF_LEN];
   702	};
 > 703	static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
   704	static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
   705	
   706	static int try_get_fmt_tmp_buf(char **tmp_buf)
   707	{
   708		struct bpf_bprintf_buffers *bufs;
   709		int nest_level;
   710	
   711		preempt_disable();
   712		nest_level = this_cpu_inc_return(bpf_bprintf_nest_level);
   713		if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
   714			this_cpu_dec(bpf_bprintf_nest_level);
   715			preempt_enable();
   716			return -EBUSY;
   717		}
 > 718		bufs = this_cpu_ptr(&bpf_bprintf_buf);
   719		*tmp_buf = bufs->tmp_bufs[nest_level - 1];
   720	
   721		return 0;
   722	}
   723	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
kernel test robot May 11, 2021, 1:57 a.m. UTC | #2 
Hi Florent,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf/master]

url:    https://github.com/0day-ci/linux/commits/Florent-Revest/bpf-Fix-nested-bpf_bprintf_prepare-with-more-per-cpu-buffers/20210511-053835
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
config: s390-randconfig-r013-20210510 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a0fed635fe1701470062495a6ffee1c608f3f1bc)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        # https://github.com/0day-ci/linux/commit/1f5d45d9243d8ca8ece81e778579fc46a1946887
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Florent-Revest/bpf-Fix-nested-bpf_bprintf_prepare-with-more-per-cpu-buffers/20210511-053835
        git checkout 1f5d45d9243d8ca8ece81e778579fc46a1946887
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=s390 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   include/linux/percpu-defs.h:252:27: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
                             ^~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:241:2: note: expanded from macro 'raw_cpu_ptr'
           __verify_pcpu_ptr(ptr);                                         \
           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/percpu-defs.h:219:52: note: expanded from macro '__verify_pcpu_ptr'
           const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
                                                       ~~~~~ ^
   kernel/bpf/helpers.c:703:30: note: forward declaration of 'struct bpf_bprintf_bufs'
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                ^
   kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:252:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
                                         ^
   include/linux/percpu-defs.h:242:19: note: expanded from macro 'raw_cpu_ptr'
           arch_raw_cpu_ptr(ptr);                                          \
                            ^
   include/asm-generic/percpu.h:44:48: note: expanded from macro 'arch_raw_cpu_ptr'
   #define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
                                                  ^
   include/linux/percpu-defs.h:231:23: note: expanded from macro 'SHIFT_PERCPU_PTR'
           RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
                                ^
   include/linux/compiler.h:181:31: note: expanded from macro 'RELOC_HIDE'
        __ptr = (unsigned long) (ptr);                             \
                                 ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
   kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:252:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
                                         ^
   include/linux/percpu-defs.h:242:19: note: expanded from macro 'raw_cpu_ptr'
           arch_raw_cpu_ptr(ptr);                                          \
                            ^
   include/asm-generic/percpu.h:44:48: note: expanded from macro 'arch_raw_cpu_ptr'
   #define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
                                                  ^
   include/linux/percpu-defs.h:231:49: note: expanded from macro 'SHIFT_PERCPU_PTR'
           RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
                                                          ^
   include/linux/compiler.h:181:31: note: expanded from macro 'RELOC_HIDE'
        __ptr = (unsigned long) (ptr);                             \
                                 ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
   kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:252:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
                                         ^
   include/linux/percpu-defs.h:242:19: note: expanded from macro 'raw_cpu_ptr'
           arch_raw_cpu_ptr(ptr);                                          \
                            ^
   include/asm-generic/percpu.h:44:48: note: expanded from macro 'arch_raw_cpu_ptr'
   #define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
                                                  ^
   include/linux/percpu-defs.h:231:23: note: expanded from macro 'SHIFT_PERCPU_PTR'
           RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
                                ^
   include/linux/compiler.h:182:13: note: expanded from macro 'RELOC_HIDE'
       (typeof(ptr)) (__ptr + (off)); })
               ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
   kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                                ^~~~~~~~~~~~~~~
                                bpf_bprintf_bufs
   include/linux/percpu-defs.h:252:39: note: expanded from macro 'this_cpu_ptr'
   #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
                                         ^
   include/linux/percpu-defs.h:242:19: note: expanded from macro 'raw_cpu_ptr'
           arch_raw_cpu_ptr(ptr);                                          \
                            ^
   include/asm-generic/percpu.h:44:48: note: expanded from macro 'arch_raw_cpu_ptr'
   #define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
                                                  ^
   include/linux/percpu-defs.h:231:49: note: expanded from macro 'SHIFT_PERCPU_PTR'
           RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
                                                          ^
   include/linux/compiler.h:182:13: note: expanded from macro 'RELOC_HIDE'
       (typeof(ptr)) (__ptr + (off)); })
               ^
   kernel/bpf/helpers.c:703:48: note: 'bpf_bprintf_bufs' declared here
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
>> kernel/bpf/helpers.c:718:7: error: incompatible pointer types assigning to 'struct bpf_bprintf_buffers *' from 'typeof ((typeof (*(&bpf_bprintf_bufs)) *)(&bpf_bprintf_bufs))' (aka 'struct bpf_bprintf_bufs *') [-Werror,-Wincompatible-pointer-types]
           bufs = this_cpu_ptr(&bpf_bprintf_buf);
                ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/bpf/helpers.c:703:48: error: tentative definition has type 'typeof(struct bpf_bprintf_bufs)' (aka 'struct bpf_bprintf_bufs') that is never completed
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                                  ^
   kernel/bpf/helpers.c:703:30: note: forward declaration of 'struct bpf_bprintf_bufs'
   static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
                                ^
   12 warnings and 8 errors generated.


vim +718 kernel/bpf/helpers.c

   705	
   706	static int try_get_fmt_tmp_buf(char **tmp_buf)
   707	{
   708		struct bpf_bprintf_buffers *bufs;
   709		int nest_level;
   710	
   711		preempt_disable();
   712		nest_level = this_cpu_inc_return(bpf_bprintf_nest_level);
   713		if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
   714			this_cpu_dec(bpf_bprintf_nest_level);
   715			preempt_enable();
   716			return -EBUSY;
   717		}
 > 718		bufs = this_cpu_ptr(&bpf_bprintf_buf);
   719		*tmp_buf = bufs->tmp_bufs[nest_level - 1];
   720	
   721		return 0;
   722	}
   723	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Florent Revest May 11, 2021, 8:09 a.m. UTC | #3 
On Tue, May 11, 2021 at 3:58 AM kernel test robot <lkp@intel.com> wrote:
>    kernel/bpf/helpers.c:718:23: error: use of undeclared identifier 'bpf_bprintf_buf'; did you mean 'bpf_bprintf_bufs'?

Ugh, reminder to self: don't zealously rename variables just before
sending a patch out.

I'm sending a v2, sorry for the noise.
diff mbox series

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 544773970dbc..302410ebbea9 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -696,34 +696,35 @@  static int bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
  */
 #define MAX_PRINTF_BUF_LEN	512
 
-struct bpf_printf_buf {
-	char tmp_buf[MAX_PRINTF_BUF_LEN];
+/* Support executing three nested bprintf helper calls on a given CPU */
+struct bpf_bprintf_buffers {
+	char tmp_bufs[3][MAX_PRINTF_BUF_LEN];
 };
-static DEFINE_PER_CPU(struct bpf_printf_buf, bpf_printf_buf);
-static DEFINE_PER_CPU(int, bpf_printf_buf_used);
+static DEFINE_PER_CPU(struct bpf_bprintf_bufs, bpf_bprintf_bufs);
+static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
 
 static int try_get_fmt_tmp_buf(char **tmp_buf)
 {
-	struct bpf_printf_buf *bufs;
-	int used;
+	struct bpf_bprintf_buffers *bufs;
+	int nest_level;
 
 	preempt_disable();
-	used = this_cpu_inc_return(bpf_printf_buf_used);
-	if (WARN_ON_ONCE(used > 1)) {
-		this_cpu_dec(bpf_printf_buf_used);
+	nest_level = this_cpu_inc_return(bpf_bprintf_nest_level);
+	if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
+		this_cpu_dec(bpf_bprintf_nest_level);
 		preempt_enable();
 		return -EBUSY;
 	}
-	bufs = this_cpu_ptr(&bpf_printf_buf);
-	*tmp_buf = bufs->tmp_buf;
+	bufs = this_cpu_ptr(&bpf_bprintf_buf);
+	*tmp_buf = bufs->tmp_bufs[nest_level - 1];
 
 	return 0;
 }
 
 void bpf_bprintf_cleanup(void)
 {
-	if (this_cpu_read(bpf_printf_buf_used)) {
-		this_cpu_dec(bpf_printf_buf_used);
+	if (this_cpu_read(bpf_bprintf_nest_level)) {
+		this_cpu_dec(bpf_bprintf_nest_level);
 		preempt_enable();
 	}
 }