linux-stable.git/tools/testing, branch v6.1.136 Linux kernel stable tree selftests/mincore: Allow read-ahead pages to reach the end of the file 2025-05-02T05:47:06+00:00 Qiuxu Zhuo qiuxu.zhuo@intel.com 2025-03-11T08:09:40+00:00 6c94a16ba2da9a07d63429c1ca2befeb9babc0b9 [ Upstream commit 197c1eaa7ba633a482ed7588eea6fd4aa57e08d4 ] When running the mincore_selftest on a system with an XFS file system, it failed the "check_file_mmap" test case due to the read-ahead pages reaching the end of the file. The failure log is as below: RUN global.check_file_mmap ... mincore_selftest.c:264:check_file_mmap:Expected i (1024) < vec_size (1024) mincore_selftest.c:265:check_file_mmap:Read-ahead pages reached the end of the file check_file_mmap: Test failed FAIL global.check_file_mmap This is because the read-ahead window size of the XFS file system on this machine is 4 MB, which is larger than the size from the #PF address to the end of the file. As a result, all the pages for this file are populated. blockdev --getra /dev/nvme0n1p5 8192 blockdev --getbsz /dev/nvme0n1p5 512 This issue can be fixed by extending the current FILE_SIZE 4MB to a larger number, but it will still fail if the read-ahead window size of the file system is larger enough. Additionally, in the real world, read-ahead pages reaching the end of the file can happen and is an expected behavior. Therefore, allowing read-ahead pages to reach the end of the file is a better choice for the "check_file_mmap" test case. Link: https://lore.kernel.org/r/20250311080940.21413-1-qiuxu.zhuo@intel.com Reported-by: Yi Lai <yi1.lai@intel.com> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 197c1eaa7ba633a482ed7588eea6fd4aa57e08d4 ]

When running the mincore_selftest on a system with an XFS file system, it
failed the "check_file_mmap" test case due to the read-ahead pages reaching
the end of the file. The failure log is as below:

   RUN           global.check_file_mmap ...
  mincore_selftest.c:264:check_file_mmap:Expected i (1024) < vec_size (1024)
  mincore_selftest.c:265:check_file_mmap:Read-ahead pages reached the end of the file
  check_file_mmap: Test failed
           FAIL  global.check_file_mmap

This is because the read-ahead window size of the XFS file system on this
machine is 4 MB, which is larger than the size from the #PF address to the
end of the file. As a result, all the pages for this file are populated.

  blockdev --getra /dev/nvme0n1p5
    8192
  blockdev --getbsz /dev/nvme0n1p5
    512

This issue can be fixed by extending the current FILE_SIZE 4MB to a larger
number, but it will still fail if the read-ahead window size of the file
system is larger enough. Additionally, in the real world, read-ahead pages
reaching the end of the file can happen and is an expected behavior.
Therefore, allowing read-ahead pages to reach the end of the file is a
better choice for the "check_file_mmap" test case.

Link: https://lore.kernel.org/r/20250311080940.21413-1-qiuxu.zhuo@intel.com
Reported-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests: ublk: fix test_stripe_04 2025-05-02T05:47:05+00:00 Ming Lei ming.lei@redhat.com 2025-04-04T00:18:49+00:00 9ce224eb5a9aaf68cb063bd19014b270b0ac89d3 [ Upstream commit 72070e57b0a518ec8e562a2b68fdfc796ef5c040 ] Commit 57ed58c13256 ("selftests: ublk: enable zero copy for stripe target") added test entry of test_stripe_04, but forgot to add the test script. So fix the test by adding the script file. Reported-by: Uday Shankar <ushankar@purestorage.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Uday Shankar <ushankar@purestorage.com> Link: https://lore.kernel.org/r/20250404001849.1443064-1-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 72070e57b0a518ec8e562a2b68fdfc796ef5c040 ]

Commit 57ed58c13256 ("selftests: ublk: enable zero copy for stripe target")
added test entry of test_stripe_04, but forgot to add the test script.

So fix the test by adding the script file.

Reported-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Link: https://lore.kernel.org/r/20250404001849.1443064-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/mm: generate a temporary mountpoint for cgroup filesystem 2025-05-02T05:46:53+00:00 Mark Brown broonie@kernel.org 2025-04-04T16:42:32+00:00 19cc82616b44eedeacbd149a15f44ef28656d923 [ Upstream commit 9c02223e2d9df5cb37c51aedb78f3960294e09b5 ] Currently if the filesystem for the cgroups version it wants to use is not mounted charge_reserved_hugetlb.sh and hugetlb_reparenting_test.sh tests will attempt to mount it on the hard coded path /dev/cgroup/memory, deleting that directory when the test finishes. This will fail if there is not a preexisting directory at that path, and since the directory is deleted subsequent runs of the test will fail. Instead of relying on this hard coded directory name use mktemp to generate a temporary directory to use as a mountpoint, fixing both the assumption and the disruption caused by deleting a preexisting directory. This means that if the relevant cgroup filesystem is not already mounted then we rely on having coreutils (which provides mktemp) installed. I suspect that many current users are relying on having things automounted by default, and given that the script relies on bash it's probably not an unreasonable requirement. Link: https://lkml.kernel.org/r/20250404-kselftest-mm-cgroup2-detection-v1-1-3dba6d32ba8c@kernel.org Fixes: 209376ed2a84 ("selftests/vm: make charge_reserved_hugetlb.sh work with existing cgroup setting") Signed-off-by: Mark Brown <broonie@kernel.org> Cc: Aishwarya TCV <aishwarya.tcv@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Mina Almasry <almasrymina@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 9c02223e2d9df5cb37c51aedb78f3960294e09b5 ]

Currently if the filesystem for the cgroups version it wants to use is not
mounted charge_reserved_hugetlb.sh and hugetlb_reparenting_test.sh tests
will attempt to mount it on the hard coded path /dev/cgroup/memory,
deleting that directory when the test finishes.  This will fail if there
is not a preexisting directory at that path, and since the directory is
deleted subsequent runs of the test will fail.  Instead of relying on this
hard coded directory name use mktemp to generate a temporary directory to
use as a mountpoint, fixing both the assumption and the disruption caused
by deleting a preexisting directory.

This means that if the relevant cgroup filesystem is not already mounted
then we rely on having coreutils (which provides mktemp) installed.  I
suspect that many current users are relying on having things automounted
by default, and given that the script relies on bash it's probably not an
unreasonable requirement.

Link: https://lkml.kernel.org/r/20250404-kselftest-mm-cgroup2-detection-v1-1-3dba6d32ba8c@kernel.org
Fixes: 209376ed2a84 ("selftests/vm: make charge_reserved_hugetlb.sh work with existing cgroup setting")
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Aishwarya TCV <aishwarya.tcv@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
landlock: Add the errata interface 2025-04-25T08:44:02+00:00 Mickaël Salaün mic@digikod.net 2025-03-18T16:14:37+00:00 b66bc16f4c1bcdd7d6d9fa6fa0c43544720b858a commit 15383a0d63dbcd63dc7e8d9ec1bf3a0f7ebf64ac upstream. Some fixes may require user space to check if they are applied on the running kernel before using a specific feature. For instance, this applies when a restriction was previously too restrictive and is now getting relaxed (e.g. for compatibility reasons). However, non-visible changes for legitimate use (e.g. security fixes) do not require an erratum. Because fixes are backported down to a specific Landlock ABI, we need a way to avoid cherry-pick conflicts. The solution is to only update a file related to the lower ABI impacted by this issue. All the ABI files are then used to create a bitmask of fixes. The new errata interface is similar to the one used to get the supported Landlock ABI version, but it returns a bitmask instead because the order of fixes may not match the order of versions, and not all fixes may apply to all versions. The actual errata will come with dedicated commits. The description is not actually used in the code but serves as documentation. Create the landlock_abi_version symbol and use its value to check errata consistency. Update test_base's create_ruleset_checks_ordering tests and add errata tests. This commit is backportable down to the first version of Landlock. Fixes: 3532b0b4352c ("landlock: Enable user space to infer supported features") Cc: Günther Noack <gnoack@google.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250318161443.279194-3-mic@digikod.net Signed-off-by: Mickaël Salaün <mic@digikod.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 15383a0d63dbcd63dc7e8d9ec1bf3a0f7ebf64ac upstream.

Some fixes may require user space to check if they are applied on the
running kernel before using a specific feature.  For instance, this
applies when a restriction was previously too restrictive and is now
getting relaxed (e.g. for compatibility reasons).  However, non-visible
changes for legitimate use (e.g. security fixes) do not require an
erratum.

Because fixes are backported down to a specific Landlock ABI, we need a
way to avoid cherry-pick conflicts.  The solution is to only update a
file related to the lower ABI impacted by this issue.  All the ABI files
are then used to create a bitmask of fixes.

The new errata interface is similar to the one used to get the supported
Landlock ABI version, but it returns a bitmask instead because the order
of fixes may not match the order of versions, and not all fixes may
apply to all versions.

The actual errata will come with dedicated commits.  The description is
not actually used in the code but serves as documentation.

Create the landlock_abi_version symbol and use its value to check errata
consistency.

Update test_base's create_ruleset_checks_ordering tests and add errata
tests.

This commit is backportable down to the first version of Landlock.

Fixes: 3532b0b4352c ("landlock: Enable user space to infer supported features")
Cc: Günther Noack <gnoack@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250318161443.279194-3-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
test suite: use %zu to print size_t 2025-04-25T08:43:50+00:00 Matthew Wilcox (Oracle) willy@infradead.org 2025-04-03T00:33:11+00:00 d8a632fbc739052f33e405851389c7fff90c13f4 [ Upstream commit a30951d09c33c899f0e4aca80eb87fad5f10ecfa ] On 32-bit, we can't use %lu to print a size_t variable and gcc warns us about it. Shame it doesn't warn about it on 64-bit. Link: https://lkml.kernel.org/r/20250403003311.359917-1-Liam.Howlett@oracle.com Fixes: cc86e0c2f306 ("radix tree test suite: add support for slab bulk APIs") Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a30951d09c33c899f0e4aca80eb87fad5f10ecfa ]

On 32-bit, we can't use %lu to print a size_t variable and gcc warns us
about it.  Shame it doesn't warn about it on 64-bit.

Link: https://lkml.kernel.org/r/20250403003311.359917-1-Liam.Howlett@oracle.com
Fixes: cc86e0c2f306 ("radix tree test suite: add support for slab bulk APIs")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests: mptcp: close fd_in before returning in main_loop 2025-04-25T08:43:46+00:00 Geliang Tang tanggeliang@kylinos.cn 2025-03-28T14:27:18+00:00 47b445fc799461c76476bd9a488e12cf1113c3bb commit c183165f87a486d5879f782c05a23c179c3794ab upstream. The file descriptor 'fd_in' is opened when cfg_input is configured, but not closed in main_loop(), this patch fixes it. Fixes: 05be5e273c84 ("selftests: mptcp: add disconnect tests") Cc: stable@vger.kernel.org Co-developed-by: Cong Liu <liucong2@kylinos.cn> Signed-off-by: Cong Liu <liucong2@kylinos.cn> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn> Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Link: https://patch.msgid.link/20250328-net-mptcp-misc-fixes-6-15-v1-3-34161a482a7f@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit c183165f87a486d5879f782c05a23c179c3794ab upstream.

The file descriptor 'fd_in' is opened when cfg_input is configured, but
not closed in main_loop(), this patch fixes it.

Fixes: 05be5e273c84 ("selftests: mptcp: add disconnect tests")
Cc: stable@vger.kernel.org
Co-developed-by: Cong Liu <liucong2@kylinos.cn>
Signed-off-by: Cong Liu <liucong2@kylinos.cn>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250328-net-mptcp-misc-fixes-6-15-v1-3-34161a482a7f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ktest: Fix Test Failures Due to Missing LOG_FILE Directories 2025-04-25T08:43:34+00:00 Ayush Jain Ayush.jain3@amd.com 2025-03-07T04:38:54+00:00 1a5b71022e7210797d15a7f2cb099432901de937 [ Upstream commit 5a1bed232781d356f842576daacc260f0d0c8d2e ] Handle missing parent directories for LOG_FILE path to prevent test failures. If the parent directories don't exist, create them to ensure the tests proceed successfully. Cc: <warthog9@eaglescrag.net> Link: https://lore.kernel.org/20250307043854.2518539-1-Ayush.jain3@amd.com Signed-off-by: Ayush Jain <Ayush.jain3@amd.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 5a1bed232781d356f842576daacc260f0d0c8d2e ]

Handle missing parent directories for LOG_FILE path to prevent test
failures. If the parent directories don't exist, create them to ensure
the tests proceed successfully.

Cc: <warthog9@eaglescrag.net>
Link: https://lore.kernel.org/20250307043854.2518539-1-Ayush.jain3@amd.com
Signed-off-by: Ayush Jain <Ayush.jain3@amd.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/futex: futex_waitv wouldblock test should fail 2025-04-25T08:43:24+00:00 Edward Liaw edliaw@google.com 2025-04-04T22:12:20+00:00 d4d8662e6ec0faf4000de7f21309e0e08d49ceb1 [ Upstream commit 7d50e00fef2832e98d7e06bbfc85c1d66ee110ca ] Testcase should fail if -EWOULDBLOCK is not returned when expected value differs from actual value from the waiter. Link: https://lore.kernel.org/r/20250404221225.1596324-1-edliaw@google.com Fixes: 9d57f7c79748920636f8293d2f01192d702fe390 ("selftests: futex: Test sys_futex_waitv() wouldblock") Signed-off-by: Edward Liaw <edliaw@google.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: André Almeida <andrealmeid@igalia.com> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 7d50e00fef2832e98d7e06bbfc85c1d66ee110ca ]

Testcase should fail if -EWOULDBLOCK is not returned when expected value
differs from actual value from the waiter.

Link: https://lore.kernel.org/r/20250404221225.1596324-1-edliaw@google.com
Fixes: 9d57f7c79748920636f8293d2f01192d702fe390 ("selftests: futex: Test sys_futex_waitv() wouldblock")
Signed-off-by: Edward Liaw <edliaw@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/bpf: Select NUMA_NO_NODE to create map 2025-04-10T12:33:35+00:00 Saket Kumar Bhaskar skb99@linux.ibm.com 2025-01-31T07:05:22+00:00 99db75157985f27a2ec83cfaa7c62c813bf25ebb [ Upstream commit 4107a1aeb20ed4cdad6a0d49de92ea0f933c71b7 ] On powerpc, a CPU does not necessarily originate from NUMA node 0. This contrasts with architectures like x86, where CPU 0 is not hot-pluggable, making NUMA node 0 a consistently valid node. This discrepancy can lead to failures when creating a map on NUMA node 0, which is initialized by default, if no CPUs are allocated from NUMA node 0. This patch fixes the issue by setting NUMA_NO_NODE (-1) for map creation for this selftest. Fixes: 96eabe7a40aa ("bpf: Allow selecting numa node during map creation") Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Yonghong Song <yonghong.song@linux.dev> Link: https://lore.kernel.org/bpf/cf1f61468b47425ecf3728689bc9636ddd1d910e.1738302337.git.skb99@linux.ibm.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 4107a1aeb20ed4cdad6a0d49de92ea0f933c71b7 ]

On powerpc, a CPU does not necessarily originate from NUMA node 0.
This contrasts with architectures like x86, where CPU 0 is not
hot-pluggable, making NUMA node 0 a consistently valid node.
This discrepancy can lead to failures when creating a map on NUMA
node 0, which is initialized by default, if no CPUs are allocated
from NUMA node 0.

This patch fixes the issue by setting NUMA_NO_NODE (-1) for map
creation for this selftest.

Fixes: 96eabe7a40aa ("bpf: Allow selecting numa node during map creation")
Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/cf1f61468b47425ecf3728689bc9636ddd1d910e.1738302337.git.skb99@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
selftests/bpf: Fix string read in strncmp benchmark 2025-04-10T12:33:33+00:00 Viktor Malik vmalik@redhat.com 2025-03-13T12:28:52+00:00 54380eea1f7f3ba8f32372aa00c7e92a5e425db9 [ Upstream commit de07b182899227d5fd1ca7a1a7d495ecd453d49c ] The strncmp benchmark uses the bpf_strncmp helper and a hand-written loop to compare two strings. The values of the strings are filled from userspace. One of the strings is non-const (in .bss) while the other is const (in .rodata) since that is the requirement of bpf_strncmp. The problem is that in the hand-written loop, Clang optimizes the reads from the const string to always return 0 which breaks the benchmark. Use barrier_var to prevent the optimization. The effect can be seen on the strncmp-no-helper variant. Before this change: # ./bench strncmp-no-helper Setting up benchmark 'strncmp-no-helper'... Benchmark 'strncmp-no-helper' started. Iter 0 (112.309us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 1 (-23.238us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 2 ( 58.994us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 3 (-30.466us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 4 ( 29.996us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 5 ( 16.949us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Iter 6 (-60.035us): hits 0.000M/s ( 0.000M/prod), drops 0.000M/s, total operations 0.000M/s Summary: hits 0.000 ± 0.000M/s ( 0.000M/prod), drops 0.000 ± 0.000M/s, total operations 0.000 ± 0.000M/s After this change: # ./bench strncmp-no-helper Setting up benchmark 'strncmp-no-helper'... Benchmark 'strncmp-no-helper' started. Iter 0 ( 77.711us): hits 5.534M/s ( 5.534M/prod), drops 0.000M/s, total operations 5.534M/s Iter 1 ( 11.215us): hits 6.006M/s ( 6.006M/prod), drops 0.000M/s, total operations 6.006M/s Iter 2 (-14.253us): hits 5.931M/s ( 5.931M/prod), drops 0.000M/s, total operations 5.931M/s Iter 3 ( 59.087us): hits 6.005M/s ( 6.005M/prod), drops 0.000M/s, total operations 6.005M/s Iter 4 (-21.379us): hits 6.010M/s ( 6.010M/prod), drops 0.000M/s, total operations 6.010M/s Iter 5 (-20.310us): hits 5.861M/s ( 5.861M/prod), drops 0.000M/s, total operations 5.861M/s Iter 6 ( 53.937us): hits 6.004M/s ( 6.004M/prod), drops 0.000M/s, total operations 6.004M/s Summary: hits 5.969 ± 0.061M/s ( 5.969M/prod), drops 0.000 ± 0.000M/s, total operations 5.969 ± 0.061M/s Fixes: 9c42652f8be3 ("selftests/bpf: Add benchmark for bpf_strncmp() helper") Suggested-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Viktor Malik <vmalik@redhat.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/bpf/20250313122852.1365202-1-vmalik@redhat.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit de07b182899227d5fd1ca7a1a7d495ecd453d49c ]

The strncmp benchmark uses the bpf_strncmp helper and a hand-written
loop to compare two strings. The values of the strings are filled from
userspace. One of the strings is non-const (in .bss) while the other is
const (in .rodata) since that is the requirement of bpf_strncmp.

The problem is that in the hand-written loop, Clang optimizes the reads
from the const string to always return 0 which breaks the benchmark.

Use barrier_var to prevent the optimization.

The effect can be seen on the strncmp-no-helper variant.

Before this change:

    # ./bench strncmp-no-helper
    Setting up benchmark 'strncmp-no-helper'...
    Benchmark 'strncmp-no-helper' started.
    Iter   0 (112.309us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   1 (-23.238us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   2 ( 58.994us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   3 (-30.466us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   4 ( 29.996us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   5 ( 16.949us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Iter   6 (-60.035us): hits    0.000M/s (  0.000M/prod), drops    0.000M/s, total operations    0.000M/s
    Summary: hits    0.000 ± 0.000M/s (  0.000M/prod), drops    0.000 ± 0.000M/s, total operations    0.000 ± 0.000M/s

After this change:

    # ./bench strncmp-no-helper
    Setting up benchmark 'strncmp-no-helper'...
    Benchmark 'strncmp-no-helper' started.
    Iter   0 ( 77.711us): hits    5.534M/s (  5.534M/prod), drops    0.000M/s, total operations    5.534M/s
    Iter   1 ( 11.215us): hits    6.006M/s (  6.006M/prod), drops    0.000M/s, total operations    6.006M/s
    Iter   2 (-14.253us): hits    5.931M/s (  5.931M/prod), drops    0.000M/s, total operations    5.931M/s
    Iter   3 ( 59.087us): hits    6.005M/s (  6.005M/prod), drops    0.000M/s, total operations    6.005M/s
    Iter   4 (-21.379us): hits    6.010M/s (  6.010M/prod), drops    0.000M/s, total operations    6.010M/s
    Iter   5 (-20.310us): hits    5.861M/s (  5.861M/prod), drops    0.000M/s, total operations    5.861M/s
    Iter   6 ( 53.937us): hits    6.004M/s (  6.004M/prod), drops    0.000M/s, total operations    6.004M/s
    Summary: hits    5.969 ± 0.061M/s (  5.969M/prod), drops    0.000 ± 0.000M/s, total operations    5.969 ± 0.061M/s

Fixes: 9c42652f8be3 ("selftests/bpf: Add benchmark for bpf_strncmp() helper")
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20250313122852.1365202-1-vmalik@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>