June 2024 - Linux-kselftest-mirror

[PATCH v2 0/2] selftests/openat2, fchmodat2: fix clang build failures

by John Hubbard

These two subsystems require very similar fixes, so I'm sending them out together. Changes since the first version: 1) Rebased onto Linux 6.10-rc1. 2) Added a Reviewed-by tag from Ryan Roberts. See [1] for that. Related work: I've sent a separate fix that allows "make CC=clang" to work in addition to "make LLVM=1" [2]. [1] https://lore.kernel.org/518dd1e3-e31a-41c3-b488-9b75a64b6c8a@arm.com [2] https://lore.kernel.org/20240531183751.100541-2-jhubbard@nvidia.com John Hubbard (2): selftests/openat2: fix clang build failures: -static-libasan, LOCAL_HDRS selftests/fchmodat2: fix clang build failure due to -static-libasan tools/testing/selftests/fchmodat2/Makefile | 11 ++++++++++- tools/testing/selftests/openat2/Makefile | 14 ++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-) base-commit: cc8ed4d0a8486c7472cd72ec3c19957e509dc68c -- 2.45.1

6 months, 2 weeks

3
6
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[PATCH] selftests/sched: fix code format issues

by aigourensheng

There are extra spaces in the middle of #define. It is recommended to delete the spaces to make the code look more comfortable. Signed-off-by: aigourensheng <shechenglong001(a)gmail.com> --- tools/testing/selftests/sched/cs_prctl_test.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/tools/testing/selftests/sched/cs_prctl_test.c b/tools/testing/selftests/sched/cs_prctl_test.c index 62fba7356af2..52d97fae4dbd 100644 --- a/tools/testing/selftests/sched/cs_prctl_test.c +++ b/tools/testing/selftests/sched/cs_prctl_test.c @@ -42,11 +42,11 @@ static pid_t gettid(void) #ifndef PR_SCHED_CORE #define PR_SCHED_CORE 62 -# define PR_SCHED_CORE_GET 0 -# define PR_SCHED_CORE_CREATE 1 /* create unique core_sched cookie */ -# define PR_SCHED_CORE_SHARE_TO 2 /* push core_sched cookie to pid */ -# define PR_SCHED_CORE_SHARE_FROM 3 /* pull core_sched cookie to pid */ -# define PR_SCHED_CORE_MAX 4 +#define PR_SCHED_CORE_GET 0 +#define PR_SCHED_CORE_CREATE 1 /* create unique core_sched cookie */ +#define PR_SCHED_CORE_SHARE_TO 2 /* push core_sched cookie to pid */ +#define PR_SCHED_CORE_SHARE_FROM 3 /* pull core_sched cookie to pid */ +#define PR_SCHED_CORE_MAX 4 #endif #define MAX_PROCESSES 128 -- 2.17.1

6 months, 2 weeks

2
1
0 0

[PATCH bpf-next v3 00/11] Add check for bpf lsm return value

by Xu Kuohai

From: Xu Kuohai <xukuohai(a)huawei.com> A bpf prog returning positive number attached to file_alloc_security hook will make kernel panic. Here is a panic log: [ 441.235774] BUG: kernel NULL pointer dereference, address: 00000000000009 [ 441.236748] #PF: supervisor write access in kernel mode [ 441.237429] #PF: error_code(0x0002) - not-present page [ 441.238119] PGD 800000000b02f067 P4D 800000000b02f067 PUD b031067 PMD 0 [ 441.238990] Oops: 0002 [#1] PREEMPT SMP PTI [ 441.239546] CPU: 0 PID: 347 Comm: loader Not tainted 6.8.0-rc6-gafe0cbf23373 #22 [ 441.240496] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b4 [ 441.241933] RIP: 0010:alloc_file+0x4b/0x190 [ 441.242485] Code: 8b 04 25 c0 3c 1f 00 48 8b b0 30 0c 00 00 e8 9c fe ff ff 48 3d 00 f0 ff fb [ 441.244820] RSP: 0018:ffffc90000c67c40 EFLAGS: 00010203 [ 441.245484] RAX: ffff888006a891a0 RBX: ffffffff8223bd00 RCX: 0000000035b08000 [ 441.246391] RDX: ffff88800b95f7b0 RSI: 00000000001fc110 RDI: f089cd0b8088ffff [ 441.247294] RBP: ffffc90000c67c58 R08: 0000000000000001 R09: 0000000000000001 [ 441.248209] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000001 [ 441.249108] R13: ffffc90000c67c78 R14: ffffffff8223bd00 R15: fffffffffffffff4 [ 441.250007] FS: 00000000005f3300(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000 [ 441.251053] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 441.251788] CR2: 00000000000001a9 CR3: 000000000bdc4003 CR4: 0000000000170ef0 [ 441.252688] Call Trace: [ 441.253011] <TASK> [ 441.253296] ? __die+0x24/0x70 [ 441.253702] ? page_fault_oops+0x15b/0x480 [ 441.254236] ? fixup_exception+0x26/0x330 [ 441.254750] ? exc_page_fault+0x6d/0x1c0 [ 441.255257] ? asm_exc_page_fault+0x26/0x30 [ 441.255792] ? alloc_file+0x4b/0x190 [ 441.256257] alloc_file_pseudo+0x9f/0xf0 [ 441.256760] __anon_inode_getfile+0x87/0x190 [ 441.257311] ? lock_release+0x14e/0x3f0 [ 441.257808] bpf_link_prime+0xe8/0x1d0 [ 441.258315] bpf_tracing_prog_attach+0x311/0x570 [ 441.258916] ? __pfx_bpf_lsm_file_alloc_security+0x10/0x10 [ 441.259605] __sys_bpf+0x1bb7/0x2dc0 [ 441.260070] __x64_sys_bpf+0x20/0x30 [ 441.260533] do_syscall_64+0x72/0x140 [ 441.261004] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 441.261643] RIP: 0033:0x4b0349 [ 441.262045] Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 88 [ 441.264355] RSP: 002b:00007fff74daee38 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 [ 441.265293] RAX: ffffffffffffffda RBX: 00007fff74daef30 RCX: 00000000004b0349 [ 441.266187] RDX: 0000000000000040 RSI: 00007fff74daee50 RDI: 000000000000001c [ 441.267114] RBP: 000000000000001b R08: 00000000005ef820 R09: 0000000000000000 [ 441.268018] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004 [ 441.268907] R13: 0000000000000004 R14: 00000000005ef018 R15: 00000000004004e8 The reason is that the positive number returned by bpf prog is not a valid errno, and could not be filtered out with IS_ERR which is used by the file system to check errors. As a result, the filesystem mistakenly uses this random positive number as file pointer, causing panic. To fix this issue, there are two schemes: 1. Modify the calling sites of file_alloc_security to take positive return values as zero. 2. Make the bpf verifier to ensure no unpredicted value returned by lsm bpf prog. Considering that hook file_alloc_security never returned positive number before bpf lsm was introduced, and other lsm hooks may have the same problem, scheme 2 is more reasonable. So this series adds lsm return value check in verifier to fix it. v3: 1. Fix incorrect lsm hook return value ranges, and add disabled hook list for bpf lsm, and merge two LSM_RET_INT patches. (KP Singh) 2. Avoid bpf lsm progs attached to different hooks to call each other with tail call 3. Fix a CI failure caused by false rejection of AND operation 4. Add tests v2: https://lore.kernel.org/bpf/20240325095653.1720123-1-xukuohai@huaweicloud.c… fix bpf ci failure v1: https://lore.kernel.org/bpf/20240316122359.1073787-1-xukuohai@huaweicloud.c… Xu Kuohai (11): bpf, lsm: Annotate lsm hook return value range bpf, lsm: Add helper to read lsm hook return value range bpf, lsm: Check bpf lsm hook return values in verifier bpf, lsm: Add bpf lsm disabled hook list bpf: Avoid progs for different hooks calling each other with tail call bpf: Fix compare error in function retval_range_within bpf: Fix a false rejection caused by AND operation selftests/bpf: Avoid load failure for token_lsm.c selftests/bpf: Add return value checks for failed tests selftests/bpf: Add test for lsm tail call selftests/bpf: Add verifier tests for bpf lsm include/linux/bpf.h | 2 + include/linux/bpf_lsm.h | 8 + include/linux/lsm_hook_defs.h | 591 +++++++++--------- include/linux/lsm_hooks.h | 6 - kernel/bpf/bpf_lsm.c | 84 ++- kernel/bpf/btf.c | 5 +- kernel/bpf/core.c | 22 +- kernel/bpf/verifier.c | 82 ++- security/security.c | 1 + .../selftests/bpf/prog_tests/test_lsm.c | 46 +- .../selftests/bpf/prog_tests/verifier.c | 3 +- tools/testing/selftests/bpf/progs/err.h | 10 + .../selftests/bpf/progs/lsm_tailcall.c | 34 + .../selftests/bpf/progs/test_sig_in_xattr.c | 4 + .../bpf/progs/test_verify_pkcs7_sig.c | 8 +- tools/testing/selftests/bpf/progs/token_lsm.c | 4 +- .../bpf/progs/verifier_global_subprogs.c | 7 +- .../selftests/bpf/progs/verifier_lsm.c | 155 +++++ 18 files changed, 754 insertions(+), 318 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/lsm_tailcall.c create mode 100644 tools/testing/selftests/bpf/progs/verifier_lsm.c -- 2.30.2

6 months, 2 weeks

8
37
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[PATCH v1 0/3] Userspace controls soft-offline HugeTLB pages

by Jiaqi Yan

Correctable memory errors are very common on servers with large amount of memory, and are corrected by ECC, but with two pain points to users: 1. Correction usually happens on the fly and adds latency overhead 2. Not-fully-proved theory states excessive correctable memory errors can develop into uncorrectable memory error. Soft offline is kernel's additional solution for memory pages having (excessive) corrected memory errors. Impacted page is migrated to healthy page if it is in use, then the original page is discarded for any future use. The actual policy on whether (and when) to soft offline should be maintained by userspace, especially in case of HugeTLB hugepages. Soft-offline dissolves a hugepage, either in-use or free, into chunks of 4K pages, reducing HugeTLB pool capacity by 1 hugepage. If userspace has not acknowledged such behavior, it may be surprised when later mmap hugepages MAP_FAILED due to lack of hugepages. In addition, discarding the entire 1G memory page only because of corrected memory errors sounds very costly and kernel better not doing under the hood. But today there are at least 2 such cases: 1. GHES driver sees both GHES_SEV_CORRECTED and CPER_SEC_ERROR_THRESHOLD_EXCEEDED after parsing CPER. 2. RAS Correctable Errors Collector counts correctable errors per PFN and when the counter for a PFN reaches threshold In both cases, userspace has no control of the soft offline performed by kernel's memory failure recovery. This patch series give userspace the control of soft-offlining HugeTLB pages: kernel only soft offlines hugepage if userspace has opt-ed in for that specific hugepage size, and exposed to userspace by a new sysfs entry called softoffline_corrected_errors under /sys/kernel/mm/hugepages/hugepages-${size}kB directory: * When softoffline_corrected_errors=0, skip soft offlining for all hugepages of size ${size}kB. * When softoffline_corrected_errors=1, soft offline as before this patch series. By default softoffline_corrected_errors is 1. This patch set is based at commit a52b4f11a2e1 ("selftest mm/mseal read-only elf memory segment"). Jiaqi Yan (3): mm/memory-failure: userspace controls soft-offlining hugetlb pages selftest/mm: test softoffline_corrected_errors behaviors docs: hugetlbpage.rst: add softoffline_corrected_errors Documentation/admin-guide/mm/hugetlbpage.rst | 15 +- include/linux/hugetlb.h | 17 ++ mm/hugetlb.c | 34 +++ mm/memory-failure.c | 7 + tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + .../selftests/mm/hugetlb-soft-offline.c | 262 ++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 4 + 8 files changed, 340 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/mm/hugetlb-soft-offline.c -- 2.45.1.288.g0e0cd299f1-goog

6 months, 2 weeks

3
10
0 0

[PATCH 00/13] riscv: Add support for xtheadvector

by Charlie Jenkins

xtheadvector is a custom extension that is based upon riscv vector version 0.7.1 [1]. All of the vector routines have been modified to support this alternative vector version based upon whether xtheadvector was determined to be supported at boot. vlenb is not supported on the existing xtheadvector hardware, so a devicetree property thead,vlenb is added to provide the vlenb to Linux. There is a new hwprobe key RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0 that is used to request which thead vendor extensions are supported on the current platform. This allows future vendors to allocate hwprobe keys for their vendor. Support for xtheadvector is also added to the vector kselftests. Signed-off-by: Charlie Jenkins <charlie(a)rivosinc.com> [1] https://github.com/T-head-Semi/thead-extension-spec/blob/95358cb2cca9489361… --- This series is a continuation of a different series that was fragmented into two other series in an attempt to get part of it merged in the 6.10 merge window. The split-off series did not get merged due to a NAK on the series that added the generic riscv,vlenb devicetree entry. This series has converted riscv,vlenb to thead,vlenb to remedy this issue. The original series is titled "riscv: Support vendor extensions and xtheadvector" [3]. The series titled "riscv: Extend cpufeature.c to detect vendor extensions" is still under development and this series is based on that series! [4] I have tested this with an Allwinner Nezha board. I ran into issues booting the board after 6.9-rc1 so I applied these patches to 6.8. There are a couple of minor merge conflicts that do arrise when doing that, so please let me know if you have been able to boot this board with a 6.9 kernel. I used SkiffOS [1] to manage building the image, but upgraded the U-Boot version to Samuel Holland's more up-to-date version [2] and changed out the device tree used by U-Boot with the device trees that are present in upstream linux and this series. Thank you Samuel for all of the work you did to make this task possible. [1] https://github.com/skiffos/SkiffOS/tree/master/configs/allwinner/nezha [2] https://github.com/smaeul/u-boot/commit/2e89b706f5c956a70c989cd31665f1429e9… [3] https://lore.kernel.org/all/20240503-dev-charlie-support_thead_vector_6_9-v… [4] https://lore.kernel.org/linux-riscv/20240609-support_vendor_extensions-v2-0… --- Charlie Jenkins (12): dt-bindings: riscv: Add xtheadvector ISA extension description dt-bindings: thead: add a vlen register length property riscv: dts: allwinner: Add xtheadvector to the D1/D1s devicetree riscv: Add thead and xtheadvector as a vendor extension riscv: vector: Use vlenb from DT for thead riscv: csr: Add CSR encodings for VCSR_VXRM/VCSR_VXSAT riscv: Add xtheadvector instruction definitions riscv: vector: Support xtheadvector save/restore riscv: hwprobe: Add thead vendor extension probing riscv: hwprobe: Document thead vendor extensions and xtheadvector extension selftests: riscv: Fix vector tests selftests: riscv: Support xtheadvector in vector tests Heiko Stuebner (1): RISC-V: define the elements of the VCSR vector CSR Documentation/arch/riscv/hwprobe.rst | 10 + .../devicetree/bindings/riscv/extensions.yaml | 10 + Documentation/devicetree/bindings/riscv/thead.yaml | 7 + arch/riscv/Kconfig.vendor | 26 ++ arch/riscv/boot/dts/allwinner/sun20i-d1s.dtsi | 3 +- arch/riscv/include/asm/cpufeature.h | 2 + arch/riscv/include/asm/csr.h | 13 + arch/riscv/include/asm/hwprobe.h | 4 +- arch/riscv/include/asm/switch_to.h | 2 +- arch/riscv/include/asm/vector.h | 249 +++++++++++++---- arch/riscv/include/asm/vendor_extensions/thead.h | 42 +++ .../include/asm/vendor_extensions/thead_hwprobe.h | 18 ++ .../include/asm/vendor_extensions/vendor_hwprobe.h | 37 +++ arch/riscv/include/uapi/asm/hwprobe.h | 3 +- arch/riscv/include/uapi/asm/vendor/thead.h | 3 + arch/riscv/kernel/cpufeature.c | 51 +++- arch/riscv/kernel/kernel_mode_vector.c | 8 +- arch/riscv/kernel/process.c | 4 +- arch/riscv/kernel/signal.c | 6 +- arch/riscv/kernel/sys_hwprobe.c | 5 + arch/riscv/kernel/vector.c | 25 +- arch/riscv/kernel/vendor_extensions.c | 10 + arch/riscv/kernel/vendor_extensions/Makefile | 2 + arch/riscv/kernel/vendor_extensions/thead.c | 18 ++ .../riscv/kernel/vendor_extensions/thead_hwprobe.c | 19 ++ tools/testing/selftests/riscv/vector/.gitignore | 3 +- tools/testing/selftests/riscv/vector/Makefile | 17 +- .../selftests/riscv/vector/v_exec_initval_nolibc.c | 93 +++++++ tools/testing/selftests/riscv/vector/v_helpers.c | 67 +++++ tools/testing/selftests/riscv/vector/v_helpers.h | 7 + tools/testing/selftests/riscv/vector/v_initval.c | 22 ++ .../selftests/riscv/vector/v_initval_nolibc.c | 68 ----- .../selftests/riscv/vector/vstate_exec_nolibc.c | 20 +- .../testing/selftests/riscv/vector/vstate_prctl.c | 295 ++++++++++++--------- 34 files changed, 898 insertions(+), 271 deletions(-) --- base-commit: 11cc01d4d2af304b7288251aad7e03315db8dffc change-id: 20240530-xtheadvector-833d3d17b423 -- - Charlie

6 months, 2 weeks

6
25
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[PATCH] selftests: filesystems: add return value checks

by Abhinav Jain

Add ksft_exit_fail_msg() return value checks for fchdir() & chroot() to address the selftests statmount test compile warnings statmount_test.c:127:2: warning: ignoring return value of ‘fchdir’, declared with attribute warn_unused_result [-Wunused-result] 127 | fchdir(orig_root); | ^~~~~~~~~~~~~~~~~ statmount_test.c:128:2: warning: ignoring return value of ‘chroot’, declared with attribute warn_unused_result [-Wunused-result] 128 | chroot("."); | ^~~~~~~~~~~ Signed-off-by: Abhinav Jain <jain.abhinav177(a)gmail.com> --- .../filesystems/statmount/statmount_test.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c index e6d7c4f1c85b..b5e1247233b6 100644 --- a/tools/testing/selftests/filesystems/statmount/statmount_test.c +++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c @@ -125,8 +125,17 @@ static uint32_t old_root_id, old_parent_id; static void cleanup_namespace(void) { - fchdir(orig_root); - chroot("."); + int ret; + + ret = fchdir(orig_root); + if (ret == -1) + ksft_exit_fail_msg("changing current directory: %s\n", + strerror(errno)); + + ret = chroot("."); + if (ret == -1) + ksft_exit_fail_msg("chroot: %s\n", strerror(errno)); + umount2(root_mntpoint, MNT_DETACH); rmdir(root_mntpoint); } -- 2.34.1

6 months, 2 weeks

2
1
0 0

[PATCH] selftests: filesystems: fix warn_unused_result build warnings

by Amer Al Shanawany

Fix the following warnings by adding return check and error messages. statmount_test.c: In function ‘cleanup_namespace’: statmount_test.c:128:9: warning: ignoring return value of ‘fchdir’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 128 | fchdir(orig_root); | ^~~~~~~~~~~~~~~~~ statmount_test.c:129:9: warning: ignoring return value of ‘chroot’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 129 | chroot("."); | ^~~~~~~~~~~ Signed-off-by: Amer Al Shanawany <amer.shanawany(a)gmail.com> --- .../selftests/filesystems/statmount/statmount_test.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c index e6d7c4f1c85b..e8c019d72cbf 100644 --- a/tools/testing/selftests/filesystems/statmount/statmount_test.c +++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c @@ -125,8 +125,16 @@ static uint32_t old_root_id, old_parent_id; static void cleanup_namespace(void) { - fchdir(orig_root); - chroot("."); + int ret; + + ret = fchdir(orig_root); + if (ret == -1) + ksft_perror("fchdir to original root"); + + ret = chroot("."); + if (ret == -1) + ksft_perror("chroot to original root"); + umount2(root_mntpoint, MNT_DETACH); rmdir(root_mntpoint); } -- 2.34.1

6 months, 2 weeks

3
4
0 0

[PATCH] selftests: proc: remove unreached code and fix build warning

by Amer Al Shanawany

fix the following warning: proc-empty-vm.c:385:17: warning: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 385 | write(1, buf, rv); | ^~~~~~~~~~~~~~~~~ Reported-by: kernel test robot <lkp(a)intel.com> Closes: https://lore.kernel.org/r/202404010211.ygidvMwa-lkp@intel.com/ Signed-off-by: Amer Al Shanawany <amer.shanawany(a)gmail.com> --- tools/testing/selftests/proc/proc-empty-vm.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/tools/testing/selftests/proc/proc-empty-vm.c b/tools/testing/selftests/proc/proc-empty-vm.c index 56198d4ca2bf..b3f898aab4ab 100644 --- a/tools/testing/selftests/proc/proc-empty-vm.c +++ b/tools/testing/selftests/proc/proc-empty-vm.c @@ -381,9 +381,6 @@ static int test_proc_pid_statm(pid_t pid) assert(rv >= 0); assert(rv <= sizeof(buf)); - if (0) { - write(1, buf, rv); - } const char *p = buf; const char *const end = p + rv; -- 2.43.0

6 months, 2 weeks

4
4
0 0

[PATCH 0/5] Reorganize string-stream and assert tests

by Ivan Orlov

Currently, we can run string-stream and assertion tests only when they are built into the kernel (with config options = y), since some of the symbols (string-stream functions and functions from assert.c) are not exported into any of the namespaces, therefore they are not accessible for the modules. This patch series exports the required symbols into the KUnit namespace. Also, it makes the string-stream test a separate module and removes the log test stub from kunit-test since now we can access the string-stream symbols even if the test which uses it is built as a module. Additionally, this patch series merges the assertion test suite into the kunit-test, since assert.c (and all of the assertion formatting functions in it) is a part of the KUnit core. Ivan Orlov (5): kunit: string-stream: export non-static functions kunit: kunit-test: Remove stub for log tests kunit: string-stream-test: Make it a separate module kunit: assert: export non-static functions kunit: Merge assertion test into kunit-test.c lib/kunit/Kconfig | 8 + lib/kunit/Makefile | 7 +- lib/kunit/assert.c | 4 + lib/kunit/assert_test.c | 388 -------------------------------- lib/kunit/kunit-test.c | 397 +++++++++++++++++++++++++++++++-- lib/kunit/string-stream-test.c | 2 + lib/kunit/string-stream.c | 12 +- 7 files changed, 405 insertions(+), 413 deletions(-) delete mode 100644 lib/kunit/assert_test.c -- 2.34.1

6 months, 2 weeks

2
13
0 0

[PATCH v4 00/10] Add support for synchronous signals on perf events

by Marco Elver

The perf subsystem today unifies various tracing and monitoring features, from both software and hardware. One benefit of the perf subsystem is automatically inheriting events to child tasks, which enables process-wide events monitoring with low overheads. By default perf events are non-intrusive, not affecting behaviour of the tasks being monitored. For certain use-cases, however, it makes sense to leverage the generality of the perf events subsystem and optionally allow the tasks being monitored to receive signals on events they are interested in. This patch series adds the option to synchronously signal user space on events. To better support process-wide synchronous self-monitoring, without events propagating to children that do not share the current process's shared environment, two pre-requisite patches are added to optionally restrict inheritance to CLONE_THREAD, and remove events on exec (without affecting the parent). Examples how to use these features can be found in the tests added at the end of the series. In addition to the tests added, the series has also been subjected to syzkaller fuzzing (focus on 'kernel/events/' coverage). Motivation and Example Uses --------------------------- 1. Our immediate motivation is low-overhead sampling-based race detection for user space [1]. By using perf_event_open() at process initialization, we can create hardware breakpoint/watchpoint events that are propagated automatically to all threads in a process. As far as we are aware, today no existing kernel facility (such as ptrace) allows us to set up process-wide watchpoints with minimal overheads (that are comparable to mprotect() of whole pages). 2. Other low-overhead error detectors that rely on detecting accesses to certain memory locations or code, process-wide and also only in a specific set of subtasks or threads. [1] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf Other ideas for use-cases we found interesting, but should only illustrate the range of potential to further motivate the utility (we're sure there are more): 3. Code hot patching without full stop-the-world. Specifically, by setting a code breakpoint to entry to the patched routine, then send signals to threads and check that they are not in the routine, but without stopping them further. If any of the threads will enter the routine, it will receive SIGTRAP and pause. 4. Safepoints without mprotect(). Some Java implementations use "load from a known memory location" as a safepoint. When threads need to be stopped, the page containing the location is mprotect()ed and threads get a signal. This could be replaced with a watchpoint, which does not require a whole page nor DTLB shootdowns. 5. Threads receiving signals on performance events to throttle/unthrottle themselves. 6. Tracking data flow globally. Changelog --------- v4: * Fix for parent and child racing to exit in sync_child_event(). * Fix race between irq_work running and task's sighand being released by release_task(). * Generalize setting si_perf and si_addr independent of event type; introduces perf_event_attr::sig_data, which can be set by user space to be propagated to si_perf. * Warning in perf_sigtrap() if ctx->task and current mismatch; we expect this on architectures that do not properly implement arch_irq_work_raise(). * Require events that want sigtrap to be associated with a task. * Dropped "perf: Add breakpoint information to siginfo on SIGTRAP" in favor of more generic solution (perf_event_attr::sig_data). v3: * Add patch "perf: Rework perf_event_exit_event()" to beginning of series, courtesy of Peter Zijlstra. * Rework "perf: Add support for event removal on exec" based on the added "perf: Rework perf_event_exit_event()". * Fix kselftests to work with more recent libc, due to the way it forces using the kernel's own siginfo_t. * Add basic perf-tool built-in test. v2/RFC: https://lkml.kernel.org/r/20210310104139.679618-1-elver@google.com * Patch "Support only inheriting events if cloned with CLONE_THREAD" added to series. * Patch "Add support for event removal on exec" added to series. * Patch "Add kselftest for process-wide sigtrap handling" added to series. * Patch "Add kselftest for remove_on_exec" added to series. * Implicitly restrict inheriting events if sigtrap, but the child was cloned with CLONE_CLEAR_SIGHAND, because it is not generally safe if the child cleared all signal handlers to continue sending SIGTRAP. * Various minor fixes (see details in patches). v1/RFC: https://lkml.kernel.org/r/20210223143426.2412737-1-elver@google.com Pre-series: The discussion at [2] led to the changes in this series. The approach taken in "Add support for SIGTRAP on perf events" to trigger the signal was suggested by Peter Zijlstra in [3]. [2] https://lore.kernel.org/lkml/CACT4Y+YPrXGw+AtESxAgPyZ84TYkNZdP0xpocX2jwVAbZ… [3] https://lore.kernel.org/lkml/YBv3rAT566k+6zjg@hirez.programming.kicks-ass.n… Marco Elver (9): perf: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children perf: Support only inheriting events if cloned with CLONE_THREAD perf: Add support for event removal on exec signal: Introduce TRAP_PERF si_code and si_perf to siginfo perf: Add support for SIGTRAP on perf events selftests/perf_events: Add kselftest for process-wide sigtrap handling selftests/perf_events: Add kselftest for remove_on_exec tools headers uapi: Sync tools/include/uapi/linux/perf_event.h perf test: Add basic stress test for sigtrap handling Peter Zijlstra (1): perf: Rework perf_event_exit_event() arch/m68k/kernel/signal.c | 3 + arch/x86/kernel/signal_compat.c | 5 +- fs/signalfd.c | 4 + include/linux/compat.h | 2 + include/linux/perf_event.h | 9 +- include/linux/signal.h | 1 + include/uapi/asm-generic/siginfo.h | 6 +- include/uapi/linux/perf_event.h | 12 +- include/uapi/linux/signalfd.h | 4 +- kernel/events/core.c | 302 +++++++++++++----- kernel/fork.c | 2 +- kernel/signal.c | 11 + tools/include/uapi/linux/perf_event.h | 12 +- tools/perf/tests/Build | 1 + tools/perf/tests/builtin-test.c | 5 + tools/perf/tests/sigtrap.c | 150 +++++++++ tools/perf/tests/tests.h | 1 + .../testing/selftests/perf_events/.gitignore | 3 + tools/testing/selftests/perf_events/Makefile | 6 + tools/testing/selftests/perf_events/config | 1 + .../selftests/perf_events/remove_on_exec.c | 260 +++++++++++++++ tools/testing/selftests/perf_events/settings | 1 + .../selftests/perf_events/sigtrap_threads.c | 210 ++++++++++++ 23 files changed, 924 insertions(+), 87 deletions(-) create mode 100644 tools/perf/tests/sigtrap.c create mode 100644 tools/testing/selftests/perf_events/.gitignore create mode 100644 tools/testing/selftests/perf_events/Makefile create mode 100644 tools/testing/selftests/perf_events/config create mode 100644 tools/testing/selftests/perf_events/remove_on_exec.c create mode 100644 tools/testing/selftests/perf_events/settings create mode 100644 tools/testing/selftests/perf_events/sigtrap_threads.c -- 2.31.0.208.g409f899ff0-goog

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