From a5bde5d8fde8a8cb28e59a672d5ddc5b9c1e7656 Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Wed, 5 Aug 2026 07:52:36 -0700 Subject: workqueue: skip the node_nr_active update for non-unbound workqueues apply_wqattrs_commit() updates node_nr_active->max unconditionally. wq->node_nr_active[] is only allocated for unbound workqueues, so guard the call before per-cpu workqueues start using this path. No functional change: only unbound workqueues reach apply_wqattrs_*() today. Signed-off-by: Breno Leitao Signed-off-by: Tejun Heo --- Documentation/dev-tools/ubsan.rst | 79 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100644 Documentation/dev-tools/ubsan.rst (limited to 'Documentation/dev-tools/ubsan.rst') diff --git a/Documentation/dev-tools/ubsan.rst b/Documentation/dev-tools/ubsan.rst new file mode 100644 index 000000000..e3591f8e9 --- /dev/null +++ b/Documentation/dev-tools/ubsan.rst @@ -0,0 +1,79 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Undefined Behavior Sanitizer - UBSAN +==================================== + +UBSAN is a runtime undefined behaviour checker. + +UBSAN uses compile-time instrumentation to catch undefined behavior (UB). +Compiler inserts code that perform certain kinds of checks before operations +that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_* +function called to print error message. + +GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and +its suboptions). GCC 5.x has more checkers implemented [2_]. + +Report example +-------------- + +:: + + ================================================================================ + UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33 + shift exponent 32 is to large for 32-bit type 'unsigned int' + CPU: 0 PID: 0 Comm: swapper Not tainted 4.4.0-rc1+ #26 + 0000000000000000 ffffffff82403cc8 ffffffff815e6cd6 0000000000000001 + ffffffff82403cf8 ffffffff82403ce0 ffffffff8163a5ed 0000000000000020 + ffffffff82403d78 ffffffff8163ac2b ffffffff815f0001 0000000000000002 + Call Trace: + [] dump_stack+0x45/0x5f + [] ubsan_epilogue+0xd/0x40 + [] __ubsan_handle_shift_out_of_bounds+0xeb/0x130 + [] ? radix_tree_gang_lookup_slot+0x51/0x150 + [] _mix_pool_bytes+0x1e6/0x480 + [] ? dmi_walk_early+0x48/0x5c + [] add_device_randomness+0x61/0x130 + [] ? dmi_save_one_device+0xaa/0xaa + [] dmi_walk_early+0x48/0x5c + [] dmi_scan_machine+0x278/0x4b4 + [] ? vprintk_default+0x1a/0x20 + [] ? early_idt_handler_array+0x120/0x120 + [] setup_arch+0x405/0xc2c + [] ? early_idt_handler_array+0x120/0x120 + [] start_kernel+0x83/0x49a + [] ? early_idt_handler_array+0x120/0x120 + [] x86_64_start_reservations+0x2a/0x2c + [] x86_64_start_kernel+0x16b/0x17a + ================================================================================ + +Usage +----- + +To enable UBSAN, configure the kernel with:: + + CONFIG_UBSAN=y + +To exclude files from being instrumented use:: + + UBSAN_SANITIZE_main.o := n + +and to exclude all targets in one directory use:: + + UBSAN_SANITIZE := n + +When disabled for all targets, specific files can be enabled using:: + + UBSAN_SANITIZE_main.o := y + +Detection of unaligned accesses controlled through the separate option - +CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support +unaligned accesses (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y). One could +still enable it in config, just note that it will produce a lot of UBSAN +reports. + +References +---------- + +.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html +.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html +.. _3: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html -- cgit v1.3.1