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Kumar Kartikeya Dwivedi says: ==================== BPF Standard Streams This set introduces a standard output interface with two streams, namely stdout and stderr, for BPF programs. The idea is that these streams will be written to by BPF programs and the kernel, and serve as standard interfaces for informing user space of any BPF runtime violations. Users can also utilize them for printing normal messages for debugging usage, as is the case with bpf_printk() and trace pipe interface. BPF programs and the kernel can use these streams to output messages. User space can dump these messages using bpftool. The stream interface itself is implemented using a lockless list, so that we can queue messages from any context. Every printk statement into the stream leads to memory allocation. Allocation itself relies on try_alloc_pages() to construct a bespoke bump allocator to carve out elements. If this fails, we finally give up and drop the message. See commit logs for more details. Two scenarios are covered: - Deadlocks and timeouts in rqspinlock. - Timeouts for may_goto. In each we provide the stack trace and source information for the offending BPF programs. Both the C source line and the file and line numbers are printed. The output format is as follows: ERROR: AA or ABBA deadlock detected for bpf_res_spin_lock Attempted lock = 0xff11000108f3a5e0 Total held locks = 1 Held lock[ 0] = 0xff11000108f3a5e0 CPU: 48 UID: 0 PID: 786 Comm: test_progs Call trace: bpf_stream_stage_dump_stack+0xb0/0xd0 bpf_prog_report_rqspinlock_violation+0x10b/0x130 bpf_res_spin_lock+0x8c/0xa0 bpf_prog_3699ea119d1f6ed8_foo+0xe5/0x140 if (!bpf_res_spin_lock(&v2->lock)) @ stream_bpftool.c:62 bpf_prog_9b324ec4a1b2a5c0_stream_bpftool_dump_prog_stream+0x7e/0x2d0 foo(stream); @ stream_bpftool.c:93 bpf_prog_test_run_syscall+0x102/0x240 __sys_bpf+0xd68/0x2bf0 __x64_sys_bpf+0x1e/0x30 do_syscall_64+0x68/0x140 entry_SYSCALL_64_after_hwframe+0x76/0x7e ERROR: Timeout detected for may_goto instruction CPU: 48 UID: 0 PID: 786 Comm: test_progs Call trace: bpf_stream_stage_dump_stack+0xb0/0xd0 bpf_prog_report_may_goto_violation+0x6a/0x90 bpf_check_timed_may_goto+0x4d/0xa0 arch_bpf_timed_may_goto+0x21/0x40 bpf_prog_3699ea119d1f6ed8_foo+0x12f/0x140 while (can_loop) @ stream_bpftool.c:71 bpf_prog_9b324ec4a1b2a5c0_stream_bpftool_dump_prog_stream+0x7e/0x2d0 foo(stream); @ stream_bpftool.c:93 bpf_prog_test_run_syscall+0x102/0x240 __sys_bpf+0xd68/0x2bf0 __x64_sys_bpf+0x1e/0x30 do_syscall_64+0x68/0x140 entry_SYSCALL_64_after_hwframe+0x76/0x7e Changelog: ---------- v4 -> v5 v4: https://lore.kernel.org/bpf/20250702031737.407548-1-memxor@gmail.com * Add acks from Emil. * Address various nits. * Add extra failure tests. * Make deadlock test a little more robust to catch problems. v3 -> v4 v3: https://lore.kernel.org/bpf/20250624031252.2966759-1-memxor@gmail.com * Switch to alloc_pages_nolock(), avoid incorrect memcg accounting. (Alexei) * We will figure out proper accounting later. * Drop error limit logic, restrict stream capacity to 100,000 bytes. (Alexei) * Remove extra invocation of is_bpf_text_address(). (Jiri) * Avoid emitting NULL byte into the stream text, adjust regex in selftests. (Alexei) * Add comment around rcu_read_lock() for bpf_prog_ksym_find. (Alexei) * Tighten stream capacity check selftest. * Add acks from Andrii. v2 -> v3 v2: https://lore.kernel.org/bpf/20250524011849.681425-1-memxor@gmail.com * Fix bug when handling single element stream stage. (Eduard) * Move to mutex for protection of stream read and copy_to_user(). (Alexei) * Split bprintf refactor into its own patch. (Alexei) * Move kfunc definition to common_btf_ids to avoid initcall proliferation. (Alexei) * Return line number by reference in bpf_prog_get_file_line. (Alexei) * Remove NULL checks for BTF name pointer. (Alexei) * Add WARN_ON_ONCE(!rcu_read_lock_held()) in bpf_prog_ksym_find. (Eduard) * Remove hardcoded stream stage from macros. (Alexei, Eduard) * Move refactoring hunks to their own patch. (Alexei) * Add empty opts parameter for future extensibility to libbpf API. (Andrii, Eduard) * Add BPF_STREAM_{STDOUT,STDERR} to UAPI. (Andrii) * Add code to match on backtrace output. (Eduard) * Fix misc nits. * Add acks. v1 -> v2 v1: https://lore.kernel.org/bpf/20250507171720.1958296-1-memxor@gmail.com * Drop arena page fault prints, will be done as follow up. (Alexei) * Defer Andrii's request to reuse code and Alan's suggestion of error counts to follow up. * Drop bpf_dynptr_from_mem_slice patch. * Drop some acks due to heavy reworking. * Fix KASAN splat in bpf_prog_get_file_line. (Eduard) * Collapse bpf_prog_ksym_find and is_bpf_text_address into single call. (Eduard) * Add missing RCU read lock in bpf_prog_ksym_find. * Fix incorrect error handling in dump_stack_cb. * Simplify libbpf macro. (Eduard, Andrii) * Introduce bpf_prog_stream_read() libbpf API. (Eduard, Alexei, Andrii) * Drop BPF prog from the bpftool, use libbpf API. * Rework selftests. RFC v1 -> v1 RFC v1: https://lore.kernel.org/bpf/20250414161443.1146103-1-memxor@gmail.com * Rebase on bpf-next/master. * Change output in dump_stack to also print source line. (Alexei) * Simplify API to single pop() operation. (Eduard, Alexei) * Add kdoc for bpf_dynptr_from_mem_slice. * Fix -EINVAL returned from prog_dump_stream. (Eduard) * Split dump_stack() patch into multiple commits. * Add macro wrapping stream staging API. * Change bpftool command from dump to tracelog. (Quentin) * Add bpftool documentation and bash completion. (Quentin) * Change license of bpftool to Dual BSD/GPL. * Simplify memory allocator. (Alexei) * No overflow into second page. * Remove bpf_mem_alloc() fallback. * Symlink bpftool BPF program and exercise as selftest. (Eduard) * Verify output after dumping from ringbuf. (Eduard) * More failure cases to check API invariants. * Remove patches for dynptr lifetime fixes (split into separate set). * Limit maximum error messages, and add stream capacity. (Eduard) ==================== Link: https://patch.msgid.link/20250703204818.925464-1-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.