Hello, Here is a v2 for the first series to rework the printk subsystem. The v1 and history are here [0]. This first series only replaces the existing ringbuffer implementation. No locking is removed. No semantics/behavior of printk are changed.
The VMCOREINFO is updated. RFC patches for the external tools crash(8) [1] and makedumpfile(8) [2] have been submitted that allow the new ringbuffer to be correctly read. This series is in line with the agreements [3] made at the meeting during LPC2019 in Lisbon, with 1 exception: support for dictionaries will not be discontinued [4]. Dictionaries are stored in a separate buffer so that they cannot interfere with the human-readable buffer. The list of changes since v1: printk_ringbuffer ================= - documentation formatting/wording cleanup - main memory barrier comments moved from memory accesses to memory barriers - remove all symbol exporting of printk_ringbuffer functions - add prb_count_lines() for line counting so printk.c can also use this functionality - add prb_read_valid_info() to just read record meta-data - remove @line_count out of printk_record (there is now an interface for line counting) - to_block(): remove intermediate (char *) typecast - data_alloc(): use WRITE_ONCE for writing block ID - data_push_tail(): fix test condition for tail LPOS already pushed - data_push_tail(): continue loop rather than try cmpxchg() if tail LPOS was pushed - data_push_tail(): add memory barrier before pushing tail LPOS so readers can recognize if data has expired while reading the descriptor - data_make_reusable(): added memory barrier and logic to protect against invalid read of block ID - data_alloc(): add memory barrier to guarantee the tail ID is stored before updating the block ID - desc_reserve(): add memory barrier before checking ID to make sure the head ID is read before the tail ID - desc_reserve(): move memory barrier to before the head ID is pushed to guarantee the tail ID is stored before the head ID printk.c ======== - remove static syslog_record/console_record (use dynamic allocation and in-place buffer manipulation instead) - reduce expected average message size from 64 to 32 - add printk_record initializers to simplify reader and writer code - fix wrong return value when log_store() truncates - add full VMCOREINFO needed by makedumpfile(8) - change record_print_text() to add prefix data to the buffer in-place instead of requiring a 2nd buffer - add helper to calculate text size when prefix added: get_record_text_size() (used together with prb_count_lines() or prb_read_valid_info() to get full text size, rather than abusing record_print_text() for this purpose) - syslog_print_all(): fix missing break if copy_to_user() failed - moved "messages dropped" printing to call_console_drivers() John Ogness [0] https://lkml.kernel.org/r/20200128161948.8524-1-john.ogn...@linutronix.de [1] https://www.redhat.com/archives/crash-utility/2020-April/msg00080.html [2] https://lists.infradead.org/pipermail/kexec/2020-April/024906.html [3] https://lkml.kernel.org/r/87k1acz5rx....@linutronix.de [4] https://lkml.kernel.org/r/20191007120134.ciywr3wale4gx...@pathway.suse.cz John Ogness (3): crash: add VMCOREINFO macro for anonymous structs printk: add lockless buffer printk: use the lockless ringbuffer include/linux/crash_core.h | 3 + include/linux/kmsg_dump.h | 2 - kernel/printk/Makefile | 1 + kernel/printk/printk.c | 938 +++++++++-------- kernel/printk/printk_ringbuffer.c | 1626 +++++++++++++++++++++++++++++ kernel/printk/printk_ringbuffer.h | 369 +++++++ 6 files changed, 2491 insertions(+), 448 deletions(-) create mode 100644 kernel/printk/printk_ringbuffer.c create mode 100644 kernel/printk/printk_ringbuffer.h -- 2.20.1
