Pull kgdb fixes from Daniel Thompson: "The main change here is a fix for a number of unsafe interactions between kdb and the console system. The fixes are specific to kdb (pure kgdb debugging does not use the console system at all). On systems with an NMI then kdb, if it is enabled, must get messages to the user despite potentially running from some "difficult" calling contexts. These fixes avoid using the console system where we have been provided an alternative (safer) way to interact with the user and, if using the console system in unavoidable, use oops_in_progress for deadlock avoidance. These fixes also ensure kdb honours the console enable flag. Also included is a fix that wraps kgdb trap handling in an RCU read lock to avoids triggering diagnostic warnings. This is a wide lock scope but this is OK because kgdb is a stop-the-world debugger. When we stop the world we put all the CPUs into holding pens and this inhibits RCU update anyway" * tag 'kgdb-5.8-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux: kgdb: Avoid suspicious RCU usage warning kdb: Switch to use safer dbg_io_ops over console APIs kdb: Make kdb_printf() console handling more robust kdb: Check status of console prior to invoking handlers kdb: Re-factor kdb_printf() message write code
Showing the changes to kernel (2 of 6 files). Show all
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| @@ -587,6 +587,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs, · 586 unmodified lines | ||
| 587 | 587 | arch_kgdb_ops.disable_hw_break(regs); |
| 588 | 588 | |
| 589 | 589 | acquirelock: |
| 590 | + rcu_read_lock(); | |
| 590 | 591 | /* |
| 591 | 592 | * Interrupts will be restored by the 'trap return' code, except when |
| 592 | 593 | * single stepping. |
| @@ -646,6 +647,7 @@ return_normal: · 53 unmodified lines | ||
| 646 | 647 | atomic_dec(&slaves_in_kgdb); |
| 647 | 648 | dbg_touch_watchdogs(); |
| 648 | 649 | local_irq_restore(flags); |
| 650 | + rcu_read_unlock(); | |
| 649 | 651 | return 0; |
| 650 | 652 | } |
| 651 | 653 | cpu_relax(); |
| @@ -664,6 +666,7 @@ return_normal: · 12 unmodified lines | ||
| 664 | 666 | raw_spin_unlock(&dbg_master_lock); |
| 665 | 667 | dbg_touch_watchdogs(); |
| 666 | 668 | local_irq_restore(flags); |
| 669 | + rcu_read_unlock(); | |
| 667 | 670 | |
| 668 | 671 | goto acquirelock; |
| 669 | 672 | } |
| @@ -787,6 +790,7 @@ kgdb_restore: · 117 unmodified lines | ||
| 787 | 790 | raw_spin_unlock(&dbg_master_lock); |
| 788 | 791 | dbg_touch_watchdogs(); |
| 789 | 792 | local_irq_restore(flags); |
| 793 | + rcu_read_unlock(); | |
| 790 | 794 | |
| 791 | 795 | return kgdb_info[cpu].ret_state; |
| 792 | 796 | } |
| @@ -542,6 +542,44 @@ static int kdb_search_string(char *searched, char *searchfor) · 541 unmodified lines | ||
| 542 | 542 | return 0; |
| 543 | 543 | } |
| 544 | 544 | |
| 545 | +static void kdb_msg_write(const char *msg, int msg_len) | |
| 546 | +{ | |
| 547 | + struct console *c; | |
| 548 | + | |
| 549 | + if (msg_len == 0) | |
| 550 | + return; | |
| 551 | + | |
| 552 | + if (dbg_io_ops) { | |
| 553 | + const char *cp = msg; | |
| 554 | + int len = msg_len; | |
| 555 | + | |
| 556 | + while (len--) { | |
| 557 | + dbg_io_ops->write_char(*cp); | |
| 558 | + cp++; | |
| 559 | + } | |
| 560 | + } | |
| 561 | + | |
| 562 | + for_each_console(c) { | |
| 563 | + if (!(c->flags & CON_ENABLED)) | |
| 564 | + continue; | |
| 565 | + if (c == dbg_io_ops->cons) | |
| 566 | + continue; | |
| 567 | + /* | |
| 568 | + * Set oops_in_progress to encourage the console drivers to | |
| 569 | + * disregard their internal spin locks: in the current calling | |
| 570 | + * context the risk of deadlock is a bigger problem than risks | |
| 571 | + * due to re-entering the console driver. We operate directly on | |
| 572 | + * oops_in_progress rather than using bust_spinlocks() because | |
| 573 | + * the calls bust_spinlocks() makes on exit are not appropriate | |
| 574 | + * for this calling context. | |
| 575 | + */ | |
| 576 | + ++oops_in_progress; | |
| 577 | + c->write(c, msg, msg_len); | |
| 578 | + --oops_in_progress; | |
| 579 | + touch_nmi_watchdog(); | |
| 580 | + } | |
| 581 | +} | |
| 582 | + | |
| 545 | 583 | int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap) |
| 546 | 584 | { |
| 547 | 585 | int diag; |
| @@ -553,7 +591,6 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap) · 5 unmodified lines | ||
| 553 | 591 | int this_cpu, old_cpu; |
| 554 | 592 | char *cp, *cp2, *cphold = NULL, replaced_byte = ' '; |
| 555 | 593 | char *moreprompt = "more> "; |
| 556 | − struct console *c; | |
| 557 | 594 | unsigned long uninitialized_var(flags); |
| 558 | 595 | |
| 559 | 596 | /* Serialize kdb_printf if multiple cpus try to write at once. |
| @@ -687,22 +724,11 @@ kdb_printit: · 127 unmodified lines | ||
| 687 | 724 | */ |
| 688 | 725 | retlen = strlen(kdb_buffer); |
| 689 | 726 | cp = (char *) printk_skip_headers(kdb_buffer); |
| 690 | − if (!dbg_kdb_mode && kgdb_connected) { | |
| 727 | + if (!dbg_kdb_mode && kgdb_connected) | |
| 691 | 728 | gdbstub_msg_write(cp, retlen - (cp - kdb_buffer)); |
| 692 | − } else { | |
| 693 | − if (dbg_io_ops && !dbg_io_ops->is_console) { | |
| 694 | − len = retlen - (cp - kdb_buffer); | |
| 695 | − cp2 = cp; | |
| 696 | − while (len--) { | |
| 697 | − dbg_io_ops->write_char(*cp2); | |
| 698 | − cp2++; | |
| 699 | − } | |
| 700 | − } | |
| 701 | − for_each_console(c) { | |
| 702 | − c->write(c, cp, retlen - (cp - kdb_buffer)); | |
| 703 | − touch_nmi_watchdog(); | |
| 704 | − } | |
| 705 | − } | |
| 729 | + else | |
| 730 | + kdb_msg_write(cp, retlen - (cp - kdb_buffer)); | |
| 731 | + | |
| 706 | 732 | if (logging) { |
| 707 | 733 | saved_loglevel = console_loglevel; |
| 708 | 734 | console_loglevel = CONSOLE_LOGLEVEL_SILENT; |
| @@ -751,19 +777,7 @@ kdb_printit: · 42 unmodified lines | ||
| 751 | 777 | moreprompt = "more> "; |
| 752 | 778 | |
| 753 | 779 | kdb_input_flush(); |
| 754 | − | |
| 755 | − if (dbg_io_ops && !dbg_io_ops->is_console) { | |
| 756 | − len = strlen(moreprompt); | |
| 757 | − cp = moreprompt; | |
| 758 | − while (len--) { | |
| 759 | − dbg_io_ops->write_char(*cp); | |
| 760 | − cp++; | |
| 761 | − } | |
| 762 | − } | |
| 763 | − for_each_console(c) { | |
| 764 | − c->write(c, moreprompt, strlen(moreprompt)); | |
| 765 | − touch_nmi_watchdog(); | |
| 766 | − } | |
| 780 | + kdb_msg_write(moreprompt, strlen(moreprompt)); | |
| 767 | 781 | |
| 768 | 782 | if (logging) |
| 769 | 783 | printk("%s", moreprompt); |