From bf61ad1f870be88676a07bfef69acd59ce10172e Mon Sep 17 00:00:00 2001 From: Matt Fleming Date: Thu, 13 Aug 2009 19:49:03 +0900 Subject: sh: Allow multiple stack unwinders to be setup Provide an interface for registering stack unwinders, where each unwinder is given a rating that describes its accuracy and complexity. The more accurate an unwinder is, the more complex it is. If a the current stack unwinder faults, then the stack unwinder with the next highest accuracy will be used in its place (provided one is available). For example, this allows unwinders, such as the DWARF unwinder, to liberally sprinkle BUG()s to catch badly formed DWARF debug info. Signed-off-by: Matt Fleming Signed-off-by: Paul Mundt --- arch/sh/kernel/unwinder.c | 162 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 162 insertions(+) create mode 100644 arch/sh/kernel/unwinder.c (limited to 'arch/sh/kernel/unwinder.c') diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c new file mode 100644 index 000000000000..2b30fa28b440 --- /dev/null +++ b/arch/sh/kernel/unwinder.c @@ -0,0 +1,162 @@ +/* + * Copyright (C) 2009 Matt Fleming + * + * Based, in part, on kernel/time/clocksource.c. + * + * This file provides arbitration code for stack unwinders. + * + * Multiple stack unwinders can be available on a system, usually with + * the most accurate unwinder being the currently active one. + */ +#include +#include +#include +#include +#include + +/* + * This is the most basic stack unwinder an architecture can + * provide. For architectures without reliable frame pointers, e.g. + * RISC CPUs, it can be implemented by looking through the stack for + * addresses that lie within the kernel text section. + * + * Other CPUs, e.g. x86, can use their frame pointer register to + * construct more accurate stack traces. + */ +static struct list_head unwinder_list; +static struct unwinder stack_reader = { + .name = "stack-reader", + .dump = stack_reader_dump, + .rating = 50, + .list = { + .next = &unwinder_list, + .prev = &unwinder_list, + }, +}; + +/* + * "curr_unwinder" points to the stack unwinder currently in use. This + * is the unwinder with the highest rating. + * + * "unwinder_list" is a linked-list of all available unwinders, sorted + * by rating. + * + * All modifications of "curr_unwinder" and "unwinder_list" must be + * performed whilst holding "unwinder_lock". + */ +static struct unwinder *curr_unwinder = &stack_reader; + +static struct list_head unwinder_list = { + .next = &stack_reader.list, + .prev = &stack_reader.list, +}; + +static DEFINE_SPINLOCK(unwinder_lock); + +static atomic_t unwinder_running = ATOMIC_INIT(0); + +/** + * select_unwinder - Select the best registered stack unwinder. + * + * Private function. Must hold unwinder_lock when called. + * + * Select the stack unwinder with the best rating. This is useful for + * setting up curr_unwinder. + */ +static struct unwinder *select_unwinder(void) +{ + struct unwinder *best; + + if (list_empty(&unwinder_list)) + return NULL; + + best = list_entry(unwinder_list.next, struct unwinder, list); + if (best == curr_unwinder) + return NULL; + + return best; +} + +/* + * Enqueue the stack unwinder sorted by rating. + */ +static int unwinder_enqueue(struct unwinder *ops) +{ + struct list_head *tmp, *entry = &unwinder_list; + + list_for_each(tmp, &unwinder_list) { + struct unwinder *o; + + o = list_entry(tmp, struct unwinder, list); + if (o == ops) + return -EBUSY; + /* Keep track of the place, where to insert */ + if (o->rating >= ops->rating) + entry = tmp; + } + list_add(&ops->list, entry); + + return 0; +} + +/** + * unwinder_register - Used to install new stack unwinder + * @u: unwinder to be registered + * + * Install the new stack unwinder on the unwinder list, which is sorted + * by rating. + * + * Returns -EBUSY if registration fails, zero otherwise. + */ +int unwinder_register(struct unwinder *u) +{ + unsigned long flags; + int ret; + + spin_lock_irqsave(&unwinder_lock, flags); + ret = unwinder_enqueue(u); + if (!ret) + curr_unwinder = select_unwinder(); + spin_unlock_irqrestore(&unwinder_lock, flags); + + return ret; +} + +/* + * Unwind the call stack and pass information to the stacktrace_ops + * functions. Also handle the case where we need to switch to a new + * stack dumper because the current one faulted unexpectedly. + */ +void unwind_stack(struct task_struct *task, struct pt_regs *regs, + unsigned long *sp, const struct stacktrace_ops *ops, + void *data) +{ + unsigned long flags; + + /* + * The problem with unwinders with high ratings is that they are + * inherently more complicated than the simple ones with lower + * ratings. We are therefore more likely to fault in the + * complicated ones, e.g. hitting BUG()s. If we fault in the + * code for the current stack unwinder we try to downgrade to + * one with a lower rating. + * + * Hopefully this will give us a semi-reliable stacktrace so we + * can diagnose why curr_unwinder->dump() faulted. + */ + if (atomic_inc_return(&unwinder_running) != 1) { + spin_lock_irqsave(&unwinder_lock, flags); + + if (!list_is_singular(&unwinder_list)) { + list_del(&curr_unwinder->list); + curr_unwinder = select_unwinder(); + } + + spin_unlock_irqrestore(&unwinder_lock, flags); + atomic_dec(&unwinder_running); + } + + curr_unwinder->dump(task, regs, sp, ops, data); + + atomic_dec(&unwinder_running); +} -- cgit v1.2.3 From b344e24a8e8ceda83d1285d22e3e5baf4f5e42d3 Mon Sep 17 00:00:00 2001 From: Matt Fleming Date: Sun, 16 Aug 2009 21:54:48 +0100 Subject: sh: unwinder: Introduce UNWINDER_BUG() and UNWINDER_BUG_ON() We can't assume that if we execute the unwinder code and the unwinder was already running that it has faulted. Clearly two kernel threads can invoke the unwinder at the same time and may be running simultaneously. The previous approach used BUG() and BUG_ON() in the unwinder code to detect whether the unwinder was incapable of unwinding the stack, and that the next available unwinder should be used instead. A better approach is to explicitly invoke a trap handler to switch unwinders when the current unwinder cannot continue. Signed-off-by: Matt Fleming --- arch/sh/kernel/unwinder.c | 33 +++++++++++++++++++++++++++------ 1 file changed, 27 insertions(+), 6 deletions(-) (limited to 'arch/sh/kernel/unwinder.c') diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c index 2b30fa28b440..b9c122abe251 100644 --- a/arch/sh/kernel/unwinder.c +++ b/arch/sh/kernel/unwinder.c @@ -53,8 +53,6 @@ static struct list_head unwinder_list = { static DEFINE_SPINLOCK(unwinder_lock); -static atomic_t unwinder_running = ATOMIC_INIT(0); - /** * select_unwinder - Select the best registered stack unwinder. * @@ -122,6 +120,8 @@ int unwinder_register(struct unwinder *u) return ret; } +int unwinder_faulted = 0; + /* * Unwind the call stack and pass information to the stacktrace_ops * functions. Also handle the case where we need to switch to a new @@ -144,19 +144,40 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs, * Hopefully this will give us a semi-reliable stacktrace so we * can diagnose why curr_unwinder->dump() faulted. */ - if (atomic_inc_return(&unwinder_running) != 1) { + if (unwinder_faulted) { spin_lock_irqsave(&unwinder_lock, flags); - if (!list_is_singular(&unwinder_list)) { + /* Make sure no one beat us to changing the unwinder */ + if (unwinder_faulted && !list_is_singular(&unwinder_list)) { list_del(&curr_unwinder->list); curr_unwinder = select_unwinder(); + + unwinder_faulted = 0; } spin_unlock_irqrestore(&unwinder_lock, flags); - atomic_dec(&unwinder_running); } curr_unwinder->dump(task, regs, sp, ops, data); +} + +/* + * Trap handler for UWINDER_BUG() statements. We must switch to the + * unwinder with the next highest rating. + */ +BUILD_TRAP_HANDLER(unwinder) +{ + insn_size_t insn; + TRAP_HANDLER_DECL; + + /* Rewind */ + regs->pc -= instruction_size(ctrl_inw(regs->pc - 4)); + insn = *(insn_size_t *)instruction_pointer(regs); + + /* Switch unwinders when unwind_stack() is called */ + unwinder_faulted = 1; - atomic_dec(&unwinder_running); +#ifdef CONFIG_BUG + handle_BUG(regs); +#endif } -- cgit v1.2.3 From 4ab8f241f6d510470c15b62ac10f6905ff5c97bd Mon Sep 17 00:00:00 2001 From: Paul Mundt Date: Sat, 22 Aug 2009 03:43:15 +0900 Subject: sh: Export unwind_stack() to satisfy modular oprofile. If the oprofile code is built as a module, unwind_stack() as used by the oprofile backtrace code is not available, causing build breakage. Signed-off-by: Paul Mundt --- arch/sh/kernel/unwinder.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/sh/kernel/unwinder.c') diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c index 2b30fa28b440..5f56ff3f55e0 100644 --- a/arch/sh/kernel/unwinder.c +++ b/arch/sh/kernel/unwinder.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -160,3 +161,4 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs, atomic_dec(&unwinder_running); } +EXPORT_SYMBOL_GPL(unwind_stack); -- cgit v1.2.3 From e115f2c17cbceee93b34d787a7a4a867fc73e7b4 Mon Sep 17 00:00:00 2001 From: Paul Mundt Date: Sat, 22 Aug 2009 05:28:25 +0900 Subject: sh: unwinder: Use a special bug flag for unwinder traps. This simplifies the unwinder trap handling, dropping the use of the special trapa vector and simply piggybacking on top of the BUG support. A new BUGFLAG_UNWINDER is added for flagging the unwinder fault, before continuing on with regular BUG dispatch. Signed-off-by: Paul Mundt --- arch/sh/kernel/unwinder.c | 21 --------------------- 1 file changed, 21 deletions(-) (limited to 'arch/sh/kernel/unwinder.c') diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c index e83861d9739c..468889d958f4 100644 --- a/arch/sh/kernel/unwinder.c +++ b/arch/sh/kernel/unwinder.c @@ -161,25 +161,4 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs, curr_unwinder->dump(task, regs, sp, ops, data); } - -/* - * Trap handler for UWINDER_BUG() statements. We must switch to the - * unwinder with the next highest rating. - */ -BUILD_TRAP_HANDLER(unwinder) -{ - insn_size_t insn; - TRAP_HANDLER_DECL; - - /* Rewind */ - regs->pc -= instruction_size(ctrl_inw(regs->pc - 4)); - insn = *(insn_size_t *)instruction_pointer(regs); - - /* Switch unwinders when unwind_stack() is called */ - unwinder_faulted = 1; - -#ifdef CONFIG_BUG - handle_BUG(regs); -#endif -} EXPORT_SYMBOL_GPL(unwind_stack); -- cgit v1.2.3