From a25d036d939a30623ff73ecad9c8b9116b02e823 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Thu, 5 Nov 2020 21:32:45 -0500 Subject: ftrace: Reverse what the RECURSION flag means in the ftrace_ops Now that all callbacks are recursion safe, reverse the meaning of the RECURSION flag and rename it from RECURSION_SAFE to simply RECURSION. Now only callbacks that request to have recursion protecting it will have the added trampoline to do so. Also remove the outdated comment about "PER_CPU" when determining to use the ftrace_ops_assist_func. Link: https://lkml.kernel.org/r/20201028115613.742454631@goodmis.org Link: https://lkml.kernel.org/r/20201106023547.904270143@goodmis.org Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Josh Poimboeuf Cc: Jiri Kosina Cc: Masami Hiramatsu Cc: Andrew Morton Cc: Jonathan Corbet Cc: Sebastian Andrzej Siewior Cc: Miroslav Benes Cc: Kamalesh Babulal Cc: Petr Mladek Cc: linux-doc@vger.kernel.org Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/ftrace-uses.rst | 82 +++++++++++++++++++++++++++---------- 1 file changed, 60 insertions(+), 22 deletions(-) (limited to 'Documentation/trace') diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index a4955f7e3d19..86cd14b8e126 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -30,8 +30,8 @@ The ftrace context This requires extra care to what can be done inside a callback. A callback can be called outside the protective scope of RCU. -The ftrace infrastructure has some protections against recursions and RCU -but one must still be very careful how they use the callbacks. +There are helper functions to help against recursion, and making sure +RCU is watching. These are explained below. The ftrace_ops structure @@ -108,6 +108,50 @@ The prototype of the callback function is as follows (as of v4.14): at the start of the function where ftrace was tracing. Otherwise it either contains garbage, or NULL. +Protect your callback +===================== + +As functions can be called from anywhere, and it is possible that a function +called by a callback may also be traced, and call that same callback, +recursion protection must be used. There are two helper functions that +can help in this regard. If you start your code with: + + int bit; + + bit = ftrace_test_recursion_trylock(); + if (bit < 0) + return; + +and end it with: + + ftrace_test_recursion_unlock(bit); + +The code in between will be safe to use, even if it ends up calling a +function that the callback is tracing. Note, on success, +ftrace_test_recursion_trylock() will disable preemption, and the +ftrace_test_recursion_unlock() will enable it again (if it was previously +enabled). + +Alternatively, if the FTRACE_OPS_FL_RECURSION flag is set on the ftrace_ops +(as explained below), then a helper trampoline will be used to test +for recursion for the callback and no recursion test needs to be done. +But this is at the expense of a slightly more overhead from an extra +function call. + +If your callback accesses any data or critical section that requires RCU +protection, it is best to make sure that RCU is "watching", otherwise +that data or critical section will not be protected as expected. In this +case add: + + if (!rcu_is_watching()) + return; + +Alternatively, if the FTRACE_OPS_FL_RCU flag is set on the ftrace_ops +(as explained below), then a helper trampoline will be used to test +for rcu_is_watching for the callback and no other test needs to be done. +But this is at the expense of a slightly more overhead from an extra +function call. + The ftrace FLAGS ================ @@ -128,26 +172,20 @@ FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED will not fail with this flag set. But the callback must check if regs is NULL or not to determine if the architecture supports it. -FTRACE_OPS_FL_RECURSION_SAFE - By default, a wrapper is added around the callback to - make sure that recursion of the function does not occur. That is, - if a function that is called as a result of the callback's execution - is also traced, ftrace will prevent the callback from being called - again. But this wrapper adds some overhead, and if the callback is - safe from recursion, it can set this flag to disable the ftrace - protection. - - Note, if this flag is set, and recursion does occur, it could cause - the system to crash, and possibly reboot via a triple fault. - - It is OK if another callback traces a function that is called by a - callback that is marked recursion safe. Recursion safe callbacks - must never trace any function that are called by the callback - itself or any nested functions that those functions call. - - If this flag is set, it is possible that the callback will also - be called with preemption enabled (when CONFIG_PREEMPTION is set), - but this is not guaranteed. +FTRACE_OPS_FL_RECURSION + By default, it is expected that the callback can handle recursion. + But if the callback is not that worried about overehead, then + setting this bit will add the recursion protection around the + callback by calling a helper function that will do the recursion + protection and only call the callback if it did not recurse. + + Note, if this flag is not set, and recursion does occur, it could + cause the system to crash, and possibly reboot via a triple fault. + + Not, if this flag is set, then the callback will always be called + with preemption disabled. If it is not set, then it is possible + (but not guaranteed) that the callback will be called in + preemptable context. FTRACE_OPS_FL_IPMODIFY Requires FTRACE_OPS_FL_SAVE_REGS set. If the callback is to "hijack" -- cgit v1.2.3-58-ga151 From 773c16705058e9be7b0f4ce124e89cd231c120a2 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Thu, 5 Nov 2020 21:32:46 -0500 Subject: ftrace: Add recording of functions that caused recursion This adds CONFIG_FTRACE_RECORD_RECURSION that will record to a file "recursed_functions" all the functions that caused recursion while a callback to the function tracer was running. Link: https://lkml.kernel.org/r/20201106023548.102375687@goodmis.org Cc: Masami Hiramatsu Cc: Andrew Morton Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Jonathan Corbet Cc: Guo Ren Cc: "James E.J. Bottomley" Cc: Helge Deller Cc: Michael Ellerman Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Thomas Gleixner Cc: Borislav Petkov Cc: x86@kernel.org Cc: "H. Peter Anvin" Cc: Kees Cook Cc: Anton Vorontsov Cc: Colin Cross Cc: Tony Luck Cc: Josh Poimboeuf Cc: Jiri Kosina Cc: Miroslav Benes Cc: Petr Mladek Cc: Joe Lawrence Cc: Kamalesh Babulal Cc: Mauro Carvalho Chehab Cc: Sebastian Andrzej Siewior Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-csky@vger.kernel.org Cc: linux-parisc@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-s390@vger.kernel.org Cc: live-patching@vger.kernel.org Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/ftrace-uses.rst | 6 +- arch/csky/kernel/probes/ftrace.c | 2 +- arch/parisc/kernel/ftrace.c | 2 +- arch/powerpc/kernel/kprobes-ftrace.c | 2 +- arch/s390/kernel/ftrace.c | 2 +- arch/x86/kernel/kprobes/ftrace.c | 2 +- fs/pstore/ftrace.c | 2 +- include/linux/trace_recursion.h | 29 ++++- kernel/livepatch/patch.c | 2 +- kernel/trace/Kconfig | 25 ++++ kernel/trace/Makefile | 1 + kernel/trace/ftrace.c | 4 +- kernel/trace/trace_event_perf.c | 2 +- kernel/trace/trace_functions.c | 2 +- kernel/trace/trace_output.c | 6 +- kernel/trace/trace_output.h | 1 + kernel/trace/trace_recursion_record.c | 236 ++++++++++++++++++++++++++++++++++ 17 files changed, 306 insertions(+), 20 deletions(-) create mode 100644 kernel/trace/trace_recursion_record.c (limited to 'Documentation/trace') diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 86cd14b8e126..5981d5691745 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -118,7 +118,7 @@ can help in this regard. If you start your code with: int bit; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; @@ -130,7 +130,9 @@ The code in between will be safe to use, even if it ends up calling a function that the callback is tracing. Note, on success, ftrace_test_recursion_trylock() will disable preemption, and the ftrace_test_recursion_unlock() will enable it again (if it was previously -enabled). +enabled). The instruction pointer (ip) and its parent (parent_ip) is passed to +ftrace_test_recursion_trylock() to record where the recursion happened +(if CONFIG_FTRACE_RECORD_RECURSION is set). Alternatively, if the FTRACE_OPS_FL_RECURSION flag is set on the ftrace_ops (as explained below), then a helper trampoline will be used to test diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c index 5eb2604fdf71..f30b179924ef 100644 --- a/arch/csky/kernel/probes/ftrace.c +++ b/arch/csky/kernel/probes/ftrace.c @@ -18,7 +18,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, struct kprobe *p; struct kprobe_ctlblk *kcb; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c index 13d85042810a..1c5d3732bda2 100644 --- a/arch/parisc/kernel/ftrace.c +++ b/arch/parisc/kernel/ftrace.c @@ -210,7 +210,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, struct kprobe *p; int bit; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c index 5df8d50c65ae..fdfee39938ea 100644 --- a/arch/powerpc/kernel/kprobes-ftrace.c +++ b/arch/powerpc/kernel/kprobes-ftrace.c @@ -20,7 +20,7 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, struct kprobe_ctlblk *kcb; int bit; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(nip, parent_nip); if (bit < 0) return; diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c index 8f31c726537a..657c1ab45408 100644 --- a/arch/s390/kernel/ftrace.c +++ b/arch/s390/kernel/ftrace.c @@ -204,7 +204,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, struct kprobe *p; int bit; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c index a40a6cdfcca3..954d930a7127 100644 --- a/arch/x86/kernel/kprobes/ftrace.c +++ b/arch/x86/kernel/kprobes/ftrace.c @@ -20,7 +20,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, struct kprobe_ctlblk *kcb; int bit; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c index 816210fc5d3a..adb0935eb062 100644 --- a/fs/pstore/ftrace.c +++ b/fs/pstore/ftrace.c @@ -41,7 +41,7 @@ static void notrace pstore_ftrace_call(unsigned long ip, if (unlikely(oops_in_progress)) return; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h index ac3d73484cb2..228cc56ed66e 100644 --- a/include/linux/trace_recursion.h +++ b/include/linux/trace_recursion.h @@ -91,6 +91,9 @@ enum { * not be correct. Allow for a single recursion to cover this case. */ TRACE_TRANSITION_BIT, + + /* Used to prevent recursion recording from recursing. */ + TRACE_RECORD_RECURSION_BIT, }; #define trace_recursion_set(bit) do { (current)->trace_recursion |= (1<<(bit)); } while (0) @@ -142,7 +145,22 @@ static __always_inline int trace_get_context_bit(void) pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ; } -static __always_inline int trace_test_and_set_recursion(int start, int max) +#ifdef CONFIG_FTRACE_RECORD_RECURSION +extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip); +# define do_ftrace_record_recursion(ip, pip) \ + do { \ + if (!trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \ + trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \ + ftrace_record_recursion(ip, pip); \ + trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \ + } \ + } while (0) +#else +# define do_ftrace_record_recursion(ip, pip) do { } while (0) +#endif + +static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip, + int start, int max) { unsigned int val = current->trace_recursion; int bit; @@ -158,8 +176,10 @@ static __always_inline int trace_test_and_set_recursion(int start, int max) * a switch between contexts. Allow for a single recursion. */ bit = TRACE_TRANSITION_BIT; - if (trace_recursion_test(bit)) + if (trace_recursion_test(bit)) { + do_ftrace_record_recursion(ip, pip); return -1; + } trace_recursion_set(bit); barrier(); return bit + 1; @@ -199,9 +219,10 @@ static __always_inline void trace_clear_recursion(int bit) * Returns: -1 if a recursion happened. * >= 0 if no recursion */ -static __always_inline int ftrace_test_recursion_trylock(void) +static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, + unsigned long parent_ip) { - return trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX); + return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX); } /** diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index 15480bf3ce88..875c5dbbdd33 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -49,7 +49,7 @@ static void notrace klp_ftrace_handler(unsigned long ip, ops = container_of(fops, struct klp_ops, fops); - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (WARN_ON_ONCE(bit < 0)) return; /* diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index a4020c0b4508..9b11c096d139 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -727,6 +727,31 @@ config TRACE_EVAL_MAP_FILE If unsure, say N. +config FTRACE_RECORD_RECURSION + bool "Record functions that recurse in function tracing" + depends on FUNCTION_TRACER + help + All callbacks that attach to the function tracing have some sort + of protection against recursion. Even though the protection exists, + it adds overhead. This option will create a file in the tracefs + file system called "recursed_functions" that will list the functions + that triggered a recursion. + + This will add more overhead to cases that have recursion. + + If unsure, say N + +config FTRACE_RECORD_RECURSION_SIZE + int "Max number of recursed functions to record" + default 128 + depends on FTRACE_RECORD_RECURSION + help + This defines the limit of number of functions that can be + listed in the "recursed_functions" file, that lists all + the functions that caused a recursion to happen. + This file can be reset, but the limit can not change in + size at runtime. + config GCOV_PROFILE_FTRACE bool "Enable GCOV profiling on ftrace subsystem" depends on GCOV_KERNEL diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index e153be351548..7e44cea89fdc 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -92,6 +92,7 @@ obj-$(CONFIG_DYNAMIC_EVENTS) += trace_dynevent.o obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o +obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 39f2bba89b76..03aad2b5cd5e 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6918,7 +6918,7 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip, struct ftrace_ops *op; int bit; - bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX); + bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START, TRACE_LIST_MAX); if (bit < 0) return; @@ -6993,7 +6993,7 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip, { int bit; - bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX); + bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START, TRACE_LIST_MAX); if (bit < 0) return; diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c index a2b9fddb8148..1b202e28dfaa 100644 --- a/kernel/trace/trace_event_perf.c +++ b/kernel/trace/trace_event_perf.c @@ -447,7 +447,7 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip, if ((unsigned long)ops->private != smp_processor_id()) return; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c index 89c414ce1388..646eda6c44a5 100644 --- a/kernel/trace/trace_functions.c +++ b/kernel/trace/trace_functions.c @@ -141,7 +141,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip, if (unlikely(!tr->function_enabled)) return; - bit = ftrace_test_recursion_trylock(); + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 000e9dc224c6..92b1575ae0ca 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -353,8 +353,8 @@ static inline const char *kretprobed(const char *name) } #endif /* CONFIG_KRETPROBES */ -static void -seq_print_sym(struct trace_seq *s, unsigned long address, bool offset) +void +trace_seq_print_sym(struct trace_seq *s, unsigned long address, bool offset) { #ifdef CONFIG_KALLSYMS char str[KSYM_SYMBOL_LEN]; @@ -420,7 +420,7 @@ seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags) goto out; } - seq_print_sym(s, ip, sym_flags & TRACE_ITER_SYM_OFFSET); + trace_seq_print_sym(s, ip, sym_flags & TRACE_ITER_SYM_OFFSET); if (sym_flags & TRACE_ITER_SYM_ADDR) trace_seq_printf(s, " <" IP_FMT ">", ip); diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h index 2f742b74e7e6..4c954636caf0 100644 --- a/kernel/trace/trace_output.h +++ b/kernel/trace/trace_output.h @@ -16,6 +16,7 @@ extern int seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags); +extern void trace_seq_print_sym(struct trace_seq *s, unsigned long address, bool offset); extern int trace_print_context(struct trace_iterator *iter); extern int trace_print_lat_context(struct trace_iterator *iter); diff --git a/kernel/trace/trace_recursion_record.c b/kernel/trace/trace_recursion_record.c new file mode 100644 index 000000000000..b2edac1fe156 --- /dev/null +++ b/kernel/trace/trace_recursion_record.c @@ -0,0 +1,236 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include +#include + +#include "trace_output.h" + +struct recursed_functions { + unsigned long ip; + unsigned long parent_ip; +}; + +static struct recursed_functions recursed_functions[CONFIG_FTRACE_RECORD_RECURSION_SIZE]; +static atomic_t nr_records; + +/* + * Cache the last found function. Yes, updates to this is racey, but + * so is memory cache ;-) + */ +static unsigned long cached_function; + +void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip) +{ + int index = 0; + int i; + unsigned long old; + + again: + /* First check the last one recorded */ + if (ip == cached_function) + return; + + i = atomic_read(&nr_records); + /* nr_records is -1 when clearing records */ + smp_mb__after_atomic(); + if (i < 0) + return; + + /* + * If there's two writers and this writer comes in second, + * the cmpxchg() below to update the ip will fail. Then this + * writer will try again. It is possible that index will now + * be greater than nr_records. This is because the writer + * that succeeded has not updated the nr_records yet. + * This writer could keep trying again until the other writer + * updates nr_records. But if the other writer takes an + * interrupt, and that interrupt locks up that CPU, we do + * not want this CPU to lock up due to the recursion protection, + * and have a bug report showing this CPU as the cause of + * locking up the computer. To not lose this record, this + * writer will simply use the next position to update the + * recursed_functions, and it will update the nr_records + * accordingly. + */ + if (index < i) + index = i; + if (index >= CONFIG_FTRACE_RECORD_RECURSION_SIZE) + return; + + for (i = index - 1; i >= 0; i--) { + if (recursed_functions[i].ip == ip) { + cached_function = ip; + return; + } + } + + cached_function = ip; + + /* + * We only want to add a function if it hasn't been added before. + * Add to the current location before incrementing the count. + * If it fails to add, then increment the index (save in i) + * and try again. + */ + old = cmpxchg(&recursed_functions[index].ip, 0, ip); + if (old != 0) { + /* Did something else already added this for us? */ + if (old == ip) + return; + /* Try the next location (use i for the next index) */ + index++; + goto again; + } + + recursed_functions[index].parent_ip = parent_ip; + + /* + * It's still possible that we could race with the clearing + * CPU0 CPU1 + * ---- ---- + * ip = func + * nr_records = -1; + * recursed_functions[0] = 0; + * i = -1 + * if (i < 0) + * nr_records = 0; + * (new recursion detected) + * recursed_functions[0] = func + * cmpxchg(recursed_functions[0], + * func, 0) + * + * But the worse that could happen is that we get a zero in + * the recursed_functions array, and it's likely that "func" will + * be recorded again. + */ + i = atomic_read(&nr_records); + smp_mb__after_atomic(); + if (i < 0) + cmpxchg(&recursed_functions[index].ip, ip, 0); + else if (i <= index) + atomic_cmpxchg(&nr_records, i, index + 1); +} +EXPORT_SYMBOL_GPL(ftrace_record_recursion); + +static DEFINE_MUTEX(recursed_function_lock); +static struct trace_seq *tseq; + +static void *recursed_function_seq_start(struct seq_file *m, loff_t *pos) +{ + void *ret = NULL; + int index; + + mutex_lock(&recursed_function_lock); + index = atomic_read(&nr_records); + if (*pos < index) { + ret = &recursed_functions[*pos]; + } + + tseq = kzalloc(sizeof(*tseq), GFP_KERNEL); + if (!tseq) + return ERR_PTR(-ENOMEM); + + trace_seq_init(tseq); + + return ret; +} + +static void *recursed_function_seq_next(struct seq_file *m, void *v, loff_t *pos) +{ + int index; + int p; + + index = atomic_read(&nr_records); + p = ++(*pos); + + return p < index ? &recursed_functions[p] : NULL; +} + +static void recursed_function_seq_stop(struct seq_file *m, void *v) +{ + kfree(tseq); + mutex_unlock(&recursed_function_lock); +} + +static int recursed_function_seq_show(struct seq_file *m, void *v) +{ + struct recursed_functions *record = v; + int ret = 0; + + if (record) { + trace_seq_print_sym(tseq, record->parent_ip, true); + trace_seq_puts(tseq, ":\t"); + trace_seq_print_sym(tseq, record->ip, true); + trace_seq_putc(tseq, '\n'); + ret = trace_print_seq(m, tseq); + } + + return ret; +} + +static const struct seq_operations recursed_function_seq_ops = { + .start = recursed_function_seq_start, + .next = recursed_function_seq_next, + .stop = recursed_function_seq_stop, + .show = recursed_function_seq_show +}; + +static int recursed_function_open(struct inode *inode, struct file *file) +{ + int ret = 0; + + mutex_lock(&recursed_function_lock); + /* If this file was opened for write, then erase contents */ + if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) { + /* disable updating records */ + atomic_set(&nr_records, -1); + smp_mb__after_atomic(); + memset(recursed_functions, 0, sizeof(recursed_functions)); + smp_wmb(); + /* enable them again */ + atomic_set(&nr_records, 0); + } + if (file->f_mode & FMODE_READ) + ret = seq_open(file, &recursed_function_seq_ops); + mutex_unlock(&recursed_function_lock); + + return ret; +} + +static ssize_t recursed_function_write(struct file *file, + const char __user *buffer, + size_t count, loff_t *ppos) +{ + return count; +} + +static int recursed_function_release(struct inode *inode, struct file *file) +{ + if (file->f_mode & FMODE_READ) + seq_release(inode, file); + return 0; +} + +static const struct file_operations recursed_functions_fops = { + .open = recursed_function_open, + .write = recursed_function_write, + .read = seq_read, + .llseek = seq_lseek, + .release = recursed_function_release, +}; + +__init static int create_recursed_functions(void) +{ + struct dentry *dentry; + + dentry = trace_create_file("recursed_functions", 0644, NULL, NULL, + &recursed_functions_fops); + if (!dentry) + pr_warn("WARNING: Failed to create recursed_functions\n"); + return 0; +} + +fs_initcall(create_recursed_functions); -- cgit v1.2.3-58-ga151 From 3a37b918946e04da7902b83917764f73cc0bd90c Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Mon, 16 Nov 2020 15:46:52 -0500 Subject: ftrace/documentation: Fix RST C code blocks Some C code in the ftrace-users.rst document is missing RST C block annotation, which has to be added. Link: https://lore.kernel.org/r/20201116173502.392a769c@canb.auug.org.au Acked-by: Jonathan Corbet Reported-by: Stephen Rothwell Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/ftrace-uses.rst | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation/trace') diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 5981d5691745..f7d98ae5b885 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -116,6 +116,8 @@ called by a callback may also be traced, and call that same callback, recursion protection must be used. There are two helper functions that can help in this regard. If you start your code with: +.. code-block:: c + int bit; bit = ftrace_test_recursion_trylock(ip, parent_ip); @@ -124,6 +126,8 @@ can help in this regard. If you start your code with: and end it with: +.. code-block:: c + ftrace_test_recursion_unlock(bit); The code in between will be safe to use, even if it ends up calling a @@ -145,6 +149,8 @@ protection, it is best to make sure that RCU is "watching", otherwise that data or critical section will not be protected as expected. In this case add: +.. code-block:: c + if (!rcu_is_watching()) return; -- cgit v1.2.3-58-ga151