diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2020-05-08 14:58:28 +0200 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2020-05-08 14:58:28 +0200 |
commit | 97a9474aeb789183a1d0712e66a4283860279ac9 (patch) | |
tree | 4cd94285ef4a8e81c8d2e28f7dc9923cb60014e4 /kernel/kcsan/report.c | |
parent | 3b02a051d25d9600e9d403ad3043aed7de00160e (diff) | |
parent | 50a19ad4b1ec531eb550183cb5d4ab9f25a56bf8 (diff) |
Merge branch 'kcsan-for-tip' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/kcsan
Pull KCSAN updates from Paul McKenney.
Diffstat (limited to 'kernel/kcsan/report.c')
-rw-r--r-- | kernel/kcsan/report.c | 455 |
1 files changed, 287 insertions, 168 deletions
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c index 11c791b886f3..ac5f8345bae9 100644 --- a/kernel/kcsan/report.c +++ b/kernel/kcsan/report.c @@ -1,5 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 +#include <linux/debug_locks.h> +#include <linux/delay.h> #include <linux/jiffies.h> #include <linux/kernel.h> #include <linux/lockdep.h> @@ -17,21 +19,49 @@ */ #define NUM_STACK_ENTRIES 64 -/* - * Other thread info: communicated from other racing thread to thread that set - * up the watchpoint, which then prints the complete report atomically. Only - * need one struct, as all threads should to be serialized regardless to print - * the reports, with reporting being in the slow-path. - */ -static struct { +/* Common access info. */ +struct access_info { const volatile void *ptr; size_t size; int access_type; int task_pid; int cpu_id; +}; + +/* + * Other thread info: communicated from other racing thread to thread that set + * up the watchpoint, which then prints the complete report atomically. + */ +struct other_info { + struct access_info ai; unsigned long stack_entries[NUM_STACK_ENTRIES]; int num_stack_entries; -} other_info = { .ptr = NULL }; + + /* + * Optionally pass @current. Typically we do not need to pass @current + * via @other_info since just @task_pid is sufficient. Passing @current + * has additional overhead. + * + * To safely pass @current, we must either use get_task_struct/ + * put_task_struct, or stall the thread that populated @other_info. + * + * We cannot rely on get_task_struct/put_task_struct in case + * release_report() races with a task being released, and would have to + * free it in release_report(). This may result in deadlock if we want + * to use KCSAN on the allocators. + * + * Since we also want to reliably print held locks for + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread + * that populated @other_info until it has been consumed. + */ + struct task_struct *task; +}; + +/* + * To never block any producers of struct other_info, we need as many elements + * as we have watchpoints (upper bound on concurrent races to report). + */ +static struct other_info other_infos[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1]; /* * Information about reported races; used to rate limit reporting. @@ -68,10 +98,11 @@ struct report_time { static struct report_time report_times[REPORT_TIMES_SIZE]; /* - * This spinlock protects reporting and other_info, since other_info is usually - * required when reporting. + * Spinlock serializing report generation, and access to @other_infos. Although + * it could make sense to have a finer-grained locking story for @other_infos, + * report generation needs to be serialized either way, so not much is gained. */ -static DEFINE_SPINLOCK(report_lock); +static DEFINE_RAW_SPINLOCK(report_lock); /* * Checks if the race identified by thread frames frame1 and frame2 has @@ -161,11 +192,11 @@ skip_report(enum kcsan_value_change value_change, unsigned long top_frame) * maintainers. */ char buf[64]; + int len = scnprintf(buf, sizeof(buf), "%ps", (void *)top_frame); - snprintf(buf, sizeof(buf), "%ps", (void *)top_frame); - if (!strnstr(buf, "rcu_", sizeof(buf)) && - !strnstr(buf, "_rcu", sizeof(buf)) && - !strnstr(buf, "_srcu", sizeof(buf))) + if (!strnstr(buf, "rcu_", len) && + !strnstr(buf, "_rcu", len) && + !strnstr(buf, "_srcu", len)) return true; } @@ -174,6 +205,20 @@ skip_report(enum kcsan_value_change value_change, unsigned long top_frame) static const char *get_access_type(int type) { + if (type & KCSAN_ACCESS_ASSERT) { + if (type & KCSAN_ACCESS_SCOPED) { + if (type & KCSAN_ACCESS_WRITE) + return "assert no accesses (scoped)"; + else + return "assert no writes (scoped)"; + } else { + if (type & KCSAN_ACCESS_WRITE) + return "assert no accesses"; + else + return "assert no writes"; + } + } + switch (type) { case 0: return "read"; @@ -183,17 +228,14 @@ static const char *get_access_type(int type) return "write"; case KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC: return "write (marked)"; - - /* - * ASSERT variants: - */ - case KCSAN_ACCESS_ASSERT: - case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_ATOMIC: - return "assert no writes"; - case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE: - case KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC: - return "assert no accesses"; - + case KCSAN_ACCESS_SCOPED: + return "read (scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_ATOMIC: + return "read (marked, scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE: + return "write (scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC: + return "write (marked, scoped)"; default: BUG(); } @@ -217,19 +259,35 @@ static const char *get_thread_desc(int task_id) } /* Helper to skip KCSAN-related functions in stack-trace. */ -static int get_stack_skipnr(unsigned long stack_entries[], int num_entries) +static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries) { char buf[64]; - int skip = 0; - - for (; skip < num_entries; ++skip) { - snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]); - if (!strnstr(buf, "csan_", sizeof(buf)) && - !strnstr(buf, "tsan_", sizeof(buf)) && - !strnstr(buf, "_once_size", sizeof(buf))) { - break; + char *cur; + int len, skip; + + for (skip = 0; skip < num_entries; ++skip) { + len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]); + + /* Never show tsan_* or {read,write}_once_size. */ + if (strnstr(buf, "tsan_", len) || + strnstr(buf, "_once_size", len)) + continue; + + cur = strnstr(buf, "kcsan_", len); + if (cur) { + cur += sizeof("kcsan_") - 1; + if (strncmp(cur, "test", sizeof("test") - 1)) + continue; /* KCSAN runtime function. */ + /* KCSAN related test. */ } + + /* + * No match for runtime functions -- @skip entries to skip to + * get to first frame of interest. + */ + break; } + return skip; } @@ -245,12 +303,23 @@ static int sym_strcmp(void *addr1, void *addr2) return strncmp(buf1, buf2, sizeof(buf1)); } +static void print_verbose_info(struct task_struct *task) +{ + if (!task) + return; + + pr_err("\n"); + debug_show_held_locks(task); + print_irqtrace_events(task); +} + /* * Returns true if a report was generated, false otherwise. */ -static bool print_report(const volatile void *ptr, size_t size, int access_type, - enum kcsan_value_change value_change, int cpu_id, - enum kcsan_report_type type) +static bool print_report(enum kcsan_value_change value_change, + enum kcsan_report_type type, + const struct access_info *ai, + const struct other_info *other_info) { unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 }; int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1); @@ -266,9 +335,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, return false; if (type == KCSAN_REPORT_RACE_SIGNAL) { - other_skipnr = get_stack_skipnr(other_info.stack_entries, - other_info.num_stack_entries); - other_frame = other_info.stack_entries[other_skipnr]; + other_skipnr = get_stack_skipnr(other_info->stack_entries, + other_info->num_stack_entries); + other_frame = other_info->stack_entries[other_skipnr]; /* @value_change is only known for the other thread */ if (skip_report(value_change, other_frame)) @@ -290,13 +359,13 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, */ cmp = sym_strcmp((void *)other_frame, (void *)this_frame); pr_err("BUG: KCSAN: %s in %ps / %ps\n", - get_bug_type(access_type | other_info.access_type), + get_bug_type(ai->access_type | other_info->ai.access_type), (void *)(cmp < 0 ? other_frame : this_frame), (void *)(cmp < 0 ? this_frame : other_frame)); } break; case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: - pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(access_type), + pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(ai->access_type), (void *)this_frame); break; @@ -310,27 +379,28 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, switch (type) { case KCSAN_REPORT_RACE_SIGNAL: pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", - get_access_type(other_info.access_type), other_info.ptr, - other_info.size, get_thread_desc(other_info.task_pid), - other_info.cpu_id); + get_access_type(other_info->ai.access_type), other_info->ai.ptr, + other_info->ai.size, get_thread_desc(other_info->ai.task_pid), + other_info->ai.cpu_id); /* Print the other thread's stack trace. */ - stack_trace_print(other_info.stack_entries + other_skipnr, - other_info.num_stack_entries - other_skipnr, + stack_trace_print(other_info->stack_entries + other_skipnr, + other_info->num_stack_entries - other_skipnr, 0); + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + print_verbose_info(other_info->task); + pr_err("\n"); pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", - get_access_type(access_type), ptr, size, - get_thread_desc(in_task() ? task_pid_nr(current) : -1), - cpu_id); + get_access_type(ai->access_type), ai->ptr, ai->size, + get_thread_desc(ai->task_pid), ai->cpu_id); break; case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n", - get_access_type(access_type), ptr, size, - get_thread_desc(in_task() ? task_pid_nr(current) : -1), - cpu_id); + get_access_type(ai->access_type), ai->ptr, ai->size, + get_thread_desc(ai->task_pid), ai->cpu_id); break; default: @@ -340,6 +410,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0); + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + print_verbose_info(current); + /* Print report footer. */ pr_err("\n"); pr_err("Reported by Kernel Concurrency Sanitizer on:\n"); @@ -349,142 +422,188 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, return true; } -static void release_report(unsigned long *flags, enum kcsan_report_type type) +static void release_report(unsigned long *flags, struct other_info *other_info) { - if (type == KCSAN_REPORT_RACE_SIGNAL) - other_info.ptr = NULL; /* mark for reuse */ + if (other_info) + /* + * Use size to denote valid/invalid, since KCSAN entirely + * ignores 0-sized accesses. + */ + other_info->ai.size = 0; - spin_unlock_irqrestore(&report_lock, *flags); + raw_spin_unlock_irqrestore(&report_lock, *flags); } /* - * Depending on the report type either sets other_info and returns false, or - * acquires the matching other_info and returns true. If other_info is not - * required for the report type, simply acquires report_lock and returns true. + * Sets @other_info->task and awaits consumption of @other_info. + * + * Precondition: report_lock is held. + * Postcondition: report_lock is held. */ -static bool prepare_report(unsigned long *flags, const volatile void *ptr, - size_t size, int access_type, int cpu_id, - enum kcsan_report_type type) +static void set_other_info_task_blocking(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) { - if (type != KCSAN_REPORT_CONSUMED_WATCHPOINT && - type != KCSAN_REPORT_RACE_SIGNAL) { - /* other_info not required; just acquire report_lock */ - spin_lock_irqsave(&report_lock, *flags); - return true; - } + /* + * We may be instrumenting a code-path where current->state is already + * something other than TASK_RUNNING. + */ + const bool is_running = current->state == TASK_RUNNING; + /* + * To avoid deadlock in case we are in an interrupt here and this is a + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a + * timeout to ensure this works in all contexts. + * + * Await approximately the worst case delay of the reporting thread (if + * we are not interrupted). + */ + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt); + + other_info->task = current; + do { + if (is_running) { + /* + * Let lockdep know the real task is sleeping, to print + * the held locks (recall we turned lockdep off, so + * locking/unlocking @report_lock won't be recorded). + */ + set_current_state(TASK_UNINTERRUPTIBLE); + } + raw_spin_unlock_irqrestore(&report_lock, *flags); + /* + * We cannot call schedule() since we also cannot reliably + * determine if sleeping here is permitted -- see in_atomic(). + */ -retry: - spin_lock_irqsave(&report_lock, *flags); + udelay(1); + raw_spin_lock_irqsave(&report_lock, *flags); + if (timeout-- < 0) { + /* + * Abort. Reset @other_info->task to NULL, since it + * appears the other thread is still going to consume + * it. It will result in no verbose info printed for + * this task. + */ + other_info->task = NULL; + break; + } + /* + * If invalid, or @ptr nor @current matches, then @other_info + * has been consumed and we may continue. If not, retry. + */ + } while (other_info->ai.size && other_info->ai.ptr == ai->ptr && + other_info->task == current); + if (is_running) + set_current_state(TASK_RUNNING); +} - switch (type) { - case KCSAN_REPORT_CONSUMED_WATCHPOINT: - if (other_info.ptr != NULL) - break; /* still in use, retry */ +/* Populate @other_info; requires that the provided @other_info not in use. */ +static void prepare_report_producer(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) +{ + raw_spin_lock_irqsave(&report_lock, *flags); - other_info.ptr = ptr; - other_info.size = size; - other_info.access_type = access_type; - other_info.task_pid = in_task() ? task_pid_nr(current) : -1; - other_info.cpu_id = cpu_id; - other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1); + /* + * The same @other_infos entry cannot be used concurrently, because + * there is a one-to-one mapping to watchpoint slots (@watchpoints in + * core.c), and a watchpoint is only released for reuse after reporting + * is done by the consumer of @other_info. Therefore, it is impossible + * for another concurrent prepare_report_producer() to set the same + * @other_info, and are guaranteed exclusivity for the @other_infos + * entry pointed to by @other_info. + * + * To check this property holds, size should never be non-zero here, + * because every consumer of struct other_info resets size to 0 in + * release_report(). + */ + WARN_ON(other_info->ai.size); - spin_unlock_irqrestore(&report_lock, *flags); + other_info->ai = *ai; + other_info->num_stack_entries = stack_trace_save(other_info->stack_entries, NUM_STACK_ENTRIES, 2); - /* - * The other thread will print the summary; other_info may now - * be consumed. - */ - return false; + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + set_other_info_task_blocking(flags, ai, other_info); - case KCSAN_REPORT_RACE_SIGNAL: - if (other_info.ptr == NULL) - break; /* no data available yet, retry */ + raw_spin_unlock_irqrestore(&report_lock, *flags); +} - /* - * First check if this is the other_info we are expecting, i.e. - * matches based on how watchpoint was encoded. - */ - if (!matching_access((unsigned long)other_info.ptr & - WATCHPOINT_ADDR_MASK, - other_info.size, - (unsigned long)ptr & WATCHPOINT_ADDR_MASK, - size)) - break; /* mismatching watchpoint, retry */ - - if (!matching_access((unsigned long)other_info.ptr, - other_info.size, (unsigned long)ptr, - size)) { - /* - * If the actual accesses to not match, this was a false - * positive due to watchpoint encoding. - */ - kcsan_counter_inc( - KCSAN_COUNTER_ENCODING_FALSE_POSITIVES); +/* Awaits producer to fill @other_info and then returns. */ +static bool prepare_report_consumer(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) +{ - /* discard this other_info */ - release_report(flags, KCSAN_REPORT_RACE_SIGNAL); - return false; - } + raw_spin_lock_irqsave(&report_lock, *flags); + while (!other_info->ai.size) { /* Await valid @other_info. */ + raw_spin_unlock_irqrestore(&report_lock, *flags); + cpu_relax(); + raw_spin_lock_irqsave(&report_lock, *flags); + } - access_type |= other_info.access_type; - if ((access_type & KCSAN_ACCESS_WRITE) == 0) { - /* - * While the address matches, this is not the other_info - * from the thread that consumed our watchpoint, since - * neither this nor the access in other_info is a write. - * It is invalid to continue with the report, since we - * only have information about reads. - * - * This can happen due to concurrent races on the same - * address, with at least 4 threads. To avoid locking up - * other_info and all other threads, we have to consume - * it regardless. - * - * A concrete case to illustrate why we might lock up if - * we do not consume other_info: - * - * We have 4 threads, all accessing the same address - * (or matching address ranges). Assume the following - * watcher and watchpoint consumer pairs: - * write1-read1, read2-write2. The first to populate - * other_info is write2, however, write1 consumes it, - * resulting in a report of write1-write2. This report - * is valid, however, now read1 populates other_info; - * read2-read1 is an invalid conflict, yet, no other - * conflicting access is left. Therefore, we must - * consume read1's other_info. - * - * Since this case is assumed to be rare, it is - * reasonable to omit this report: one of the other - * reports includes information about the same shared - * data, and at this point the likelihood that we - * re-report the same race again is high. - */ - release_report(flags, KCSAN_REPORT_RACE_SIGNAL); - return false; - } + /* Should always have a matching access based on watchpoint encoding. */ + if (WARN_ON(!matching_access((unsigned long)other_info->ai.ptr & WATCHPOINT_ADDR_MASK, other_info->ai.size, + (unsigned long)ai->ptr & WATCHPOINT_ADDR_MASK, ai->size))) + goto discard; + if (!matching_access((unsigned long)other_info->ai.ptr, other_info->ai.size, + (unsigned long)ai->ptr, ai->size)) { /* - * Matching & usable access in other_info: keep other_info_lock - * locked, as this thread consumes it to print the full report; - * unlocked in release_report. + * If the actual accesses to not match, this was a false + * positive due to watchpoint encoding. */ - return true; - - default: - BUG(); + kcsan_counter_inc(KCSAN_COUNTER_ENCODING_FALSE_POSITIVES); + goto discard; } - spin_unlock_irqrestore(&report_lock, *flags); + return true; - goto retry; +discard: + release_report(flags, other_info); + return false; +} + +/* + * Depending on the report type either sets @other_info and returns false, or + * awaits @other_info and returns true. If @other_info is not required for the + * report type, simply acquires @report_lock and returns true. + */ +static noinline bool prepare_report(unsigned long *flags, + enum kcsan_report_type type, + const struct access_info *ai, + struct other_info *other_info) +{ + switch (type) { + case KCSAN_REPORT_CONSUMED_WATCHPOINT: + prepare_report_producer(flags, ai, other_info); + return false; + case KCSAN_REPORT_RACE_SIGNAL: + return prepare_report_consumer(flags, ai, other_info); + default: + /* @other_info not required; just acquire @report_lock. */ + raw_spin_lock_irqsave(&report_lock, *flags); + return true; + } } void kcsan_report(const volatile void *ptr, size_t size, int access_type, - enum kcsan_value_change value_change, int cpu_id, - enum kcsan_report_type type) + enum kcsan_value_change value_change, + enum kcsan_report_type type, int watchpoint_idx) { unsigned long flags = 0; + const struct access_info ai = { + .ptr = ptr, + .size = size, + .access_type = access_type, + .task_pid = in_task() ? task_pid_nr(current) : -1, + .cpu_id = raw_smp_processor_id() + }; + struct other_info *other_info = type == KCSAN_REPORT_RACE_UNKNOWN_ORIGIN + ? NULL : &other_infos[watchpoint_idx]; + + kcsan_disable_current(); + if (WARN_ON(watchpoint_idx < 0 || watchpoint_idx >= ARRAY_SIZE(other_infos))) + goto out; /* * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if @@ -494,22 +613,22 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, */ lockdep_off(); - kcsan_disable_current(); - if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) { + if (prepare_report(&flags, type, &ai, other_info)) { /* * Never report if value_change is FALSE, only if we it is * either TRUE or MAYBE. In case of MAYBE, further filtering may * be done once we know the full stack trace in print_report(). */ bool reported = value_change != KCSAN_VALUE_CHANGE_FALSE && - print_report(ptr, size, access_type, value_change, cpu_id, type); + print_report(value_change, type, &ai, other_info); if (reported && panic_on_warn) panic("panic_on_warn set ...\n"); - release_report(&flags, type); + release_report(&flags, other_info); } - kcsan_enable_current(); lockdep_on(); +out: + kcsan_enable_current(); } |