From 3b7ddab8a19aefc768f345fd3782af35b4a68d9b Mon Sep 17 00:00:00 2001 From: wuqiang Date: Thu, 10 Nov 2022 16:15:02 +0800 Subject: kprobes: kretprobe events missing on 2-core KVM guest Default value of maxactive is set as num_possible_cpus() for nonpreemptable systems. For a 2-core system, only 2 kretprobe instances would be allocated in default, then these 2 instances for execve kretprobe are very likely to be used up with a pipelined command. Here's the testcase: a shell script was added to crontab, and the content of the script is: #!/bin/sh do_something_magic `tr -dc a-z < /dev/urandom | head -c 10` cron will trigger a series of program executions (4 times every hour). Then events loss would be noticed normally after 3-4 hours of testings. The issue is caused by a burst of series of execve requests. The best number of kretprobe instances could be different case by case, and should be user's duty to determine, but num_possible_cpus() as the default value is inadequate especially for systems with small number of cpus. This patch enables the logic for preemption as default, thus increases the minimum of maxactive to 10 for nonpreemptable systems. Link: https://lore.kernel.org/all/20221110081502.492289-1-wuqiang.matt@bytedance.com/ Signed-off-by: wuqiang Reviewed-by: Solar Designer Acked-by: Masami Hiramatsu (Google) Signed-off-by: Masami Hiramatsu (Google) --- Documentation/trace/kprobes.rst | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'Documentation/trace') diff --git a/Documentation/trace/kprobes.rst b/Documentation/trace/kprobes.rst index 48cf778a2468..fc7ce76eab65 100644 --- a/Documentation/trace/kprobes.rst +++ b/Documentation/trace/kprobes.rst @@ -131,8 +131,7 @@ For example, if the function is non-recursive and is called with a spinlock held, maxactive = 1 should be enough. If the function is non-recursive and can never relinquish the CPU (e.g., via a semaphore or preemption), NR_CPUS should be enough. If maxactive <= 0, it is -set to a default value. If CONFIG_PREEMPT is enabled, the default -is max(10, 2*NR_CPUS). Otherwise, the default is NR_CPUS. +set to a default value: max(10, 2*NR_CPUS). It's not a disaster if you set maxactive too low; you'll just miss some probes. In the kretprobe struct, the nmissed field is set to -- cgit v1.2.3 From b26a124cbfa80f42bfc4e63e1d5643ca98159d66 Mon Sep 17 00:00:00 2001 From: "Masami Hiramatsu (Google)" Date: Mon, 14 Nov 2022 13:47:56 +0900 Subject: tracing/probes: Add symstr type for dynamic events Add 'symstr' type for storing the kernel symbol as a string data instead of the symbol address. This allows us to filter the events by wildcard symbol name. e.g. # echo 'e:wqfunc workqueue.workqueue_execute_start symname=$function:symstr' >> dynamic_events # cat events/eprobes/wqfunc/format name: wqfunc ID: 2110 format: field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_preempt_count; offset:3; size:1; signed:0; field:int common_pid; offset:4; size:4; signed:1; field:__data_loc char[] symname; offset:8; size:4; signed:1; print fmt: " symname=\"%s\"", __get_str(symname) Note that there is already 'symbol' type which just change the print format (so it still stores the symbol address in the tracing ring buffer.) On the other hand, 'symstr' type stores the actual "symbol+offset/size" data as a string. Link: https://lore.kernel.org/all/166679930847.1528100.4124308529180235965.stgit@devnote3/ Signed-off-by: Masami Hiramatsu (Google) --- Documentation/trace/kprobetrace.rst | 8 +++++-- kernel/trace/trace.c | 2 +- kernel/trace/trace_probe.c | 44 ++++++++++++++++++++++------------ kernel/trace/trace_probe.h | 16 +++++++++---- kernel/trace/trace_probe_tmpl.h | 47 ++++++++++++++++++++++++++++++++++--- 5 files changed, 91 insertions(+), 26 deletions(-) (limited to 'Documentation/trace') diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst index 4274cc6a2f94..08a2a6a3782f 100644 --- a/Documentation/trace/kprobetrace.rst +++ b/Documentation/trace/kprobetrace.rst @@ -58,8 +58,8 @@ Synopsis of kprobe_events NAME=FETCHARG : Set NAME as the argument name of FETCHARG. FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types - (x8/x16/x32/x64), "string", "ustring" and bitfield - are supported. + (x8/x16/x32/x64), "string", "ustring", "symbol", "symstr" + and bitfield are supported. (\*1) only for the probe on function entry (offs == 0). (\*2) only for return probe. @@ -96,6 +96,10 @@ offset, and container-size (usually 32). The syntax is:: Symbol type('symbol') is an alias of u32 or u64 type (depends on BITS_PER_LONG) which shows given pointer in "symbol+offset" style. +On the other hand, symbol-string type ('symstr') converts the given address to +"symbol+offset/symbolsize" style and stores it as a null-terminated string. +With 'symstr' type, you can filter the event with wildcard pattern of the +symbols, and you don't need to solve symbol name by yourself. For $comm, the default type is "string"; any other type is invalid. .. _user_mem_access: diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index c6c7a0af3ed2..9ee519ad164e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5608,7 +5608,7 @@ static const char readme_msg[] = "\t +|-[u](), \\imm-value, \\\"imm-string\"\n" "\t type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n" "\t b@/, ustring,\n" - "\t \\[\\]\n" + "\t symstr, \\[\\]\n" #ifdef CONFIG_HIST_TRIGGERS "\t field: ;\n" "\t stype: u8/u16/u32/u64, s8/s16/s32/s64, pid_t,\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 36dff277de46..dfec4af857b4 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -76,9 +76,11 @@ const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\""; /* Fetch type information table */ static const struct fetch_type probe_fetch_types[] = { /* Special types */ - __ASSIGN_FETCH_TYPE("string", string, string, sizeof(u32), 1, + __ASSIGN_FETCH_TYPE("string", string, string, sizeof(u32), 1, 1, "__data_loc char[]"), - __ASSIGN_FETCH_TYPE("ustring", string, string, sizeof(u32), 1, + __ASSIGN_FETCH_TYPE("ustring", string, string, sizeof(u32), 1, 1, + "__data_loc char[]"), + __ASSIGN_FETCH_TYPE("symstr", string, string, sizeof(u32), 1, 1, "__data_loc char[]"), /* Basic types */ ASSIGN_FETCH_TYPE(u8, u8, 0), @@ -662,16 +664,26 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size, ret = -EINVAL; /* Store operation */ - if (!strcmp(parg->type->name, "string") || - !strcmp(parg->type->name, "ustring")) { - if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF && - code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM && - code->op != FETCH_OP_DATA && code->op != FETCH_OP_TP_ARG) { - trace_probe_log_err(offset + (t ? (t - arg) : 0), - BAD_STRING); - goto fail; + if (parg->type->is_string) { + if (!strcmp(parg->type->name, "symstr")) { + if (code->op != FETCH_OP_REG && code->op != FETCH_OP_STACK && + code->op != FETCH_OP_RETVAL && code->op != FETCH_OP_ARG && + code->op != FETCH_OP_DEREF && code->op != FETCH_OP_TP_ARG) { + trace_probe_log_err(offset + (t ? (t - arg) : 0), + BAD_SYMSTRING); + goto fail; + } + } else { + if (code->op != FETCH_OP_DEREF && code->op != FETCH_OP_UDEREF && + code->op != FETCH_OP_IMM && code->op != FETCH_OP_COMM && + code->op != FETCH_OP_DATA && code->op != FETCH_OP_TP_ARG) { + trace_probe_log_err(offset + (t ? (t - arg) : 0), + BAD_STRING); + goto fail; + } } - if ((code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM || + if (!strcmp(parg->type->name, "symstr") || + (code->op == FETCH_OP_IMM || code->op == FETCH_OP_COMM || code->op == FETCH_OP_DATA) || code->op == FETCH_OP_TP_ARG || parg->count) { /* @@ -679,6 +691,8 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size, * must be kept, and if parg->count != 0, this is an * array of string pointers instead of string address * itself. + * For the symstr, it doesn't need to dereference, thus + * it just get the value. */ code++; if (code->op != FETCH_OP_NOP) { @@ -690,6 +704,8 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size, if (!strcmp(parg->type->name, "ustring") || code->op == FETCH_OP_UDEREF) code->op = FETCH_OP_ST_USTRING; + else if (!strcmp(parg->type->name, "symstr")) + code->op = FETCH_OP_ST_SYMSTR; else code->op = FETCH_OP_ST_STRING; code->size = parg->type->size; @@ -919,8 +935,7 @@ static int __set_print_fmt(struct trace_probe *tp, char *buf, int len, for (i = 0; i < tp->nr_args; i++) { parg = tp->args + i; if (parg->count) { - if ((strcmp(parg->type->name, "string") == 0) || - (strcmp(parg->type->name, "ustring") == 0)) + if (parg->type->is_string) fmt = ", __get_str(%s[%d])"; else fmt = ", REC->%s[%d]"; @@ -928,8 +943,7 @@ static int __set_print_fmt(struct trace_probe *tp, char *buf, int len, pos += snprintf(buf + pos, LEN_OR_ZERO, fmt, parg->name, j); } else { - if ((strcmp(parg->type->name, "string") == 0) || - (strcmp(parg->type->name, "ustring") == 0)) + if (parg->type->is_string) fmt = ", __get_str(%s)"; else fmt = ", REC->%s"; diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h index de38f1c03776..0838b74f403b 100644 --- a/kernel/trace/trace_probe.h +++ b/kernel/trace/trace_probe.h @@ -98,6 +98,7 @@ enum fetch_op { FETCH_OP_ST_UMEM, /* Mem: .offset, .size */ FETCH_OP_ST_STRING, /* String: .offset, .size */ FETCH_OP_ST_USTRING, /* User String: .offset, .size */ + FETCH_OP_ST_SYMSTR, /* Kernel Symbol String: .offset, .size */ // Stage 4 (modify) op FETCH_OP_MOD_BF, /* Bitfield: .basesize, .lshift, .rshift */ // Stage 5 (loop) op @@ -133,7 +134,8 @@ struct fetch_insn { struct fetch_type { const char *name; /* Name of type */ size_t size; /* Byte size of type */ - int is_signed; /* Signed flag */ + bool is_signed; /* Signed flag */ + bool is_string; /* String flag */ print_type_func_t print; /* Print functions */ const char *fmt; /* Format string */ const char *fmttype; /* Name in format file */ @@ -177,16 +179,19 @@ DECLARE_BASIC_PRINT_TYPE_FUNC(symbol); #define _ADDR_FETCH_TYPE(t) __ADDR_FETCH_TYPE(t) #define ADDR_FETCH_TYPE _ADDR_FETCH_TYPE(BITS_PER_LONG) -#define __ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, _fmttype) \ - {.name = _name, \ +#define __ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, str, _fmttype) \ + {.name = _name, \ .size = _size, \ - .is_signed = sign, \ + .is_signed = (bool)sign, \ + .is_string = (bool)str, \ .print = PRINT_TYPE_FUNC_NAME(ptype), \ .fmt = PRINT_TYPE_FMT_NAME(ptype), \ .fmttype = _fmttype, \ } + +/* Non string types can use these macros */ #define _ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, _fmttype) \ - __ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, #_fmttype) + __ASSIGN_FETCH_TYPE(_name, ptype, ftype, _size, sign, 0, #_fmttype) #define ASSIGN_FETCH_TYPE(ptype, ftype, sign) \ _ASSIGN_FETCH_TYPE(#ptype, ptype, ftype, sizeof(ftype), sign, ptype) @@ -431,6 +436,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call, C(ARRAY_TOO_BIG, "Array number is too big"), \ C(BAD_TYPE, "Unknown type is specified"), \ C(BAD_STRING, "String accepts only memory argument"), \ + C(BAD_SYMSTRING, "Symbol String doesn't accept data/userdata"), \ C(BAD_BITFIELD, "Invalid bitfield"), \ C(ARG_NAME_TOO_LONG, "Argument name is too long"), \ C(NO_ARG_NAME, "Argument name is not specified"), \ diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h index b3bdb8ddb862..5cea672243f6 100644 --- a/kernel/trace/trace_probe_tmpl.h +++ b/kernel/trace/trace_probe_tmpl.h @@ -67,6 +67,37 @@ probe_mem_read(void *dest, void *src, size_t size); static nokprobe_inline int probe_mem_read_user(void *dest, void *src, size_t size); +static nokprobe_inline int +fetch_store_symstrlen(unsigned long addr) +{ + char namebuf[KSYM_SYMBOL_LEN]; + int ret; + + ret = sprint_symbol(namebuf, addr); + if (ret < 0) + return 0; + + return ret + 1; +} + +/* + * Fetch a null-terminated symbol string + offset. Caller MUST set *(u32 *)buf + * with max length and relative data location. + */ +static nokprobe_inline int +fetch_store_symstring(unsigned long addr, void *dest, void *base) +{ + int maxlen = get_loc_len(*(u32 *)dest); + void *__dest; + + if (unlikely(!maxlen)) + return -ENOMEM; + + __dest = get_loc_data(dest, base); + + return sprint_symbol(__dest, addr); +} + /* From the 2nd stage, routine is same */ static nokprobe_inline int process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val, @@ -99,16 +130,22 @@ stage2: stage3: /* 3rd stage: store value to buffer */ if (unlikely(!dest)) { - if (code->op == FETCH_OP_ST_STRING) { + switch (code->op) { + case FETCH_OP_ST_STRING: ret = fetch_store_strlen(val + code->offset); code++; goto array; - } else if (code->op == FETCH_OP_ST_USTRING) { + case FETCH_OP_ST_USTRING: ret += fetch_store_strlen_user(val + code->offset); code++; goto array; - } else + case FETCH_OP_ST_SYMSTR: + ret += fetch_store_symstrlen(val + code->offset); + code++; + goto array; + default: return -EILSEQ; + } } switch (code->op) { @@ -129,6 +166,10 @@ stage3: loc = *(u32 *)dest; ret = fetch_store_string_user(val + code->offset, dest, base); break; + case FETCH_OP_ST_SYMSTR: + loc = *(u32 *)dest; + ret = fetch_store_symstring(val + code->offset, dest, base); + break; default: return -EILSEQ; } -- cgit v1.2.3