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Commit 4ca53085 authored by Steven Rostedt's avatar Steven Rostedt
Browse files

tracing: protect reader of cmdline output 



Impact: fix to one cause of incorrect comm outputs in trace

The spinlock only protected the creation of a comm <=> pid pair.
But it was possible that a reader could look up a pid, and get the
wrong comm because it had no locking.

This also required changing trace_find_cmdline to copy the comm cache
and not just send back a pointer to it.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
parent 03303549

kernel/trace/blktrace.c

+18 −5
Original line number Diff line number Diff line
@@ -1027,7 +1027,9 @@ static int blk_log_action_seq(struct trace_seq *s, const struct blk_io_trace *t, 


static int blk_log_generic(struct trace_seq *s, const struct trace_entry *ent)

{

	const char *cmd = trace_find_cmdline(ent->pid);

	char cmd[TASK_COMM_LEN];



	trace_find_cmdline(ent->pid, cmd);



	if (t_sec(ent))

		return trace_seq_printf(s, "%llu + %u [%s]\n",
@@ -1057,19 +1059,30 @@ static int blk_log_remap(struct trace_seq *s, const struct trace_entry *ent) 


static int blk_log_plug(struct trace_seq *s, const struct trace_entry *ent)

{

	return trace_seq_printf(s, "[%s]\n", trace_find_cmdline(ent->pid));

	char cmd[TASK_COMM_LEN];



	trace_find_cmdline(ent->pid, cmd);



	return trace_seq_printf(s, "[%s]\n", cmd);

}



static int blk_log_unplug(struct trace_seq *s, const struct trace_entry *ent)

{

	return trace_seq_printf(s, "[%s] %llu\n", trace_find_cmdline(ent->pid),

				get_pdu_int(ent));

	char cmd[TASK_COMM_LEN];



	trace_find_cmdline(ent->pid, cmd);



	return trace_seq_printf(s, "[%s] %llu\n", cmd, get_pdu_int(ent));

}



static int blk_log_split(struct trace_seq *s, const struct trace_entry *ent)

{

	char cmd[TASK_COMM_LEN];



	trace_find_cmdline(ent->pid, cmd);



	return trace_seq_printf(s, "%llu / %llu [%s]\n", t_sector(ent),

				get_pdu_int(ent), trace_find_cmdline(ent->pid));

				get_pdu_int(ent), cmd);

}



/*

kernel/trace/trace.c

+12 −8
Original line number Diff line number Diff line
@@ -770,25 +770,29 @@ static void trace_save_cmdline(struct task_struct *tsk) 
	__raw_spin_unlock(&trace_cmdline_lock);

}



char *trace_find_cmdline(int pid)

void trace_find_cmdline(int pid, char comm[])

{

	char *cmdline = "<...>";

	unsigned map;



	if (!pid)

		return "<idle>";

	if (!pid) {

		strcpy(comm, "<idle>");

		return;

	}



	if (pid > PID_MAX_DEFAULT)

		goto out;

	if (pid > PID_MAX_DEFAULT) {

		strcpy(comm, "<...>");

		return;

	}



	__raw_spin_lock(&trace_cmdline_lock);

	map = map_pid_to_cmdline[pid];

	if (map >= SAVED_CMDLINES)

		goto out;



	cmdline = saved_cmdlines[map];

	strcpy(comm, saved_cmdlines[map]);



 out:

	return cmdline;

	__raw_spin_unlock(&trace_cmdline_lock);

}



void tracing_record_cmdline(struct task_struct *tsk)

kernel/trace/trace.h

+1 −1
Original line number Diff line number Diff line
@@ -547,7 +547,7 @@ struct tracer_switch_ops { 
};

#endif /* CONFIG_CONTEXT_SWITCH_TRACER */



extern char *trace_find_cmdline(int pid);

extern void trace_find_cmdline(int pid, char comm[]);



#ifdef CONFIG_DYNAMIC_FTRACE

extern unsigned long ftrace_update_tot_cnt;

kernel/trace/trace_functions_graph.c

+6 −6
Original line number Diff line number Diff line
@@ -190,15 +190,15 @@ print_graph_cpu(struct trace_seq *s, int cpu) 
static enum print_line_t

print_graph_proc(struct trace_seq *s, pid_t pid)

{

	int i;

	int ret;

	int len;

	char comm[8];

	int spaces = 0;

	char comm[TASK_COMM_LEN];

	/* sign + log10(MAX_INT) + '\0' */

	char pid_str[11];

	int spaces = 0;

	int ret;

	int len;

	int i;



	strncpy(comm, trace_find_cmdline(pid), 7);

	trace_find_cmdline(pid, comm);

	comm[7] = '\0';

	sprintf(pid_str, "%d", pid);

kernel/trace/trace_output.c

+12 −6
Original line number Diff line number Diff line
@@ -309,9 +309,9 @@ static int 
lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)

{

	int hardirq, softirq;

	char *comm;

	char comm[TASK_COMM_LEN];



	comm = trace_find_cmdline(entry->pid);

	trace_find_cmdline(entry->pid, comm);

	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;

	softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
@@ -346,10 +346,12 @@ int trace_print_context(struct trace_iterator *iter) 
{

	struct trace_seq *s = &iter->seq;

	struct trace_entry *entry = iter->ent;

	char *comm = trace_find_cmdline(entry->pid);

	unsigned long long t = ns2usecs(iter->ts);

	unsigned long usec_rem = do_div(t, USEC_PER_SEC);

	unsigned long secs = (unsigned long)t;

	char comm[TASK_COMM_LEN];



	trace_find_cmdline(entry->pid, comm);



	return trace_seq_printf(s, "%16s-%-5d [%03d] %5lu.%06lu: ",

				comm, entry->pid, iter->cpu, secs, usec_rem);
@@ -372,7 +374,10 @@ int trace_print_lat_context(struct trace_iterator *iter) 
	rel_usecs = ns2usecs(next_ts - iter->ts);



	if (verbose) {

		char *comm = trace_find_cmdline(entry->pid);

		char comm[TASK_COMM_LEN];



		trace_find_cmdline(entry->pid, comm);



		ret = trace_seq_printf(s, "%16s %5d %3d %d %08x %08lx [%08lx]"

				       " %ld.%03ldms (+%ld.%03ldms): ", comm,

				       entry->pid, iter->cpu, entry->flags,
@@ -577,14 +582,15 @@ static enum print_line_t trace_ctxwake_print(struct trace_iterator *iter, 
					     char *delim)

{

	struct ctx_switch_entry *field;

	char *comm;

	char comm[TASK_COMM_LEN];

	int S, T;





	trace_assign_type(field, iter->ent);



	T = task_state_char(field->next_state);

	S = task_state_char(field->prev_state);

	comm = trace_find_cmdline(field->next_pid);

	trace_find_cmdline(field->next_pid, comm);

	if (!trace_seq_printf(&iter->seq,

			      " %5d:%3d:%c %s [%03d] %5d:%3d:%c %s\n",

			      field->prev_pid,