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Commit e1105c64 authored by Paul Burton's avatar Paul Burton Committed by Greg Kroah-Hartman
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tracing: Resize tgid_map to pid_max, not PID_MAX_DEFAULT 

commit 4030a6e6a6a4a42ff8c18414c9e0c93e24cc70b8 upstream.

Currently tgid_map is sized at PID_MAX_DEFAULT entries, which means that
on systems where pid_max is configured higher than PID_MAX_DEFAULT the
ftrace record-tgid option doesn't work so well. Any tasks with PIDs
higher than PID_MAX_DEFAULT are simply not recorded in tgid_map, and
don't show up in the saved_tgids file.

In particular since systemd v243 & above configure pid_max to its
highest possible 1<<22 value by default on 64 bit systems this renders
the record-tgids option of little use.

Increase the size of tgid_map to the configured pid_max instead,
allowing it to cover the full range of PIDs up to the maximum value of
PID_MAX_LIMIT if the system is configured that way.

On 64 bit systems with pid_max == PID_MAX_LIMIT this will increase the
size of tgid_map from 256KiB to 16MiB. Whilst this 64x increase in
memory overhead sounds significant 64 bit systems are presumably best
placed to accommodate it, and since tgid_map is only allocated when the
record-tgid option is actually used presumably the user would rather it
spends sufficient memory to actually record the tgids they expect.

The size of tgid_map could also increase for CONFIG_BASE_SMALL=y
configurations, but these seem unlikely to be systems upon which people
are both configuring a large pid_max and running ftrace with record-tgid
anyway.

Of note is that we only allocate tgid_map once, the first time that the
record-tgid option is enabled. Therefore its size is only set once, to
the value of pid_max at the time the record-tgid option is first
enabled. If a user increases pid_max after that point, the saved_tgids
file will not contain entries for any tasks with pids beyond the earlier
value of pid_max.

Link: https://lkml.kernel.org/r/20210701172407.889626-2-paulburton@google.com



Fixes: d914ba37 ("tracing: Add support for recording tgid of tasks")
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarPaul Burton <paulburton@google.com>
[ Fixed comment coding style ]
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 44896b31

kernel/trace/trace.c

+47 −16
Original line number Diff line number Diff line
@@ -1729,8 +1729,15 @@ void tracing_reset_all_online_cpus(void) 
	}

}



/*

 * The tgid_map array maps from pid to tgid; i.e. the value stored at index i

 * is the tgid last observed corresponding to pid=i.

 */

static int *tgid_map;



/* The maximum valid index into tgid_map. */

static size_t tgid_map_max;



#define SAVED_CMDLINES_DEFAULT 128

#define NO_CMDLINE_MAP UINT_MAX

static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED;
@@ -2003,24 +2010,41 @@ void trace_find_cmdline(int pid, char comm[]) 
	preempt_enable();

}



static int *trace_find_tgid_ptr(int pid)

{

	/*

	 * Pairs with the smp_store_release in set_tracer_flag() to ensure that

	 * if we observe a non-NULL tgid_map then we also observe the correct

	 * tgid_map_max.

	 */

	int *map = smp_load_acquire(&tgid_map);



	if (unlikely(!map || pid > tgid_map_max))

		return NULL;



	return &map[pid];

}



int trace_find_tgid(int pid)

{

	if (unlikely(!tgid_map || !pid || pid > PID_MAX_DEFAULT))

		return 0;

	int *ptr = trace_find_tgid_ptr(pid);



	return tgid_map[pid];

	return ptr ? *ptr : 0;

}



static int trace_save_tgid(struct task_struct *tsk)

{

	int *ptr;



	/* treat recording of idle task as a success */

	if (!tsk->pid)

		return 1;



	if (unlikely(!tgid_map || tsk->pid > PID_MAX_DEFAULT))

	ptr = trace_find_tgid_ptr(tsk->pid);

	if (!ptr)

		return 0;



	tgid_map[tsk->pid] = tsk->tgid;

	*ptr = tsk->tgid;

	return 1;

}
@@ -4355,6 +4379,8 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set) 


int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)

{

	int *map;



	if ((mask == TRACE_ITER_RECORD_TGID) ||

	    (mask == TRACE_ITER_RECORD_CMD))

		lockdep_assert_held(&event_mutex);
@@ -4377,10 +4403,19 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled) 
		trace_event_enable_cmd_record(enabled);



	if (mask == TRACE_ITER_RECORD_TGID) {

		if (!tgid_map)

			tgid_map = kvcalloc(PID_MAX_DEFAULT + 1,

					   sizeof(*tgid_map),

		if (!tgid_map) {

			tgid_map_max = pid_max;

			map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map),

				       GFP_KERNEL);



			/*

			 * Pairs with smp_load_acquire() in

			 * trace_find_tgid_ptr() to ensure that if it observes

			 * the tgid_map we just allocated then it also observes

			 * the corresponding tgid_map_max value.

			 */

			smp_store_release(&tgid_map, map);

		}

		if (!tgid_map) {

			tr->trace_flags &= ~TRACE_ITER_RECORD_TGID;

			return -ENOMEM;
@@ -4754,18 +4789,14 @@ static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos) 
{

	int pid = ++(*pos);



	if (pid > PID_MAX_DEFAULT)

		return NULL;



	return &tgid_map[pid];

	return trace_find_tgid_ptr(pid);

}



static void *saved_tgids_start(struct seq_file *m, loff_t *pos)

{

	if (!tgid_map || *pos > PID_MAX_DEFAULT)

		return NULL;

	int pid = *pos;



	return &tgid_map[*pos];

	return trace_find_tgid_ptr(pid);

}



static void saved_tgids_stop(struct seq_file *m, void *v)