Commit 0eb96701 authored by Abhishek Sagar's avatar Abhishek Sagar Committed by Ingo Molnar
Browse files

ftrace: prevent freeing of all failed updates 



Prevent freeing of records which cause problems and correspond to function from
core kernel text. A new flag, FTRACE_FL_CONVERTED is used to mark a record
as "converted". All other records are patched lazily to NOPs. Failed records
now also remain on frace_hash table. Each invocation of ftrace_record_ip now
checks whether the traced function has ever been recorded (including past
failures) and doesn't re-record it again.

Signed-off-by: default avatarAbhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e0773410

include/linux/ftrace.h

+1 −0
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ enum { 
	FTRACE_FL_FILTER	= (1 << 2),

	FTRACE_FL_ENABLED	= (1 << 3),

	FTRACE_FL_NOTRACE	= (1 << 4),

	FTRACE_FL_CONVERTED	= (1 << 5),

};



struct dyn_ftrace {

kernel/trace/ftrace.c

+46 −30
Original line number Diff line number Diff line
@@ -216,6 +216,12 @@ ftrace_add_hash(struct dyn_ftrace *node, unsigned long key) 
	hlist_add_head_rcu(&node->node, &ftrace_hash[key]);

}



/* called from kstop_machine */

static inline void ftrace_del_hash(struct dyn_ftrace *node)

{

	hlist_del(&node->node);

}



static void ftrace_free_rec(struct dyn_ftrace *rec)

{

	/* no locking, only called from kstop_machine */
@@ -332,12 +338,11 @@ ftrace_record_ip(unsigned long ip) 
#define FTRACE_ADDR ((long)(ftrace_caller))

#define MCOUNT_ADDR ((long)(mcount))



static void

static int

__ftrace_replace_code(struct dyn_ftrace *rec,

		      unsigned char *old, unsigned char *new, int enable)

{

	unsigned long ip, fl;

	int failed;



	ip = rec->ip;
@@ -364,7 +369,7 @@ __ftrace_replace_code(struct dyn_ftrace *rec, 


		if ((fl ==  (FTRACE_FL_FILTER | FTRACE_FL_ENABLED)) ||

		    (fl == 0) || (rec->flags & FTRACE_FL_NOTRACE))

			return;

			return 0;



		/*

		 * If it is enabled disable it,
@@ -388,7 +393,7 @@ __ftrace_replace_code(struct dyn_ftrace *rec, 
			 */

			fl = rec->flags & (FTRACE_FL_NOTRACE | FTRACE_FL_ENABLED);

			if (fl == FTRACE_FL_NOTRACE)

				return;

				return 0;



			new = ftrace_call_replace(ip, FTRACE_ADDR);

		} else
@@ -396,34 +401,24 @@ __ftrace_replace_code(struct dyn_ftrace *rec, 


		if (enable) {

			if (rec->flags & FTRACE_FL_ENABLED)

				return;

				return 0;

			rec->flags |= FTRACE_FL_ENABLED;

		} else {

			if (!(rec->flags & FTRACE_FL_ENABLED))

				return;

				return 0;

			rec->flags &= ~FTRACE_FL_ENABLED;

		}

	}



	failed = ftrace_modify_code(ip, old, new);

	if (failed) {

		unsigned long key;

		/* It is possible that the function hasn't been converted yet */

		key = hash_long(ip, FTRACE_HASHBITS);

		if (!ftrace_ip_in_hash(ip, key)) {

			rec->flags |= FTRACE_FL_FAILED;

			ftrace_free_rec(rec);

		}



	}

	return ftrace_modify_code(ip, old, new);

}



static void ftrace_replace_code(int enable)

{

	int i, failed;

	unsigned char *new = NULL, *old = NULL;

	struct dyn_ftrace *rec;

	struct ftrace_page *pg;

	int i;



	if (enable)

		old = ftrace_nop_replace();
@@ -438,7 +433,15 @@ static void ftrace_replace_code(int enable) 
			if (rec->flags & FTRACE_FL_FAILED)

				continue;



			__ftrace_replace_code(rec, old, new, enable);

			failed = __ftrace_replace_code(rec, old, new, enable);

			if (failed && (rec->flags & FTRACE_FL_CONVERTED)) {

				rec->flags |= FTRACE_FL_FAILED;

				if ((system_state == SYSTEM_BOOTING) ||

				    !kernel_text_address(rec->ip)) {

					ftrace_del_hash(rec);

					ftrace_free_rec(rec);

				}

			}

		}

	}

}
@@ -467,7 +470,6 @@ ftrace_code_disable(struct dyn_ftrace *rec) 
	failed = ftrace_modify_code(ip, call, nop);

	if (failed) {

		rec->flags |= FTRACE_FL_FAILED;

		ftrace_free_rec(rec);

		return 0;

	}

	return 1;
@@ -621,8 +623,7 @@ unsigned long ftrace_update_tot_cnt; 
static int __ftrace_update_code(void *ignore)

{

	struct dyn_ftrace *p;

	struct hlist_head head;

	struct hlist_node *t;

	struct hlist_node *t, *n;

	int save_ftrace_enabled;

	cycle_t start, stop;

	int i;
@@ -637,19 +638,34 @@ static int __ftrace_update_code(void *ignore) 


	/* No locks needed, the machine is stopped! */

	for (i = 0; i < FTRACE_HASHSIZE; i++) {

		if (hlist_empty(&ftrace_hash[i]))

		/* all CPUS are stopped, we are safe to modify code */

		hlist_for_each_entry_safe(p, t, n, &ftrace_hash[i], node) {

			/* Skip over failed records which have not been

			 * freed. */

			if (p->flags & FTRACE_FL_FAILED)

				continue;



		head = ftrace_hash[i];

		INIT_HLIST_HEAD(&ftrace_hash[i]);

			/* Unconverted records are always at the head of the

			 * hash bucket. Once we encounter a converted record,

			 * simply skip over to the next bucket. Saves ftraced

			 * some processor cycles (ftrace does its bid for

			 * global warming :-p ). */

			if (p->flags & (FTRACE_FL_CONVERTED))

				break;



		/* all CPUS are stopped, we are safe to modify code */

		hlist_for_each_entry(p, t, &head, node) {

			if (ftrace_code_disable(p))

			if (ftrace_code_disable(p)) {

				p->flags |= FTRACE_FL_CONVERTED;

				ftrace_update_cnt++;

		}

			} else {

				if ((system_state == SYSTEM_BOOTING) ||

				    !kernel_text_address(p->ip)) {

					ftrace_del_hash(p);

					ftrace_free_rec(p);



				}

			}

		}

	}



	stop = ftrace_now(raw_smp_processor_id());

	ftrace_update_time = stop - start;

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