Message-ID: <20180424024214.83177-1-yuchao0@huawei.com>
Date:   Tue, 24 Apr 2018 10:42:14 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>,
        Chao Yu <yuchao0@...wei.com>
Subject: [PATCH v2] f2fs: fix to avoid race during access gc_thread pointer

Thread A			Thread B		Thread C
- f2fs_remount
 - stop_gc_thread
				- f2fs_sbi_store
							- issue_discard_thread
   sbi->gc_thread = NULL;
				  sbi->gc_thread->gc_wake = 1
							  access sbi->gc_thread->gc_urgent

Previously, we allocate memory for sbi->gc_thread based on background
gc thread mount option, the memory can be released if we turn off
that mount option, but still there are several places access gc_thread
pointer without considering race condition, result in NULL point
dereference.

In order to fix this issue, keep gc_thread structure valid in sbi all
the time instead of alloc/free it dynamically.

In addition, add a rw semaphore to exclude rw operation in fields of
gc_thread.

Signed-off-by: Chao Yu <yuchao0@...wei.com>
---
v2:
- add a rw semaphore to exclude rw operation suggested by Jaegeuk.
 fs/f2fs/debug.c   |  3 +--
 fs/f2fs/f2fs.h    |  9 ++++++-
 fs/f2fs/gc.c      | 78 ++++++++++++++++++++++++++++++++++++-------------------
 fs/f2fs/gc.h      |  1 +
 fs/f2fs/segment.c | 10 +++++--
 fs/f2fs/super.c   | 26 +++++++++++++------
 fs/f2fs/sysfs.c   | 26 ++++++++++++++-----
 7 files changed, 107 insertions(+), 46 deletions(-)

diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index a66107b5cfff..0fbd674c66fb 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -221,8 +221,7 @@ static void update_mem_info(struct f2fs_sb_info *sbi)
 	si->cache_mem = 0;
 
 	/* build gc */
-	if (sbi->gc_thread)
-		si->cache_mem += sizeof(struct f2fs_gc_kthread);
+	si->cache_mem += sizeof(struct f2fs_gc_kthread);
 
 	/* build merge flush thread */
 	if (SM_I(sbi)->fcc_info)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 8f3ad9662d13..75d3b4875429 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1412,6 +1412,11 @@ static inline struct sit_info *SIT_I(struct f2fs_sb_info *sbi)
 	return (struct sit_info *)(SM_I(sbi)->sit_info);
 }
 
+static inline struct f2fs_gc_kthread *GC_I(struct f2fs_sb_info *sbi)
+{
+	return (struct f2fs_gc_kthread *)(sbi->gc_thread);
+}
+
 static inline struct free_segmap_info *FREE_I(struct f2fs_sb_info *sbi)
 {
 	return (struct free_segmap_info *)(SM_I(sbi)->free_info);
@@ -2954,8 +2959,10 @@ bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len);
 /*
  * gc.c
  */
+int init_gc_context(struct f2fs_sb_info *sbi);
+void destroy_gc_context(struct f2fs_sb_info * sbi);
 int start_gc_thread(struct f2fs_sb_info *sbi);
-void stop_gc_thread(struct f2fs_sb_info *sbi);
+bool stop_gc_thread(struct f2fs_sb_info *sbi);
 block_t start_bidx_of_node(unsigned int node_ofs, struct inode *inode);
 int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background,
 			unsigned int segno);
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 70418b34c5f6..2febb84b2fd6 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -26,8 +26,8 @@
 static int gc_thread_func(void *data)
 {
 	struct f2fs_sb_info *sbi = data;
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
-	wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
+	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
+	wait_queue_head_t *wq = &gc_th->gc_wait_queue_head;
 	unsigned int wait_ms;
 
 	wait_ms = gc_th->min_sleep_time;
@@ -114,17 +114,15 @@ static int gc_thread_func(void *data)
 	return 0;
 }
 
-int start_gc_thread(struct f2fs_sb_info *sbi)
+int init_gc_context(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_gc_kthread *gc_th;
-	dev_t dev = sbi->sb->s_bdev->bd_dev;
-	int err = 0;
 
 	gc_th = f2fs_kmalloc(sbi, sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
-	if (!gc_th) {
-		err = -ENOMEM;
-		goto out;
-	}
+	if (!gc_th)
+		return -ENOMEM;
+
+	gc_th->f2fs_gc_task = NULL;
 
 	gc_th->urgent_sleep_time = DEF_GC_THREAD_URGENT_SLEEP_TIME;
 	gc_th->min_sleep_time = DEF_GC_THREAD_MIN_SLEEP_TIME;
@@ -135,35 +133,59 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
 	gc_th->gc_urgent = 0;
 	gc_th->gc_wake= 0;
 
+	init_rwsem(&gc_th->gc_rwsem);
+
 	sbi->gc_thread = gc_th;
-	init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
-	sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
+
+	return 0;
+}
+
+void destroy_gc_context(struct f2fs_sb_info *sbi)
+{
+	kfree(GC_I(sbi));
+	sbi->gc_thread = NULL;
+}
+
+int start_gc_thread(struct f2fs_sb_info *sbi)
+{
+	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
+	dev_t dev = sbi->sb->s_bdev->bd_dev;
+	int err = 0;
+
+	init_waitqueue_head(&gc_th->gc_wait_queue_head);
+	gc_th->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
 			"f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
 	if (IS_ERR(gc_th->f2fs_gc_task)) {
 		err = PTR_ERR(gc_th->f2fs_gc_task);
-		kfree(gc_th);
-		sbi->gc_thread = NULL;
+		gc_th->f2fs_gc_task = NULL;
 	}
-out:
+
 	return err;
 }
 
-void stop_gc_thread(struct f2fs_sb_info *sbi)
+bool stop_gc_thread(struct f2fs_sb_info *sbi)
 {
-	struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
-	if (!gc_th)
-		return;
-	kthread_stop(gc_th->f2fs_gc_task);
-	kfree(gc_th);
-	sbi->gc_thread = NULL;
+	struct f2fs_gc_kthread *gc_th = GC_I(sbi);
+	bool stopped = false;
+
+	down_write(&gc_th->gc_rwsem);
+	if (gc_th->f2fs_gc_task) {
+		kthread_stop(gc_th->f2fs_gc_task);
+		gc_th->f2fs_gc_task = NULL;
+		stopped = true;
+	}
+	up_write(&gc_th->gc_rwsem);
+
+	return stopped;
 }
 
 static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
 {
 	int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
 
-	if (!gc_th)
-		return gc_mode;
+	down_read(&gc_th->gc_rwsem);
+	if (!gc_th->f2fs_gc_task)
+		goto out;
 
 	if (gc_th->gc_idle) {
 		if (gc_th->gc_idle == 1)
@@ -173,6 +195,8 @@ static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
 	}
 	if (gc_th->gc_urgent)
 		gc_mode = GC_GREEDY;
+out:
+	up_read(&gc_th->gc_rwsem);
 	return gc_mode;
 }
 
@@ -187,17 +211,19 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
 		p->max_search = dirty_i->nr_dirty[type];
 		p->ofs_unit = 1;
 	} else {
-		p->gc_mode = select_gc_type(sbi->gc_thread, gc_type);
+		p->gc_mode = select_gc_type(GC_I(sbi), gc_type);
 		p->dirty_segmap = dirty_i->dirty_segmap[DIRTY];
 		p->max_search = dirty_i->nr_dirty[DIRTY];
 		p->ofs_unit = sbi->segs_per_sec;
 	}
 
 	/* we need to check every dirty segments in the FG_GC case */
-	if (gc_type != FG_GC &&
-			(sbi->gc_thread && !sbi->gc_thread->gc_urgent) &&
+	down_read(&GC_I(sbi)->gc_rwsem);
+	if (gc_type != FG_GC && GC_I(sbi)->f2fs_gc_task &&
+			!GC_I(sbi)->gc_urgent &&
 			p->max_search > sbi->max_victim_search)
 		p->max_search = sbi->max_victim_search;
+	up_read(&GC_I(sbi)->gc_rwsem);
 
 	/* let's select beginning hot/small space first in no_heap mode*/
 	if (test_opt(sbi, NOHEAP) &&
diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
index b0045d4c8d1e..9a5b273328c2 100644
--- a/fs/f2fs/gc.h
+++ b/fs/f2fs/gc.h
@@ -26,6 +26,7 @@
 #define DEF_MAX_VICTIM_SEARCH 4096 /* covers 8GB */
 
 struct f2fs_gc_kthread {
+	struct rw_semaphore gc_rwsem;		/* semaphore for f2fs_gc_task */
 	struct task_struct *f2fs_gc_task;
 	wait_queue_head_t gc_wait_queue_head;
 
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 5960768d26df..f787eea1b2f6 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -177,8 +177,12 @@ bool need_SSR(struct f2fs_sb_info *sbi)
 
 	if (test_opt(sbi, LFS))
 		return false;
-	if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
+	down_read(&GC_I(sbi)->gc_rwsem);
+	if (GC_I(sbi)->f2fs_gc_task && GC_I(sbi)->gc_urgent) {
+		down_read(&GC_I(sbi)->gc_rwsem);
 		return true;
+	}
+	up_read(&GC_I(sbi)->gc_rwsem);
 
 	return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
 			SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
@@ -1425,8 +1429,10 @@ static int issue_discard_thread(void *data)
 		if (dcc->discard_wake)
 			dcc->discard_wake = 0;
 
-		if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
+		down_read(&GC_I(sbi)->gc_rwsem);
+		if (GC_I(sbi)->f2fs_gc_task && GC_I(sbi)->gc_urgent)
 			init_discard_policy(&dpolicy, DPOLICY_FORCE, 1);
+		up_read(&GC_I(sbi)->gc_rwsem);
 
 		sb_start_intwrite(sbi->sb);
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index dedb8e50b440..199f29dce86d 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1044,6 +1044,7 @@ static void f2fs_put_super(struct super_block *sb)
 	kfree(sbi->raw_super);
 
 	destroy_device_list(sbi);
+	destroy_gc_context(sbi);
 	mempool_destroy(sbi->write_io_dummy);
 #ifdef CONFIG_QUOTA
 	for (i = 0; i < MAXQUOTAS; i++)
@@ -1476,15 +1477,18 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	 * option. Also sync the filesystem.
 	 */
 	if ((*flags & SB_RDONLY) || !test_opt(sbi, BG_GC)) {
-		if (sbi->gc_thread) {
-			stop_gc_thread(sbi);
-			need_restart_gc = true;
+		need_restart_gc = stop_gc_thread(sbi);
+	} else {
+		down_write(&GC_I(sbi)->gc_rwsem);
+		if (!GC_I(sbi)->f2fs_gc_task) {
+			err = start_gc_thread(sbi);
+			if (err) {
+				up_write(&GC_I(sbi)->gc_rwsem);
+				goto restore_opts;
+			}
+			need_stop_gc = true;
 		}
-	} else if (!sbi->gc_thread) {
-		err = start_gc_thread(sbi);
-		if (err)
-			goto restore_opts;
-		need_stop_gc = true;
+		up_write(&GC_I(sbi)->gc_rwsem);
 	}
 
 	if (*flags & SB_RDONLY ||
@@ -2771,6 +2775,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 		goto free_meta_inode;
 	}
 
+	err = init_gc_context(sbi);
+	if (err)
+		goto free_checkpoint;
+
 	/* Initialize device list */
 	err = f2fs_scan_devices(sbi);
 	if (err) {
@@ -2981,6 +2989,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	destroy_segment_manager(sbi);
 free_devices:
 	destroy_device_list(sbi);
+	destroy_gc_context(sbi);
+free_checkpoint:
 	kfree(sbi->ckpt);
 free_meta_inode:
 	make_bad_inode(sbi->meta_inode);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 2c53de9251be..b8d09935e43f 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -46,7 +46,7 @@ struct f2fs_attr {
 static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
 {
 	if (struct_type == GC_THREAD)
-		return (unsigned char *)sbi->gc_thread;
+		return (unsigned char *)GC_I(sbi);
 	else if (struct_type == SM_INFO)
 		return (unsigned char *)SM_I(sbi);
 	else if (struct_type == DCC_INFO)
@@ -248,16 +248,28 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
 	if (!strcmp(a->attr.name, "trim_sections"))
 		return -EINVAL;
 
-	*ui = t;
-
-	if (!strcmp(a->attr.name, "iostat_enable") && *ui == 0)
+	if (!strcmp(a->attr.name, "iostat_enable") && t == 0)
 		f2fs_reset_iostat(sbi);
-	if (!strcmp(a->attr.name, "gc_urgent") && t == 1 && sbi->gc_thread) {
-		sbi->gc_thread->gc_wake = 1;
-		wake_up_interruptible_all(&sbi->gc_thread->gc_wait_queue_head);
+
+	if (a->struct_type == GC_THREAD) {
+		down_write(&GC_I(sbi)->gc_rwsem);
+		if (!GC_I(sbi)->f2fs_gc_task) {
+			up_write(&GC_I(sbi)->gc_rwsem);
+			return -EINVAL;
+		}
+	}
+
+	if (!strcmp(a->attr.name, "gc_urgent") && t == 1) {
+		GC_I(sbi)->gc_wake = 1;
+		wake_up_interruptible_all(&GC_I(sbi)->gc_wait_queue_head);
 		wake_up_discard_thread(sbi, true);
 	}
 
+	*ui = t;
+
+	if (a->struct_type == GC_THREAD)
+		up_write(&GC_I(sbi)->gc_rwsem);
+
 	return count;
 }
 
-- 
2.15.0.55.gc2ece9dc4de6

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