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Date: Thu, 26 Apr 2018 10:03:59 -0600
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread
pointer
On 04/24, Chao Yu wrote:
> 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.
Do we just need to check &sb->s_umount in f2fs_sbi_store() and
issue_discard_thread?
>
> 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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