Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread pointer

From: Chao Yu
Date: Thu Apr 26 2018 - 22:05:00 EST

Next message: Chao Yu: "Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread pointer"
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In reply to: Jaegeuk Kim: "Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread pointer"
Next in thread: Chao Yu: "Re: [PATCH v2] f2fs: fix to avoid race during access gc_thread pointer"
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On 2018/4/27 0:03, Jaegeuk Kim wrote:
> 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

Better,

> issue_discard_thread?

There is more cases can be called from different scenarios:
- select_policy()
- need_SSR()

Thanks,

>
>>
>> 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@xxxxxxxxxx>
>> ---
>> 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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