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

From: Chao Yu
Date: Thu Apr 26 2018 - 22:07:25 EST

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On 2018/4/27 10:04, Chao Yu wrote:
> 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()

BTW, do you agree with introducing {init,destroy}_gc_context as the patch does?

Thanks,

>
> 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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