Re: [PATCH 5/5] f2fs: fix to avoid race during access gc_thread pointer

From: Chao Yu
Date: Fri Apr 20 2018 - 03:26:07 EST

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In reply to: Jaegeuk Kim: "Re: [PATCH 5/5] f2fs: fix to avoid race during access gc_thread pointer"
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On 2018/4/20 11:54, Jaegeuk Kim wrote:
> On 04/20, Chao Yu wrote:
>> On 2018/4/20 11:19, Jaegeuk Kim wrote:
>>> On 04/18, 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
>>>
>>> Do we simply need a lock for this?
>>
>> Code will be more complicated for handling existed and new coming fields with
>> the sbi->gc_thread pointer, and causing unneeded lock overhead, right?
>>
>> So let's just allocate memory during fill_super?
>
> No, the case is when stopping the thread. We can keep the gc_thread and indicate
> its state as "disabled". Then, we need to handle other paths with the state?

After this patch, we use f2fs_gc_kthread.f2fs_gc_task to indicate whether GC
thread is existed, so you mean if we do that change, we also need to add a lock,
and access/update other fields in f2fs_gc_kthread after we check
f2fs_gc_kthread.f2fs_gc_task with a lock, right?

Like:

f2fs_sbi_store:

if (!strcmp(a->attr.name, "gc_urgent") && t == 1) {
gc_context_lock()
if (GC_I(sbi)->f2fs_gc_task) {
GC_I(sbi)->gc_wake = 1;
...
}
gc_context_unlock()

Do you mean that?

Thanks,

>
>>
>> Thanks,
>>
>>>
>>>>
>>>> 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.
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
>>>> ---
>>>> fs/f2fs/debug.c | 3 +--
>>>> fs/f2fs/f2fs.h | 7 +++++++
>>>> fs/f2fs/gc.c | 58 +++++++++++++++++++++++++++++++++----------------------
>>>> fs/f2fs/segment.c | 4 ++--
>>>> fs/f2fs/super.c | 13 +++++++++++--
>>>> fs/f2fs/sysfs.c | 8 ++++----
>>>> 6 files changed, 60 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
>>>> index 715beb85e9db..7bb036a3bb81 100644
>>>> --- a/fs/f2fs/debug.c
>>>> +++ b/fs/f2fs/debug.c
>>>> @@ -223,8 +223,7 @@ 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 567c6bb57ae3..c553f63199e8 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);
>>>> @@ -2954,6 +2959,8 @@ 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);
>>>> block_t start_bidx_of_node(unsigned int node_ofs, struct inode *inode);
>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>> index da89ca16a55d..7d310e454b77 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;
>>>> @@ -139,26 +137,41 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
>>>> gc_th->atomic_file[FG_GC] = 0;
>>>>
>>>> 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)
>>>> {
>>>> - 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);
>>>> +
>>>> + if (gc_th->f2fs_gc_task) {
>>>> + kthread_stop(gc_th->f2fs_gc_task);
>>>> + gc_th->f2fs_gc_task = NULL;
>>>> + }
>>>> }
>>>>
>>>> static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
>>>> @@ -190,15 +203,14 @@ 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) &&
>>>> + if (gc_type != FG_GC && !GC_I(sbi)->gc_urgent &&
>>>> p->max_search > sbi->max_victim_search)
>>>> p->max_search = sbi->max_victim_search;
>>>>
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 831cefa088bc..c869ce54be4d 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -177,7 +177,7 @@ bool need_SSR(struct f2fs_sb_info *sbi)
>>>>
>>>> if (test_opt(sbi, LFS))
>>>> return false;
>>>> - if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
>>>> + if (GC_I(sbi)->gc_urgent)
>>>> return true;
>>>>
>>>> return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
>>>> @@ -1422,7 +1422,7 @@ static int issue_discard_thread(void *data)
>>>> if (dcc->discard_wake)
>>>> dcc->discard_wake = 0;
>>>>
>>>> - if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
>>>> + if (GC_I(sbi)->gc_urgent)
>>>> init_discard_policy(&dpolicy, DPOLICY_FORCE, 1);
>>>>
>>>> sb_start_intwrite(sbi->sb);
>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>> index d01c11f5e9c1..f3a5f463496f 100644
>>>> --- a/fs/f2fs/super.c
>>>> +++ b/fs/f2fs/super.c
>>>> @@ -1012,6 +1012,8 @@ static void f2fs_put_super(struct super_block *sb)
>>>> write_checkpoint(sbi, &cpc);
>>>> }
>>>>
>>>> + destroy_gc_context(sbi);
>>>> +
>>>> /* write_checkpoint can update stat informaion */
>>>> f2fs_destroy_stats(sbi);
>>>>
>>>> @@ -1044,6 +1046,7 @@ 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++)
>>>> @@ -1476,11 +1479,11 @@ 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) {
>>>> + if (GC_I(sbi)->f2fs_gc_task) {
>>>> stop_gc_thread(sbi);
>>>> need_restart_gc = true;
>>>> }
>>>> - } else if (!sbi->gc_thread) {
>>>> + } else if (!GC_I(sbi)->f2fs_gc_task) {
>>>> err = start_gc_thread(sbi);
>>>> if (err)
>>>> goto restore_opts;
>>>> @@ -2771,6 +2774,10 @@ 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 +2988,8 @@ 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..fb3cd477d985 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)
>>>> @@ -252,9 +252,9 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
>>>>
>>>> if (!strcmp(a->attr.name, "iostat_enable") && *ui == 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 (!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);
>>>> }
>>>>
>>>> --
>>>> 2.15.0.55.gc2ece9dc4de6
>>>
>>> .
>>>
>
> .
>

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In reply to: Jaegeuk Kim: "Re: [PATCH 5/5] f2fs: fix to avoid race during access gc_thread pointer"
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