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

From: Jaegeuk Kim
Date: Fri May 04 2018 - 14:59:55 EST

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In reply to: Chao Yu: "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 05/02, Chao Yu wrote:
> On 2018/4/28 10:36, Jaegeuk Kim wrote:
> > On 04/27, 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()
> >
> > No? They should be blocked by remount(2).
>
> How about below cases?
>
> - do_remount

Was there no guard to block any filesystem operations?
If it's true, yeah, we need to cover them.

> - do_remount_sb
> - remount_fs
> - f2fs_remount
> - stop_gc_thread
> - fsync
> - f2fs_sync_file
> - file_write_and_wait_range
> - f2fs_write_data_pages
> - __write_data_page
> - should_update_inplace
> - check_inplace_update_policy
> - need_SSR
> : sbi->gc_thread = NULL;
>
> or
>
> - write_data_page
> - allocate_data_block
> - allocate_segment
> - get_ssr_segment
> - select_gc_type
> : sbi->gc_thread = NULL;
>
> 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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