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Message-ID: <20180508031748.GB17507@jaegeuk-macbookpro.roam.corp.google.com>
Date: Mon, 7 May 2018 20:17:48 -0700
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 v4] f2fs: fix to avoid race during access gc_thread
pointer
On 05/08, Chao Yu wrote:
> On 2018/5/8 5:36, Jaegeuk Kim wrote:
> > On 05/07, 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.
> >>
> >> In order to fix this issue, introduce gc_rwsem to exclude those operations.
> >>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >> v4:
> >> - use introduced sbi.gc_rwsem lock instead of sb.s_umount.
> >
> > We can use this first.
> >
> >>From e62e8d3ece6ee8a4aeac8ffd6161d25851f8b3f0 Mon Sep 17 00:00:00 2001
> > From: Jaegeuk Kim <jaegeuk@...nel.org>
> > Date: Mon, 7 May 2018 14:22:40 -0700
> > Subject: [PATCH] f2fs: introduce sbi->gc_mode to determine the policy
> >
> > This is to avoid sbi->gc_thread pointer access.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > fs/f2fs/f2fs.h | 8 ++++++++
> > fs/f2fs/gc.c | 28 ++++++++++++----------------
> > fs/f2fs/gc.h | 2 --
> > fs/f2fs/segment.c | 4 ++--
> > fs/f2fs/sysfs.c | 33 +++++++++++++++++++++++++--------
> > 5 files changed, 47 insertions(+), 28 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 80490a7991a7..779d8b26878c 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1065,6 +1065,13 @@ enum {
> > MAX_TIME,
> > };
> >
> > +enum {
> > + GC_NORMAL,
> > + GC_IDLE_CB,
> > + GC_IDLE_GREEDY,
> > + GC_URGENT,
> > +};
> > +
> > enum {
> > WHINT_MODE_OFF, /* not pass down write hints */
> > WHINT_MODE_USER, /* try to pass down hints given by users */
> > @@ -1193,6 +1200,7 @@ struct f2fs_sb_info {
> > struct mutex gc_mutex; /* mutex for GC */
> > struct f2fs_gc_kthread *gc_thread; /* GC thread */
> > unsigned int cur_victim_sec; /* current victim section num */
> > + unsigned int gc_mode; /* current GC state */
> >
> > /* threshold for gc trials on pinned files */
> > u64 gc_pin_file_threshold;
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 9bb2ddbbed1e..7ec8ea75dfde 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -76,7 +76,7 @@ static int gc_thread_func(void *data)
> > * invalidated soon after by user update or deletion.
> > * So, I'd like to wait some time to collect dirty segments.
> > */
> > - if (gc_th->gc_urgent) {
> > + if (sbi->gc_mode == GC_URGENT) {
> > wait_ms = gc_th->urgent_sleep_time;
> > mutex_lock(&sbi->gc_mutex);
> > goto do_gc;
> > @@ -131,8 +131,6 @@ int start_gc_thread(struct f2fs_sb_info *sbi)
> > gc_th->max_sleep_time = DEF_GC_THREAD_MAX_SLEEP_TIME;
> > gc_th->no_gc_sleep_time = DEF_GC_THREAD_NOGC_SLEEP_TIME;
> >
> > - gc_th->gc_idle = 0;
> > - gc_th->gc_urgent = 0;
> > gc_th->gc_wake= 0;
> >
> > sbi->gc_thread = gc_th;
> > @@ -158,21 +156,19 @@ void stop_gc_thread(struct f2fs_sb_info *sbi)
> > sbi->gc_thread = NULL;
> > }
> >
> > -static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
> > +static int select_gc_type(struct f2fs_sb_info *sbi, int gc_type)
> > {
> > int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;
> >
> > - if (!gc_th)
> > - return gc_mode;
> > -
> > - if (gc_th->gc_idle) {
> > - if (gc_th->gc_idle == 1)
> > - gc_mode = GC_CB;
> > - else if (gc_th->gc_idle == 2)
> > - gc_mode = GC_GREEDY;
> > - }
> > - if (gc_th->gc_urgent)
> > + switch (sbi->gc_mode) {
> > + case GC_IDLE_CB:
> > + gc_mode = GC_CB;
> > + break;
> > + case GC_IDLE_GREEDY:
> > + case GC_URGENT:
> > gc_mode = GC_GREEDY;
> > + break;
> > + }
> > return gc_mode;
> > }
> >
> > @@ -187,7 +183,7 @@ 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(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;
> > @@ -195,7 +191,7 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
> >
> > /* 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) &&
> > + (sbi->gc_mode != GC_URGENT) &&
> > p->max_search > sbi->max_victim_search)
> > p->max_search = sbi->max_victim_search;
> >
> > diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
> > index b0045d4c8d1e..c8619e408009 100644
> > --- a/fs/f2fs/gc.h
> > +++ b/fs/f2fs/gc.h
> > @@ -36,8 +36,6 @@ struct f2fs_gc_kthread {
> > unsigned int no_gc_sleep_time;
> >
> > /* for changing gc mode */
> > - unsigned int gc_idle;
> > - unsigned int gc_urgent;
> > unsigned int gc_wake;
> > };
> >
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 503a98abdb2f..5a7ed06291e0 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 (sbi->gc_mode == GC_URGENT)
> > return true;
> >
> > return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
> > @@ -1418,7 +1418,7 @@ 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 (sbi->gc_mode == GC_URGENT)
> > init_discard_policy(&dpolicy, DPOLICY_FORCE, 1);
> >
> > sb_start_intwrite(sbi->sb);
> > diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> > index 6d8d8f41e517..dd940d156af6 100644
> > --- a/fs/f2fs/sysfs.c
> > +++ b/fs/f2fs/sysfs.c
> > @@ -248,16 +248,33 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
> > if (!strcmp(a->attr.name, "trim_sections"))
> > return -EINVAL;
> >
> > + if (!strcmp(a->attr.name, "gc_urgent")) {
> > + if (t >= 1) {
> > + sbi->gc_mode = GC_URGENT;
> > + if (sbi->gc_thread) {
> > + wake_up_interruptible_all(
> > + &sbi->gc_thread->gc_wait_queue_head);
> > + wake_up_discard_thread(sbi, true);
> > + }
> > + } else {
> > + sbi->gc_mode = GC_NORMAL;
> > + }
> > + return count;
> > + }
> > + if (!strcmp(a->attr.name, "gc_idle")) {
> > + if (t == GC_IDLE_CB)
> > + sbi->gc_mode = GC_IDLE_CB;
> > + else if (t == GC_IDLE_GREEDY)
> > + sbi->gc_mode = GC_IDLE_GREEDY;
> > + else
> > + sbi->gc_mode = GC_NORMAL;
> > + return count;
> > + }
> > +
> > *ui = t;
> >
> > 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);
> > - wake_up_discard_thread(sbi, true);
> > - }
> > -
> > return count;
> > }
> >
> > @@ -349,8 +366,8 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_urgent_sleep_time,
> > F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_min_sleep_time, min_sleep_time);
> > F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_max_sleep_time, max_sleep_time);
> > F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_no_gc_sleep_time, no_gc_sleep_time);
>
> All above parameters will be accessed via '*ui = t;', in order to avoid that, we
> need to move all gc_* configuration fields into sbi, so leaving f2fs_gc_kthread
> all most empty.
What I said was to use down_read(&sbi->sb->s_umount); in sysfs.c on top of this.
> IMO, just merge my v1 patch is OK? since that patch makes better
> encapsulation, so that background GC related parameter can still locate in
> independent f2fs_gc_kthread structure rather in common f2fs_sb_info structure.
>
> Thanks,
>
> > -F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
> > -F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_urgent, gc_urgent);
> > +F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_idle, gc_mode);
> > +F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_urgent, gc_mode);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, reclaim_segments, rec_prefree_segments);
> > F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, max_small_discards, max_discards);
> > F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, discard_granularity, discard_granularity);
> >
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