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Message-ID: <20180507122659.86536-1-yuchao0@huawei.com>
Date: Mon, 7 May 2018 20:26:59 +0800
From: Chao Yu <yuchao0@...wei.com>
To: <jaegeuk@...nel.org>
CC: <linux-f2fs-devel@...ts.sourceforge.net>,
<linux-kernel@...r.kernel.org>, <chao@...nel.org>,
Chao Yu <yuchao0@...wei.com>
Subject: [PATCH v4] f2fs: fix to avoid race during access gc_thread pointer
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.
fs/f2fs/f2fs.h | 1 +
fs/f2fs/gc.c | 4 ++++
fs/f2fs/segment.c | 11 ++++++++++-
fs/f2fs/super.c | 19 ++++++++++++++-----
fs/f2fs/sysfs.c | 14 +++++++++++---
5 files changed, 40 insertions(+), 9 deletions(-)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 80490a7991a7..e238d0ea0be7 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1191,6 +1191,7 @@ struct f2fs_sb_info {
/* for cleaning operations */
struct mutex gc_mutex; /* mutex for GC */
+ struct rw_semaphore gc_rwsem; /* rw semaphore for gc_thread */
struct f2fs_gc_kthread *gc_thread; /* GC thread */
unsigned int cur_victim_sec; /* current victim section num */
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 9bb2ddbbed1e..b74714be7be7 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -187,17 +187,21 @@ 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 {
+ down_read(&sbi->gc_rwsem);
p->gc_mode = select_gc_type(sbi->gc_thread, gc_type);
+ up_read(&sbi->gc_rwsem);
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 */
+ down_read(&sbi->gc_rwsem);
if (gc_type != FG_GC &&
(sbi->gc_thread && !sbi->gc_thread->gc_urgent) &&
p->max_search > sbi->max_victim_search)
p->max_search = sbi->max_victim_search;
+ up_read(&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/segment.c b/fs/f2fs/segment.c
index 320cc1c57246..33d146939048 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -174,11 +174,18 @@ bool need_SSR(struct f2fs_sb_info *sbi)
int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
+ bool gc_urgent = false;
if (test_opt(sbi, LFS))
return false;
+
+ down_read(&sbi->gc_rwsem);
if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
- return true;
+ gc_urgent = true;
+ up_read(&sbi->gc_rwsem);
+
+ if (gc_urgent)
+ return false;
return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
@@ -1421,8 +1428,10 @@ static int issue_discard_thread(void *data)
if (dcc->discard_wake)
dcc->discard_wake = 0;
+ down_read(&sbi->gc_rwsem);
if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
init_discard_policy(&dpolicy, DPOLICY_FORCE, 1);
+ up_read(&sbi->gc_rwsem);
sb_start_intwrite(sbi->sb);
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index c8e5fe5d71fe..294be9e92aee 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1476,15 +1476,23 @@ 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)) {
+ down_write(&sbi->gc_rwsem);
if (sbi->gc_thread) {
stop_gc_thread(sbi);
need_restart_gc = true;
}
- } else if (!sbi->gc_thread) {
- err = start_gc_thread(sbi);
- if (err)
- goto restore_opts;
- need_stop_gc = true;
+ up_write(&sbi->gc_rwsem);
+ } else {
+ down_write(&sbi->gc_rwsem);
+ if (!sbi->gc_thread) {
+ err = start_gc_thread(sbi);
+ if (err) {
+ up_write(&sbi->gc_rwsem);
+ goto restore_opts;
+ }
+ need_stop_gc = true;
+ }
+ up_write(&sbi->gc_rwsem);
}
if (*flags & SB_RDONLY ||
@@ -2802,6 +2810,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
}
init_rwsem(&sbi->cp_rwsem);
+ init_rwsem(&sbi->gc_rwsem);
init_waitqueue_head(&sbi->cp_wait);
init_sb_info(sbi);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 6d8d8f41e517..34c542dbc459 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -173,6 +173,7 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
unsigned long t;
unsigned int *ui;
ssize_t ret;
+ bool gc_entry = (a->struct_type == GC_THREAD);
ptr = __struct_ptr(sbi, a->struct_type);
if (!ptr)
@@ -248,16 +249,23 @@ 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 (gc_entry)
+ down_read(&sbi->gc_rwsem);
+
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);
}
+ *ui = t;
+
+ if (gc_entry)
+ up_read(&sbi->gc_rwsem);
+
return count;
}
--
2.17.0.391.g1f1cddd558b5
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