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Subject[PATCH v1] shmem: change shrinklist_lock form spinlock to mutex and move iput into it
Date
This patch fixes commit 779750d20b93 ("shmem: split huge pages
beyond i_size under memory pressure").

iput out of sbinfo->shrinklist_lock will let shmem_evict_inode grab
and delete the inode, which will berak the consistency between
shrinklist_len and shrinklist. The simultaneous deletion of adjacent
elements in the local list "list" by shmem_unused_huge_shrink and
shmem_evict_inode will also break the list.

iput must in lock or after lock, but shrinklist_lock is a spinlock
which can not sleep and iput may sleep.[1]

Fix it by changing shrinklist_lock from spinlock to mutex and moving iput
into this lock.

[1]. Link: http://lkml.kernel.org/r/20170131093141.GA15899@node.shutemov.name
Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure")
Signed-off-by: Gang Li <ligang.bdlg@bytedance.com>
---
include/linux/shmem_fs.h | 2 +-
mm/shmem.c | 16 +++++++---------
2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 166158b6e917..65804fd264d0 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -41,7 +41,7 @@ struct shmem_sb_info {
ino_t next_ino; /* The next per-sb inode number to use */
ino_t __percpu *ino_batch; /* The next per-cpu inode number to use */
struct mempolicy *mpol; /* default memory policy for mappings */
- spinlock_t shrinklist_lock; /* Protects shrinklist */
+ struct mutex shrinklist_mutex;/* Protects shrinklist */
struct list_head shrinklist; /* List of shinkable inodes */
unsigned long shrinklist_len; /* Length of shrinklist */
};
diff --git a/mm/shmem.c b/mm/shmem.c
index 18f93c2d68f1..2165a28631c5 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -559,7 +559,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
if (list_empty(&sbinfo->shrinklist))
return SHRINK_STOP;

- spin_lock(&sbinfo->shrinklist_lock);
+ mutex_lock(&sbinfo->shrinklist_mutex);
list_for_each_safe(pos, next, &sbinfo->shrinklist) {
info = list_entry(pos, struct shmem_inode_info, shrinklist);

@@ -586,7 +586,6 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
if (!--batch)
break;
}
- spin_unlock(&sbinfo->shrinklist_lock);

list_for_each_safe(pos, next, &to_remove) {
info = list_entry(pos, struct shmem_inode_info, shrinklist);
@@ -643,10 +642,9 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
iput(inode);
}

- spin_lock(&sbinfo->shrinklist_lock);
list_splice_tail(&list, &sbinfo->shrinklist);
sbinfo->shrinklist_len -= removed;
- spin_unlock(&sbinfo->shrinklist_lock);
+ mutex_unlock(&sbinfo->shrinklist_mutex);

return split;
}
@@ -1137,12 +1135,12 @@ static void shmem_evict_inode(struct inode *inode)
inode->i_size = 0;
shmem_truncate_range(inode, 0, (loff_t)-1);
if (!list_empty(&info->shrinklist)) {
- spin_lock(&sbinfo->shrinklist_lock);
+ mutex_lock(&sbinfo->shrinklist_mutex);
if (!list_empty(&info->shrinklist)) {
list_del_init(&info->shrinklist);
sbinfo->shrinklist_len--;
}
- spin_unlock(&sbinfo->shrinklist_lock);
+ mutex_unlock(&sbinfo->shrinklist_mutex);
}
while (!list_empty(&info->swaplist)) {
/* Wait while shmem_unuse() is scanning this inode... */
@@ -1954,7 +1952,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
* Part of the huge page is beyond i_size: subject
* to shrink under memory pressure.
*/
- spin_lock(&sbinfo->shrinklist_lock);
+ mutex_lock(&sbinfo->shrinklist_mutex);
/*
* _careful to defend against unlocked access to
* ->shrink_list in shmem_unused_huge_shrink()
@@ -1964,7 +1962,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
&sbinfo->shrinklist);
sbinfo->shrinklist_len++;
}
- spin_unlock(&sbinfo->shrinklist_lock);
+ mutex_unlock(&sbinfo->shrinklist_mutex);
}

/*
@@ -3652,7 +3650,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
raw_spin_lock_init(&sbinfo->stat_lock);
if (percpu_counter_init(&sbinfo->used_blocks, 0, GFP_KERNEL))
goto failed;
- spin_lock_init(&sbinfo->shrinklist_lock);
+ mutex_init(&sbinfo->shrinklist_mutex);
INIT_LIST_HEAD(&sbinfo->shrinklist);

sb->s_maxbytes = MAX_LFS_FILESIZE;
--
2.20.1
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