Each CPU has SHMEM_INO_BATCH inodes available in `->ino_batch' which is
per-CPU. Access here is serialized by disabling preemption. If the pool is
empty, it gets reloaded from `->next_ino'. Access here is serialized by
->stat_lock which is a spinlock_t and can not be acquired with disabled
preemption.
One way around it would make per-CPU ino_batch struct containing the inode
number a local_lock_t.
Another solution is to promote ->stat_lock to a raw_spinlock_t. The critical
sections are short. The mpol_put() must be moved outside of the critical
section to avoid invoking the destructor with disabled preemption.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
include/linux/shmem_fs.h | 2 +-
mm/shmem.c | 31 +++++++++++++++++--------------
2 files changed, 18 insertions(+), 15 deletions(-)
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 8e775ce517bb3..0a8499fb9c3cb 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -31,7 +31,7 @@ struct shmem_sb_info {
struct percpu_counter used_blocks; /* How many are allocated */
unsigned long max_inodes; /* How many inodes are allowed */
unsigned long free_inodes; /* How many are left for allocation */
- spinlock_t stat_lock; /* Serialize shmem_sb_info changes */
+ raw_spinlock_t stat_lock; /* Serialize shmem_sb_info changes */
umode_t mode; /* Mount mode for root directory */
unsigned char huge; /* Whether to try for hugepages */
kuid_t uid; /* Mount uid for root directory */
diff --git a/mm/shmem.c b/mm/shmem.c
index 70d9ce294bb49..1b95afc4483c1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -278,10 +278,10 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
ino_t ino;
if (!(sb->s_flags & SB_KERNMOUNT)) {
- spin_lock(&sbinfo->stat_lock);
+ raw_spin_lock(&sbinfo->stat_lock);
if (sbinfo->max_inodes) {
if (!sbinfo->free_inodes) {
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
return -ENOSPC;
}
sbinfo->free_inodes--;
@@ -304,7 +304,7 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
}
*inop = ino;
}
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
} else if (inop) {
/*
* __shmem_file_setup, one of our callers, is lock-free: it
@@ -319,13 +319,14 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
* to worry about things like glibc compatibility.
*/
ino_t *next_ino;
+
next_ino = per_cpu_ptr(sbinfo->ino_batch, get_cpu());
ino = *next_ino;
if (unlikely(ino % SHMEM_INO_BATCH == 0)) {
- spin_lock(&sbinfo->stat_lock);
+ raw_spin_lock(&sbinfo->stat_lock);
ino = sbinfo->next_ino;
sbinfo->next_ino += SHMEM_INO_BATCH;
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
if (unlikely(is_zero_ino(ino)))
ino++;
}
@@ -341,9 +342,9 @@ static void shmem_free_inode(struct super_block *sb)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
if (sbinfo->max_inodes) {
- spin_lock(&sbinfo->stat_lock);
+ raw_spin_lock(&sbinfo->stat_lock);
sbinfo->free_inodes++;
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
}
}
@@ -1453,10 +1454,10 @@ static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
struct mempolicy *mpol = NULL;
if (sbinfo->mpol) {
- spin_lock(&sbinfo->stat_lock); /* prevent replace/use races */
+ raw_spin_lock(&sbinfo->stat_lock); /* prevent replace/use races */
mpol = sbinfo->mpol;
mpol_get(mpol);
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
}
return mpol;
}
@@ -3500,9 +3501,10 @@ static int shmem_reconfigure(struct fs_context *fc)
struct shmem_options *ctx = fc->fs_private;
struct shmem_sb_info *sbinfo = SHMEM_SB(fc->root->d_sb);
unsigned long inodes;
+ struct mempolicy *mpol = NULL;
const char *err;
- spin_lock(&sbinfo->stat_lock);
+ raw_spin_lock(&sbinfo->stat_lock);
inodes = sbinfo->max_inodes - sbinfo->free_inodes;
if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
if (!sbinfo->max_blocks) {
@@ -3547,14 +3549,15 @@ static int shmem_reconfigure(struct fs_context *fc)
* Preserve previous mempolicy unless mpol remount option was specified.
*/
if (ctx->mpol) {
- mpol_put(sbinfo->mpol);
+ mpol = sbinfo->mpol;
sbinfo->mpol = ctx->mpol; /* transfers initial ref */
ctx->mpol = NULL;
}
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
+ mpol_put(mpol);
return 0;
out:
- spin_unlock(&sbinfo->stat_lock);
+ raw_spin_unlock(&sbinfo->stat_lock);
return invalfc(fc, "%s", err);
}
@@ -3671,7 +3674,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
sbinfo->mpol = ctx->mpol;
ctx->mpol = NULL;
- spin_lock_init(&sbinfo->stat_lock);
+ 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);
--
2.32.0
