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shmem: use raw_spinlock_t for ->stat_lock 

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.

Link: https://lkml.kernel.org/r/20210806142916.jdwkb5bx62q5fwfo@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sebastian Andrzej Siewior 2021-09-02 14:54:03 -07:00 committed by Linus Torvalds
parent 3969b1a654
commit bf11b9a8e9
2 changed files with 18 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/shmem_fs.h
View File

@ -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 */

31
mm/shmem.c
View File

@ -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;
}
@ -3488,9 +3489,10 @@ 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) {
@ -3535,14 +3537,15 @@ 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);
}
@ -3659,7 +3662,7 @@ 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);