On 12/6/23, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Dec 06, 2023 at 06:24:29PM +0100, Mateusz Guzik wrote:
>> On 12/6/23, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>> > On Wed, Dec 06, 2023 at 05:42:34PM +0100, Mateusz Guzik wrote:
>> >
>> >> That is to say your patchset is probably an improvement, but this
>> >> benchmark uses kernfs which is a total crapper, with code like this in
>> >> kernfs_iop_permission:
>> >>
>> >> root = kernfs_root(kn);
>> >>
>> >> down_read(&root->kernfs_iattr_rwsem);
>> >> kernfs_refresh_inode(kn, inode);
>> >> ret = generic_permission(&nop_mnt_idmap, inode, mask);
>> >> up_read(&root->kernfs_iattr_rwsem);
>> >>
>> >>
>> >> Maybe there is an easy way to dodge this, off hand I don't see one.
>> >
>> > At a guess - seqcount on kernfs nodes, bumped on metadata changes
>> > and a seqretry loop, not that this was the only problem with kernfs
>> > scalability.
>> >
>>
>> I assumed you can't have possibly changing inode fields around
>> generic_permission.
>
> That's not the problem; kernfs_refresh_inode(), OTOH, is.
> Locking in kernfs is really atrocious ;-/
>
> I would prefer to make that thing per-node (and not an rwsem, obviously,
> seqloct_t would suffice), but let's see what the minimal change would do
> - turn that into a mutex + seqcount and keep them in the same place.
>
So I checked what this strenng test is doing to begin with and I don't
think it is worth spending much time on.
most important bit:
[snip]
57566 newfstatat(AT_FDCWD, "/sys", {st_mode=S_IFDIR|0555, st_size=0,
...}, 0) = 0
57566 ustat(makedev(0, 0x15), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/proc", {st_mode=S_IFDIR|0555, st_size=0,
...}, 0) = 0
57566 ustat(makedev(0, 0x16), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/dev", {st_mode=S_IFDIR|0755,
st_size=3180, ...}, 0) = 0
57566 ustat(makedev(0, 0x5), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/dev/pts", {st_mode=S_IFDIR|0755,
st_size=0, ...}, 0) = 0
57566 ustat(makedev(0, 0x17), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/run", {st_mode=S_IFDIR|0755, st_size=540,
...}, 0) = 0
57566 ustat(makedev(0, 0x18), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/", {st_mode=S_IFDIR|0755, st_size=4096,
...}, 0) = 0
57566 ustat(makedev(0xfe, 0x1), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/sys/kernel/security",
{st_mode=S_IFDIR|0755, st_size=0, ...}, 0) = 0
57566 ustat(makedev(0, 0x6), 0x7ffc47378270) = 0
57566 newfstatat(AT_FDCWD, "/sys/fs/selinux", {st_mode=S_IFDIR|0755,
st_size=0, ...}, 0) = 0
57566 ustat(makedev(0, 0x14), 0x7ffc47378270) = 0
[/snip]
This is part of a loop which also does a bunch of statfs of similar sort.
Bottom line though is that it keeps microbenchmarking *all* mounted
filesystems, most of which are never subjected to this kind of work in
the real world.
I got lock stat from your work.dcache2 branch before you sent the
patch. It had kernfs on it, but it was not standing out compared to
other filesystems. Rerunning this now (again without the patch you
just sent) only gives read locks, I don't know why. Anyhow majority of
lock_stat output is pasted at the end.
Top of the profile is dentry->d_lock in common codepaths, presumably
one does not need stressng to run into that.
After that sb_lock in user_get_super and drop_super. I think it is
unsound that lookup by dev number callable by userspace is done in
O(n), I would suggest a RB tree keyed on dev here. Regardless of that
refcount could be changed with atomics and dropped with
atomic_dec_unless (or whatever the name), then drop_super would avoid
taking the lock in the common case. I can hack it up if it sounds
reasonable.
The rest is contention within filesystems which did not expect to be
running into it and which imo is not worth poking at.
That is to say the real regression to investigate imo is that
unixbench drop by 11%. I did not find instructions how to reproduce
it, but sent an e-mail asking about it. Will look into it after I get
a response.
lock_stat version 0.4
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
class name con-bounces contentions
waittime-min waittime-max waittime-total waittime-avg
acq-bounces acquisitions holdtime-min holdtime-max
holdtime-total holdtime-avg
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
&dentry->d_lock: 24924207 24987328
0.05 2306.93 9523158.78 0.38
225395365 405715020 0.04 2179.42 50129873.85
0.12
---------------
&dentry->d_lock 12359237
[<00000000dd9f6f18>] dput+0xf0/0x240
&dentry->d_lock 10061783
[<00000000834ba9a3>] lockref_get_not_dead+0xc/0x30
&dentry->d_lock 1233395
[<000000004eae9c7d>] __d_lookup+0x80/0x100
&dentry->d_lock 1147006
[<00000000d3f25dc0>] lockref_get+0x9/0x20
---------------
&dentry->d_lock 1232931
[<00000000d3f25dc0>] lockref_get+0x9/0x20
&dentry->d_lock 11326396
[<00000000dd9f6f18>] dput+0xf0/0x240
&dentry->d_lock 10462141
[<00000000834ba9a3>] lockref_get_not_dead+0xc/0x30
&dentry->d_lock 1512612
[<000000004eae9c7d>] __d_lookup+0x80/0x100
.............................................................................................................................................................................................................................
sb_lock: 3751297 3785255
0.06 333.93 2084502.27 0.55
14120549 29289318 0.04 483.38 6902926.62
0.24
-------
sb_lock 1679258
[<00000000cebb0a72>] user_get_super+0x1a/0xc0
sb_lock 2105997
[<00000000794955d0>] drop_super+0x1e/0x40
-------
sb_lock 2990448
[<00000000cebb0a72>] user_get_super+0x1a/0xc0
sb_lock 794807
[<00000000794955d0>] drop_super+0x1e/0x40
.............................................................................................................................................................................................................................
sysctl_lock: 798762 959533
0.06 564.08 428809.34 0.45
5390215 21301415 0.04 704.25 1883405.47
0.09
-----------
sysctl_lock 504903
[<000000003894310e>] proc_sys_permission+0x88/0xe0
sysctl_lock 288674
[<00000000824e71e4>] proc_sys_permission+0x43/0xe0
sysctl_lock 165956
[<0000000097dd1ac9>] proc_sys_compare+0x5a/0xc0
-----------
sysctl_lock 612689
[<00000000824e71e4>] proc_sys_permission+0x43/0xe0
sysctl_lock 229185
[<000000003894310e>] proc_sys_permission+0x88/0xe0
sysctl_lock 117659
[<0000000097dd1ac9>] proc_sys_compare+0x5a/0xc0
.............................................................................................................................................................................................................................
key#9: 129050 129076
0.06 24.89 46463.88 0.36
8406664 10650710 0.17 243.33 3314905.24
0.31
-----
key#9 129076
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
-----
key#9 129076
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
.............................................................................................................................................................................................................................
&sbi->fs_lock: 84490 84572
0.07 105.87 30626.76 0.36
3679250 4260272 0.22 262.79 1380049.79
0.32
-------------
&sbi->fs_lock 84572
[<00000000892170e2>] autofs_d_manage+0x131/0x180 [autofs4]
-------------
&sbi->fs_lock 84572
[<00000000892170e2>] autofs_d_manage+0x131/0x180 [autofs4]
.............................................................................................................................................................................................................................
&sbi->fs_lock: 84490 84572
0.07 105.87 30626.76 0.36
3679250 4260272 0.22 262.79 1380049.79
0.32
-------------
&sbi->fs_lock 84572
[<00000000892170e2>] autofs_d_manage+0x131/0x180 [autofs4]
-------------
&sbi->fs_lock 84572
[<00000000892170e2>] autofs_d_manage+0x131/0x180 [autofs4]
.............................................................................................................................................................................................................................
key#1: 20226 20253
0.13 6.05 11867.42 0.59
290374 444723 0.04 8.89 54524.68
0.12
key#1: 13800 13807
0.06 17.65 3355.74 0.24
1706485 2133314 0.13 41.81 582531.55
0.27
-----
key#1 13807
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
-----
key#1 13807
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
.............................................................................................................................................................................................................................
key#1: 10807 10810
0.06 29.43 2734.23 0.25
1706470 2130177 0.16 60.15 509922.56
0.24
-----
key#1 10810
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
-----
key#1 10810
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
.............................................................................................................................................................................................................................
key#1: 10070 10072
0.05 12.74 2451.46 0.24
1706475 2130411 0.13 18.58 600087.26
0.28
-----
key#1 10072
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
-----
key#1 10072
[<000000003d1d6559>] __percpu_counter_sum+0xc/0x70
.............................................................................................................................................................................................................................
&sb->s_type->i_mutex_key#1: 9330 9357
0.08 674.82 10029.38 1.07
565340 1065074 0.17 468.85 546956.77
0.51
--------------------------
&sb->s_type->i_mutex_key#1 4052
[<0000000054b2779b>] configfs_dir_close+0x25/0xb0 [configfs]
&sb->s_type->i_mutex_key#1 5305
[<00000000277d0929>] configfs_dir_open+0x2e/0xa0 [configfs]
--------------------------
&sb->s_type->i_mutex_key#1 8218
[<00000000277d0929>] configfs_dir_open+0x2e/0xa0 [configfs]
&sb->s_type->i_mutex_key#1 1139
[<0000000054b2779b>] configfs_dir_close+0x25/0xb0 [configfs]
.............................................................................................................................................................................................................................
&sbinfo->stat_lock#2: 9099 9105
0.06 73.97 2843.24 0.31
1694004 2130138 0.04 79.57 172592.98
0.08
--------------------
&sbinfo->stat_lock#2 9105
[<0000000063446d75>] hugetlbfs_statfs+0x7f/0xf0
--------------------
&sbinfo->stat_lock#2 9105
[<0000000063446d75>] hugetlbfs_statfs+0x7f/0xf0
> Below is completely untested, just to see if it would affect the sysinfo
> side of things (both with and without dcache series - it's independent
> from that):
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 8b2bd65d70e7..2784ac117a1f 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -383,11 +383,13 @@ static int kernfs_link_sibling(struct kernfs_node
> *kn)
> rb_insert_color(&kn->rb, &kn->parent->dir.children);
>
> /* successfully added, account subdir number */
> - down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + mutex_lock(&kernfs_root(kn)->kernfs_iattr_lock);
> + write_seqcount_begin(&kernfs_root(kn)->kernfs_iattr_seq);
> if (kernfs_type(kn) == KERNFS_DIR)
> kn->parent->dir.subdirs++;
> kernfs_inc_rev(kn->parent);
> - up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + write_seqcount_end(&kernfs_root(kn)->kernfs_iattr_seq);
> + mutex_unlock(&kernfs_root(kn)->kernfs_iattr_lock);
>
> return 0;
> }
> @@ -410,11 +412,12 @@ static bool kernfs_unlink_sibling(struct kernfs_node
> *kn)
> if (RB_EMPTY_NODE(&kn->rb))
> return false;
>
> - down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + mutex_lock(&kernfs_root(kn)->kernfs_iattr_lock);
> + write_seqcount_begin(&kernfs_root(kn)->kernfs_iattr_seq);
> if (kernfs_type(kn) == KERNFS_DIR)
> kn->parent->dir.subdirs--;
> - kernfs_inc_rev(kn->parent);
> - up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + write_seqcount_end(&kernfs_root(kn)->kernfs_iattr_seq);
> + mutex_unlock(&kernfs_root(kn)->kernfs_iattr_lock);
>
> rb_erase(&kn->rb, &kn->parent->dir.children);
> RB_CLEAR_NODE(&kn->rb);
> @@ -639,15 +642,11 @@ static struct kernfs_node *__kernfs_new_node(struct
> kernfs_root *root,
> kn->flags = flags;
>
> if (!uid_eq(uid, GLOBAL_ROOT_UID) || !gid_eq(gid, GLOBAL_ROOT_GID)) {
> - struct iattr iattr = {
> - .ia_valid = ATTR_UID | ATTR_GID,
> - .ia_uid = uid,
> - .ia_gid = gid,
> - };
> -
> - ret = __kernfs_setattr(kn, &iattr);
> - if (ret < 0)
> + kn->iattr = kernfs_alloc_iattrs(uid, gid);
> + if (!kn->iattr) {
> + ret = -ENOMEM;
> goto err_out3;
> + }
> }
>
> if (parent) {
> @@ -776,7 +775,8 @@ int kernfs_add_one(struct kernfs_node *kn)
> goto out_unlock;
>
> /* Update timestamps on the parent */
> - down_write(&root->kernfs_iattr_rwsem);
> + mutex_lock(&root->kernfs_iattr_lock);
> + write_seqcount_begin(&root->kernfs_iattr_seq);
>
> ps_iattr = parent->iattr;
> if (ps_iattr) {
> @@ -784,7 +784,8 @@ int kernfs_add_one(struct kernfs_node *kn)
> ps_iattr->ia_mtime = ps_iattr->ia_ctime;
> }
>
> - up_write(&root->kernfs_iattr_rwsem);
> + write_seqcount_end(&root->kernfs_iattr_seq);
> + mutex_unlock(&root->kernfs_iattr_lock);
> up_write(&root->kernfs_rwsem);
>
> /*
> @@ -949,7 +950,8 @@ struct kernfs_root *kernfs_create_root(struct
> kernfs_syscall_ops *scops,
>
> idr_init(&root->ino_idr);
> init_rwsem(&root->kernfs_rwsem);
> - init_rwsem(&root->kernfs_iattr_rwsem);
> + mutex_init(&root->kernfs_iattr_lock);
> + seqcount_mutex_init(&root->kernfs_iattr_seq, &root->kernfs_iattr_lock);
> init_rwsem(&root->kernfs_supers_rwsem);
> INIT_LIST_HEAD(&root->supers);
>
> @@ -1473,14 +1475,16 @@ static void __kernfs_remove(struct kernfs_node *kn)
> pos->parent ? pos->parent->iattr : NULL;
>
> /* update timestamps on the parent */
> - down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + mutex_lock(&kernfs_root(kn)->kernfs_iattr_lock);
> + write_seqcount_begin(&kernfs_root(kn)->kernfs_iattr_seq);
>
> if (ps_iattr) {
> ktime_get_real_ts64(&ps_iattr->ia_ctime);
> ps_iattr->ia_mtime = ps_iattr->ia_ctime;
> }
>
> - up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
> + write_seqcount_end(&kernfs_root(kn)->kernfs_iattr_seq);
> + mutex_unlock(&kernfs_root(kn)->kernfs_iattr_lock);
> kernfs_put(pos);
> }
>
> diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
> index b83054da68b3..4b77931c814d 100644
> --- a/fs/kernfs/inode.c
> +++ b/fs/kernfs/inode.c
> @@ -24,56 +24,49 @@ static const struct inode_operations kernfs_iops = {
> .listxattr = kernfs_iop_listxattr,
> };
>
> -static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, int
> alloc)
> +struct kernfs_iattrs *kernfs_alloc_iattrs(kuid_t uid, kgid_t gid)
> {
> - static DEFINE_MUTEX(iattr_mutex);
> - struct kernfs_iattrs *ret;
> + struct kernfs_iattrs *ret = kmem_cache_zalloc(kernfs_iattrs_cache,
> GFP_KERNEL);
>
> - mutex_lock(&iattr_mutex);
> + if (ret) {
> + ret->ia_uid = uid;
> + ret->ia_gid = gid;
>
> - if (kn->iattr || !alloc)
> - goto out_unlock;
> + ktime_get_real_ts64(&ret->ia_atime);
> + ret->ia_ctime = ret->ia_mtime = ret->ia_atime;
>
> - kn->iattr = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
> - if (!kn->iattr)
> - goto out_unlock;
> -
> - /* assign default attributes */
> - kn->iattr->ia_uid = GLOBAL_ROOT_UID;
> - kn->iattr->ia_gid = GLOBAL_ROOT_GID;
> -
> - ktime_get_real_ts64(&kn->iattr->ia_atime);
> - kn->iattr->ia_mtime = kn->iattr->ia_atime;
> - kn->iattr->ia_ctime = kn->iattr->ia_atime;
> -
> - simple_xattrs_init(&kn->iattr->xattrs);
> - atomic_set(&kn->iattr->nr_user_xattrs, 0);
> - atomic_set(&kn->iattr->user_xattr_size, 0);
> -out_unlock:
> - ret = kn->iattr;
> - mutex_unlock(&iattr_mutex);
> + simple_xattrs_init(&ret->xattrs);
> + atomic_set(&ret->nr_user_xattrs, 0);
> + atomic_set(&ret->user_xattr_size, 0);
> + }
> return ret;
> }
>
> static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
> {
> - return __kernfs_iattrs(kn, 1);
> + struct kernfs_iattrs *ret = READ_ONCE(kn->iattr);
> +
> + if (!ret) {
> + struct kernfs_iattrs *new;
> + new = kernfs_alloc_iattrs(GLOBAL_ROOT_UID, GLOBAL_ROOT_GID);
> + ret = cmpxchg(&kn->iattr, NULL, new);
> + if (likely(!ret))
> + return new;
> + kfree(new);
> + }
> + return ret;
> }
>
> static struct kernfs_iattrs *kernfs_iattrs_noalloc(struct kernfs_node *kn)
> {
> - return __kernfs_iattrs(kn, 0);
> + return READ_ONCE(kn->iattr);
> }
>
> -int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
> +static void __kernfs_setattr(struct kernfs_node *kn, const struct iattr
> *iattr)
> {
> - struct kernfs_iattrs *attrs;
> + struct kernfs_iattrs *attrs = kernfs_iattrs_noalloc(kn);
> unsigned int ia_valid = iattr->ia_valid;
>
> - attrs = kernfs_iattrs(kn);
> - if (!attrs)
> - return -ENOMEM;
> -
> if (ia_valid & ATTR_UID)
> attrs->ia_uid = iattr->ia_uid;
> if (ia_valid & ATTR_GID)
> @@ -86,7 +79,6 @@ int __kernfs_setattr(struct kernfs_node *kn, const struct
> iattr *iattr)
> attrs->ia_ctime = iattr->ia_ctime;
> if (ia_valid & ATTR_MODE)
> kn->mode = iattr->ia_mode;
> - return 0;
> }
>
> /**
> @@ -98,13 +90,17 @@ int __kernfs_setattr(struct kernfs_node *kn, const
> struct iattr *iattr)
> */
> int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
> {
> - int ret;
> struct kernfs_root *root = kernfs_root(kn);
>
> - down_write(&root->kernfs_iattr_rwsem);
> - ret = __kernfs_setattr(kn, iattr);
> - up_write(&root->kernfs_iattr_rwsem);
> - return ret;
> + if (!kernfs_iattrs(kn))
> + return -ENOMEM;
> +
> + mutex_lock(&root->kernfs_iattr_lock);
> + write_seqcount_begin(&root->kernfs_iattr_seq);
> + __kernfs_setattr(kn, iattr);
> + write_seqcount_end(&root->kernfs_iattr_seq);
> + mutex_unlock(&root->kernfs_iattr_lock);
> + return 0;
> }
>
> int kernfs_iop_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> @@ -117,22 +113,23 @@ int kernfs_iop_setattr(struct mnt_idmap *idmap, struct
> dentry *dentry,
>
> if (!kn)
> return -EINVAL;
> + if (!kernfs_iattrs(kn))
> + return -ENOMEM;
>
> root = kernfs_root(kn);
> - down_write(&root->kernfs_iattr_rwsem);
> + mutex_lock(&root->kernfs_iattr_lock);
> + write_seqcount_begin(&root->kernfs_iattr_seq);
> error = setattr_prepare(&nop_mnt_idmap, dentry, iattr);
> if (error)
> goto out;
>
> - error = __kernfs_setattr(kn, iattr);
> - if (error)
> - goto out;
> -
> + __kernfs_setattr(kn, iattr);
> /* this ignores size changes */
> setattr_copy(&nop_mnt_idmap, inode, iattr);
>
> out:
> - up_write(&root->kernfs_iattr_rwsem);
> + write_seqcount_end(&root->kernfs_iattr_seq);
> + mutex_unlock(&root->kernfs_iattr_lock);
> return error;
> }
>
> @@ -187,11 +184,13 @@ int kernfs_iop_getattr(struct mnt_idmap *idmap,
> struct inode *inode = d_inode(path->dentry);
> struct kernfs_node *kn = inode->i_private;
> struct kernfs_root *root = kernfs_root(kn);
> + unsigned seq;
>
> - down_read(&root->kernfs_iattr_rwsem);
> - kernfs_refresh_inode(kn, inode);
> - generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
> - up_read(&root->kernfs_iattr_rwsem);
> + do {
> + seq = read_seqcount_begin(&root->kernfs_iattr_seq);
> + kernfs_refresh_inode(kn, inode);
> + generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
> + } while (read_seqcount_retry(&root->kernfs_iattr_seq, seq));
>
> return 0;
> }
> @@ -276,7 +275,7 @@ int kernfs_iop_permission(struct mnt_idmap *idmap,
> {
> struct kernfs_node *kn;
> struct kernfs_root *root;
> - int ret;
> + unsigned seq;
>
> if (mask & MAY_NOT_BLOCK)
> return -ECHILD;
> @@ -284,12 +283,11 @@ int kernfs_iop_permission(struct mnt_idmap *idmap,
> kn = inode->i_private;
> root = kernfs_root(kn);
>
> - down_read(&root->kernfs_iattr_rwsem);
> - kernfs_refresh_inode(kn, inode);
> - ret = generic_permission(&nop_mnt_idmap, inode, mask);
> - up_read(&root->kernfs_iattr_rwsem);
> -
> - return ret;
> + do {
> + seq = read_seqcount_begin(&root->kernfs_iattr_seq);
> + kernfs_refresh_inode(kn, inode);
> + } while (read_seqcount_retry(&root->kernfs_iattr_seq, seq));
> + return generic_permission(&nop_mnt_idmap, inode, mask);
> }
>
> int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
> diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
> index 237f2764b941..0aea5151ed1a 100644
> --- a/fs/kernfs/kernfs-internal.h
> +++ b/fs/kernfs/kernfs-internal.h
> @@ -47,7 +47,8 @@ struct kernfs_root {
>
> wait_queue_head_t deactivate_waitq;
> struct rw_semaphore kernfs_rwsem;
> - struct rw_semaphore kernfs_iattr_rwsem;
> + struct mutex kernfs_iattr_lock;
> + seqcount_mutex_t kernfs_iattr_seq;
> struct rw_semaphore kernfs_supers_rwsem;
> };
>
> @@ -137,7 +138,7 @@ int kernfs_iop_getattr(struct mnt_idmap *idmap,
> const struct path *path, struct kstat *stat,
> u32 request_mask, unsigned int query_flags);
> ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t
> size);
> -int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
> +struct kernfs_iattrs *kernfs_alloc_iattrs(kuid_t uid, kgid_t gid);
>
> /*
> * dir.c
>
--
Mateusz Guzik <mjguzik gmail.com>
