在 2013年2月16日星期六UTC+8上午4时49分15秒，Nathan Zimmer写道：
> I am currently tracking a hotlock reported by a customer on a large system,
>
> 512 cores. I am currently running 3.8-rc7 but the issue looks like it has
> been
>
> this way for a very long time.
>
> The offending lock is proc_dir_entry->pde_unload_lock.
>
>
>
> This patch converts the replaces the lock with the rcu. However the
> pde_openers
>
> list still is controlled by a spin lock. I tested on a 4096 machine and the
> lock
>
> doesn't seem hot at least according to perf.
>
>
>
> This is a refresh/resend of what was orignally suggested by Eric Dumazet some
>
> time ago.
>
>
>
> Supporting numbers, lower is better, they are from the test I posted earlier.
>
> cpuinfo baseline Rcu
>
> tasks read-sec read-sec
>
> 1 0.0141 0.0141
>
> 2 0.0140 0.0142
>
> 4 0.0140 0.0141
>
> 8 0.0145 0.0140
>
> 16 0.0553 0.0168
>
> 32 0.1688 0.0549
>
> 64 0.5017 0.1690
>
> 128 1.7005 0.5038
>
> 256 5.2513 2.0804
>
> 512 8.0529 3.0162
>
>
>
> Cc: Andrew Morton <a...@linux-foundation.org>
>
> Cc: "Eric W. Biederman" <ebied...@xmission.com>
>
> Cc: Eric Dumazet <eric.duma...@gmail.com>
>
> Cc: Alexander Viro <v...@zeniv.linux.org.uk>
>
> Cc: David Woodhouse <dw...@infradead.org>
>
> Cc: Alexey Dobriyan <adobri...@gmail.com>
>
> Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
>
> Signed-off-by: Nathan Zimmer <nzim...@sgi.com>
>
> ---
>
> fs/proc/generic.c | 58 +++++++++---------
>
> fs/proc/inode.c | 156
> ++++++++++++++++++++++++++----------------------
>
> include/linux/proc_fs.h | 6 +-
>
> 3 files changed, 118 insertions(+), 102 deletions(-)
>
>
>
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
>
> index 76ddae8..6896a70 100644
>
> --- a/fs/proc/generic.c
>
> +++ b/fs/proc/generic.c
>
> @@ -191,13 +191,16 @@ proc_file_read(struct file *file, char __user *buf,
> size_t nbytes,
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> ssize_t rv = -EIO;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + const struct file_operations *fops;
>
> +
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + rcu_read_unlock();
>
>
>
> rv = __proc_file_read(file, buf, nbytes, ppos);
>
>
>
> @@ -213,13 +216,16 @@ proc_file_write(struct file *file, const char __user
> *buffer,
>
> ssize_t rv = -EIO;
>
>
>
> if (pde->write_proc) {
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + const struct file_operations *fops;
>
> +
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + rcu_read_unlock();
>
>
>
> /* FIXME: does this routine need ppos? probably... */
>
> rv = pde->write_proc(file, buffer, count, pde->data);
>
> @@ -558,7 +564,7 @@ static int proc_register(struct proc_dir_entry * dir,
> struct proc_dir_entry * dp
>
>
>
> if (S_ISDIR(dp->mode)) {
>
> if (dp->proc_iops == NULL) {
>
> - dp->proc_fops = &proc_dir_operations;
>
> + RCU_INIT_POINTER(dp->proc_fops, &proc_dir_operations);
>
> dp->proc_iops = &proc_dir_inode_operations;
>
> }
>
> dir->nlink++;
>
> @@ -567,7 +573,7 @@ static int proc_register(struct proc_dir_entry * dir,
> struct proc_dir_entry * dp
>
> dp->proc_iops = &proc_link_inode_operations;
>
> } else if (S_ISREG(dp->mode)) {
>
> if (dp->proc_fops == NULL)
>
> - dp->proc_fops = &proc_file_operations;
>
> + RCU_INIT_POINTER(dp->proc_fops, &proc_file_operations);
>
> if (dp->proc_iops == NULL)
>
> dp->proc_iops = &proc_file_inode_operations;
>
> }
>
> @@ -620,7 +626,8 @@ static struct proc_dir_entry *__proc_create(struct
> proc_dir_entry **parent,
>
> ent->mode = mode;
>
> ent->nlink = nlink;
>
> atomic_set(&ent->count, 1);
>
> - spin_lock_init(&ent->pde_unload_lock);
>
> + atomic_set(&ent->pde_users, 1);
>
> + spin_lock_init(&ent->pde_openers_lock);
>
> INIT_LIST_HEAD(&ent->pde_openers);
>
> out:
>
> return ent;
>
> @@ -744,7 +751,7 @@ struct proc_dir_entry *proc_create_data(const char *name,
> umode_t mode,
>
> pde = __proc_create(&parent, name, mode, nlink);
>
> if (!pde)
>
> goto out;
>
> - pde->proc_fops = proc_fops;
>
> + rcu_assign_pointer(pde->proc_fops, proc_fops);
>
> pde->data = data;
>
> if (proc_register(parent, pde) < 0)
>
> goto out_free;
>
> @@ -802,37 +809,30 @@ void remove_proc_entry(const char *name, struct
> proc_dir_entry *parent)
>
> return;
>
> }
>
>
>
> - spin_lock(&de->pde_unload_lock);
>
> /*
>
> * Stop accepting new callers into module. If you're
>
> * dynamically allocating ->proc_fops, save a pointer somewhere.
>
> */
>
> - de->proc_fops = NULL;
>
> - /* Wait until all existing callers into module are done. */
>
> - if (de->pde_users > 0) {
>
> - DECLARE_COMPLETION_ONSTACK(c);
>
> -
>
> - if (!de->pde_unload_completion)
>
> - de->pde_unload_completion = &c;
>
>
>
> - spin_unlock(&de->pde_unload_lock);
>
> + rcu_assign_pointer(de->proc_fops, NULL);
>
> + synchronize_rcu();
>
> + /* Wait until all existing callers into module are done. */
>
>
>
> + DECLARE_COMPLETION_ONSTACK(c);
>
> + de->pde_unload_completion = &c;
>
> + if (!atomic_dec_and_test(&de->pde_users))
>
> wait_for_completion(de->pde_unload_completion);
>
>
>
> - spin_lock(&de->pde_unload_lock);
>
> - }
>
> -
>
> + spin_lock(&de->pde_openers_lock);
>
> while (!list_empty(&de->pde_openers)) {
>
> struct pde_opener *pdeo;
>
>
>
> pdeo = list_first_entry(&de->pde_openers, struct pde_opener,
> lh);
>
> list_del(&pdeo->lh);
>
> - spin_unlock(&de->pde_unload_lock);
>
> pdeo->release(pdeo->inode, pdeo->file);
>
> kfree(pdeo);
>
> - spin_lock(&de->pde_unload_lock);
>
> }
>
> - spin_unlock(&de->pde_unload_lock);
>
> + spin_unlock(&de->pde_openers_lock);
>
>
>
> if (S_ISDIR(de->mode))
>
> parent->nlink--;
>
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
>
> index 439ae688..031af27 100644
>
> --- a/fs/proc/inode.c
>
> +++ b/fs/proc/inode.c
>
> @@ -128,46 +128,40 @@ static const struct super_operations proc_sops = {
>
> .show_options = proc_show_options,
>
> };
>
>
>
> -static void __pde_users_dec(struct proc_dir_entry *pde)
>
> -{
>
> - pde->pde_users--;
>
> - if (pde->pde_unload_completion && pde->pde_users == 0)
>
> - complete(pde->pde_unload_completion);
>
> -}
>
> -
>
> void pde_users_dec(struct proc_dir_entry *pde)
>
> {
>
> - spin_lock(&pde->pde_unload_lock);
>
> - __pde_users_dec(pde);
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + if (atomic_dec_and_test(&pde->pde_users) && pde->pde_unload_completion)
>
> + complete(pde->pde_unload_completion);
>
> }
>
>
>
> static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
>
> {
>
> + const struct file_operations *fops;
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> loff_t rv = -EINVAL;
>
> loff_t (*llseek)(struct file *, loff_t, int);
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> /*
>
> * remove_proc_entry() is going to delete PDE (as part of module
>
> * cleanup sequence). No new callers into module allowed.
>
> */
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> /*
>
> * Bump refcount so that remove_proc_entry will wail for ->llseek to
>
> * complete.
>
> */
>
> - pde->pde_users++;
>
> + atomic_inc(&pde->pde_users);
>
> /*
>
> * Save function pointer under lock, to protect against ->proc_fops
>
> * NULL'ifying right after ->pde_unload_lock is dropped.
>
> */
>
> - llseek = pde->proc_fops->llseek;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + llseek = fops->llseek;
>
> + rcu_read_unlock();
>
>
>
> if (!llseek)
>
> llseek = default_llseek;
>
> @@ -182,15 +176,17 @@ static ssize_t proc_reg_read(struct file *file, char
> __user *buf, size_t count,
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> ssize_t rv = -EIO;
>
> ssize_t (*read)(struct file *, char __user *, size_t, loff_t *);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - read = pde->proc_fops->read;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + read = fops->read;
>
> + rcu_read_unlock();
>
>
>
> if (read)
>
> rv = read(file, buf, count, ppos);
>
> @@ -204,15 +200,17 @@ static ssize_t proc_reg_write(struct file *file, const
> char __user *buf, size_t
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> ssize_t rv = -EIO;
>
> ssize_t (*write)(struct file *, const char __user *, size_t, loff_t *);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - write = pde->proc_fops->write;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + write = fops->write;
>
> + rcu_read_unlock();
>
>
>
> if (write)
>
> rv = write(file, buf, count, ppos);
>
> @@ -226,15 +224,17 @@ static unsigned int proc_reg_poll(struct file *file,
> struct poll_table_struct *p
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> unsigned int rv = DEFAULT_POLLMASK;
>
> unsigned int (*poll)(struct file *, struct poll_table_struct *);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - poll = pde->proc_fops->poll;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + poll = fops->poll;
>
> + rcu_read_unlock();
>
>
>
> if (poll)
>
> rv = poll(file, pts);
>
> @@ -248,15 +248,17 @@ static long proc_reg_unlocked_ioctl(struct file *file,
> unsigned int cmd, unsigne
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> long rv = -ENOTTY;
>
> long (*ioctl)(struct file *, unsigned int, unsigned long);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - ioctl = pde->proc_fops->unlocked_ioctl;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + ioctl = fops->unlocked_ioctl;
>
> + rcu_read_unlock();
>
>
>
> if (ioctl)
>
> rv = ioctl(file, cmd, arg);
>
> @@ -271,15 +273,17 @@ static long proc_reg_compat_ioctl(struct file *file,
> unsigned int cmd, unsigned
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> long rv = -ENOTTY;
>
> long (*compat_ioctl)(struct file *, unsigned int, unsigned long);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> + atomic_inc(&pde->pde_users);
>
> compat_ioctl = pde->proc_fops->compat_ioctl;
should this be compat_ioctl = fops->compat_ioctl ?
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_unlock();
>
>
>
> if (compat_ioctl)
>
> rv = compat_ioctl(file, cmd, arg);
>
> @@ -294,15 +298,17 @@ static int proc_reg_mmap(struct file *file, struct
> vm_area_struct *vma)
>
> struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
>
> int rv = -EIO;
>
> int (*mmap)(struct file *, struct vm_area_struct *);
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> + atomic_inc(&pde->pde_users);
>
> mmap = pde->proc_fops->mmap;
also for this, should it be compat_ioctl = fops->compat_ioctl ?
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_unlock();
>
>
>
> if (mmap)
>
> rv = mmap(file, vma);
>
> @@ -318,6 +324,7 @@ static int proc_reg_open(struct inode *inode, struct file
> *file)
>
> int (*open)(struct inode *, struct file *);
>
> int (*release)(struct inode *, struct file *);
>
> struct pde_opener *pdeo;
>
> + const struct file_operations *fops;
>
>
>
> /*
>
> * What for, you ask? Well, we can have open, rmmod, remove_proc_entry
>
> @@ -333,32 +340,33 @@ static int proc_reg_open(struct inode *inode, struct
> file *file)
>
> if (!pdeo)
>
> return -ENOMEM;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> - if (!pde->proc_fops) {
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> + rcu_read_unlock();
>
> kfree(pdeo);
>
> return -ENOENT;
>
> }
>
> - pde->pde_users++;
>
> - open = pde->proc_fops->open;
>
> - release = pde->proc_fops->release;
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + atomic_inc(&pde->pde_users);
>
> + open = fops->open;
>
> + release = fops->release;
>
> + rcu_read_lock();
>
>
>
> if (open)
>
> rv = open(inode, file);
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> if (rv == 0 && release) {
>
> /* To know what to release. */
>
> pdeo->inode = inode;
>
> pdeo->file = file;
>
> /* Strictly for "too late" ->release in proc_reg_release(). */
>
> pdeo->release = release;
>
> + spin_lock(&pde->pde_openers_lock);
>
> list_add(&pdeo->lh, &pde->pde_openers);
>
> + spin_unlock(&pde->pde_openers_lock);
>
> } else
>
> kfree(pdeo);
>
> - __pde_users_dec(pde);
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + pde_users_dec(pde);
>
> return rv;
>
> }
>
>
>
> @@ -367,10 +375,14 @@ static struct pde_opener *find_pde_opener(struct
> proc_dir_entry *pde,
>
> {
>
> struct pde_opener *pdeo;
>
>
>
> + spin_lock(&pde->pde_openers_lock);
>
> list_for_each_entry(pdeo, &pde->pde_openers, lh) {
>
> - if (pdeo->inode == inode && pdeo->file == file)
>
> + if (pdeo->inode == inode && pdeo->file == file) {
>
> + spin_unlock(&pde->pde_openers_lock);
>
> return pdeo;
>
> + }
>
> }
>
> + spin_unlock(&pde->pde_openers_lock);
>
> return NULL;
>
> }
>
>
>
> @@ -380,10 +392,12 @@ static int proc_reg_release(struct inode *inode, struct
> file *file)
>
> int rv = 0;
>
> int (*release)(struct inode *, struct file *);
>
> struct pde_opener *pdeo;
>
> + const struct file_operations *fops;
>
>
>
> - spin_lock(&pde->pde_unload_lock);
>
> pdeo = find_pde_opener(pde, inode, file);
>
> - if (!pde->proc_fops) {
>
> + rcu_read_lock();
>
> + fops = rcu_dereference(pde->proc_fops);
>
> + if (!fops) {
>
> /*
>
> * Can't simply exit, __fput() will think that everything is OK,
>
> * and move on to freeing struct file. remove_proc_entry() will
>
> @@ -393,21 +407,23 @@ static int proc_reg_release(struct inode *inode, struct
> file *file)
>
> * But if opener is removed from list, who will ->release it?
>
> */
>
> if (pdeo) {
>
> + spin_lock(&pde->pde_openers_lock);
>
> list_del(&pdeo->lh);
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + spin_unlock(&pde->pde_openers_lock);
>
> rv = pdeo->release(inode, file);
>
> kfree(pdeo);
>
> - } else
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + }
>
> return rv;
>
> }
>
> - pde->pde_users++;
>
> - release = pde->proc_fops->release;
>
> + atomic_inc(&pde->pde_users);
>
> + release = fops->release;
>
> + rcu_read_unlock();
>
> if (pdeo) {
>
> + spin_lock(&pde->pde_openers_lock);
>
> list_del(&pdeo->lh);
>
> - kfree(pdeo);
>
> + spin_unlock(&pde->pde_openers_lock);
>
> }
>
> - spin_unlock(&pde->pde_unload_lock);
>
> + kfree(pdeo);
>
>
>
> if (release)
>
> rv = release(inode, file);
>
> diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
>
> index 32676b3..82628d9 100644
>
> --- a/include/linux/proc_fs.h
>
> +++ b/include/linux/proc_fs.h
>
> @@ -68,16 +68,16 @@ struct proc_dir_entry {
>
> * If you're allocating ->proc_fops dynamically, save a pointer
>
> * somewhere.
>
> */
>
> - const struct file_operations *proc_fops;
>
> + const struct file_operations __rcu *proc_fops;
>
> struct proc_dir_entry *next, *parent, *subdir;
>
> void *data;
>
> read_proc_t *read_proc;
>
> write_proc_t *write_proc;
>
> atomic_t count; /* use count */
>
> - int pde_users; /* number of callers into module in progress */
>
> + atomic_t pde_users; /* number of callers into module in progress */
>
> struct completion *pde_unload_completion;
>
> + spinlock_t pde_openers_lock;
>
> struct list_head pde_openers; /* who did ->open, but not ->release */
>
> - spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
>
> u8 namelen;
>
> char name[];
>
> };
>
> --
>
> 1.8.1.2
>
>
>
> --
>
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