Re: [PATCH 2/2] debugfs: prevent access to removed files' private data

Paul E. McKenney
2015-12-01T18:05:36Z

On Tue, Dec 01, 2015 at 12:26:41AM +0100, Nicolai Stange wrote:
> Upon return of debugfs_remove()/debugfs_remove_recursive(), it might
> still be attempted to access associated private file data through
> previously opened struct file objects. If that data has been freed by
> the caller of debugfs_remove*() in the meanwhile, the reading/writing
> process would either encounter a fault or, if the memory address in
> question has been reassigned again, unrelated data structures could get
> overwritten.
>
> However, since debugfs files are seldomly removed, usually from module
> exit handlers only, the impact is very low.
>
> Since debugfs_remove() and debugfs_remove_recursive() are already
> waiting for a SRCU grace period before returning to their callers,
> enclosing the access to private file data from ->read() and ->write()
> within a SRCU read-side critical section does the trick:
> - Introduce the debugfs_file_use_data_start() and
> debugfs_file_use_data_finish() helpers which just enter and leave
> a SRCU read-side critical section. The former also reports whether the
> file is still alive, that is if d_delete() has _not_ been called on
> the corresponding dentry.
> - Introduce the DEFINE_DEBUGFS_ATTRIBUTE() macro which is completely
> equivalent to the DEFINE_SIMPLE_ATTRIBUTE() macro except that
> ->read() and ->write are set to SRCU protecting wrappers around the
> original simple_read() and simple_write() helpers.
> - Use that DEFINE_DEBUGFS_ATTRIBUTE() macro for all debugfs_create_*()
> attribute creation variants where appropriate.
> - Manually introduce SRCU protection to the debugfs-predefined readers
> and writers not covered by the above DEFINE_SIMPLE_ATTRIBUTE()->
> DEFINE_DEBUGFS_ATTRIBUTE() replacement.
>
> Finally, it should be worth to note that in the vast majority of cases
> where debugfs users are handing in a "custom" struct file_operations
> object to debugfs_create_file(), an attribute's associated data's
> lifetime is bound to the one of the containing module and thus,
> taking a reference on ->owner during file opening acts as a proxy here.
> There is no need to do a mass replace of DEFINE_SIMPLE_ATTRIBUTE() to
> DEFINE_DEBUGFS_ATTRIBUTE() outside of debugfs.
>
> Signed-off-by: Nicolai Stange <nicstange@gmail.com>

Also looks good from an RCU perspective.

Thanx, Paul

> ---
> Applicable to the Linus tree.
> The second of the two patches depends on the first one
>
> Documentation/DocBook/filesystems.tmpl | 1 +
> fs/debugfs/file.c | 185 +++++++++++++++++++++++++--------
> fs/debugfs/inode.c | 1 +
> include/linux/debugfs.h | 66 ++++++++++++
> 4 files changed, 209 insertions(+), 44 deletions(-)
>
> diff --git a/Documentation/DocBook/filesystems.tmpl b/Documentation/DocBook/filesystems.tmpl
> index 6006b63..1f2f6c0 100644
> --- a/Documentation/DocBook/filesystems.tmpl
> +++ b/Documentation/DocBook/filesystems.tmpl
> @@ -99,6 +99,7 @@
> <sect1 id="debugfs_interface"> debugfs interface
> !Efs/debugfs/inode.c
> !Efs/debugfs/file.c
> +!Iinclude/linux/debugfs.h
> </sect1>
> </chapter>
>
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index 67df2c9..8e10695 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -69,6 +69,45 @@ const struct file_operations debugfs_proxy_file_operations = {
> .open = proxy_open,
> };
>
> +int __debugfs_file_use_data_start(struct file *file, int *srcu_idx)
> + __acquires(&debugfs_srcu)
> +{
> + *srcu_idx = srcu_read_lock(&debugfs_srcu);
> + if (d_unlinked(file->f_path.dentry))
> + return -EIO;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(__debugfs_file_use_data_start);
> +
> +ssize_t debugfs_attr_read(struct file *file, char __user *buf,
> + size_t len, loff_t *ppos)
> +{
> + ssize_t ret;
> + int srcu_idx;
> +
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (!ret)
> + ret = simple_attr_read(file, buf, len, ppos);
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(debugfs_attr_read);
> +
> +ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
> + size_t len, loff_t *ppos)
> +{
> + ssize_t ret;
> + int srcu_idx;
> +
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (!ret)
> + ret = simple_attr_write(file, buf, len, ppos);
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(debugfs_attr_write);
> +
> static struct dentry *debugfs_create_mode(const char *name, umode_t mode,
> struct dentry *parent, void *value,
> const struct file_operations *fops,
> @@ -95,9 +134,9 @@ static int debugfs_u8_get(void *data, u64 *val)
> *val = *(u8 *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u8_ro, debugfs_u8_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u8_wo, NULL, debugfs_u8_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u8_ro, debugfs_u8_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u8_wo, NULL, debugfs_u8_set, "%llu\n");
>
> /**
> * debugfs_create_u8 - create a debugfs file that is used to read and write an unsigned 8-bit value
> @@ -141,9 +180,9 @@ static int debugfs_u16_get(void *data, u64 *val)
> *val = *(u16 *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u16_ro, debugfs_u16_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u16_wo, NULL, debugfs_u16_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u16_ro, debugfs_u16_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u16_wo, NULL, debugfs_u16_set, "%llu\n");
>
> /**
> * debugfs_create_u16 - create a debugfs file that is used to read and write an unsigned 16-bit value
> @@ -187,9 +226,9 @@ static int debugfs_u32_get(void *data, u64 *val)
> *val = *(u32 *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u32_ro, debugfs_u32_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u32_wo, NULL, debugfs_u32_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u32_ro, debugfs_u32_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u32_wo, NULL, debugfs_u32_set, "%llu\n");
>
> /**
> * debugfs_create_u32 - create a debugfs file that is used to read and write an unsigned 32-bit value
> @@ -234,9 +273,9 @@ static int debugfs_u64_get(void *data, u64 *val)
> *val = *(u64 *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u64, debugfs_u64_get, debugfs_u64_set, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u64_ro, debugfs_u64_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_u64_wo, NULL, debugfs_u64_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u64, debugfs_u64_get, debugfs_u64_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u64_ro, debugfs_u64_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_u64_wo, NULL, debugfs_u64_set, "%llu\n");
>
> /**
> * debugfs_create_u64 - create a debugfs file that is used to read and write an unsigned 64-bit value
> @@ -281,9 +320,10 @@ static int debugfs_ulong_get(void *data, u64 *val)
> *val = *(unsigned long *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_ulong, debugfs_ulong_get, debugfs_ulong_set, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_ulong_ro, debugfs_ulong_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_ulong_wo, NULL, debugfs_ulong_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_ulong, debugfs_ulong_get, debugfs_ulong_set,
> + "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_ulong_ro, debugfs_ulong_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_ulong_wo, NULL, debugfs_ulong_set, "%llu\n");
>
> /**
> * debugfs_create_ulong - create a debugfs file that is used to read and write
> @@ -318,21 +358,24 @@ struct dentry *debugfs_create_ulong(const char *name, umode_t mode,
> }
> EXPORT_SYMBOL_GPL(debugfs_create_ulong);
>
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x8, debugfs_u8_get, debugfs_u8_set, "0x%02llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x8_ro, debugfs_u8_get, NULL, "0x%02llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x8_wo, NULL, debugfs_u8_set, "0x%02llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x8, debugfs_u8_get, debugfs_u8_set, "0x%02llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x8_ro, debugfs_u8_get, NULL, "0x%02llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x8_wo, NULL, debugfs_u8_set, "0x%02llx\n");
>
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x16, debugfs_u16_get, debugfs_u16_set, "0x%04llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x16_ro, debugfs_u16_get, NULL, "0x%04llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x16_wo, NULL, debugfs_u16_set, "0x%04llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x16, debugfs_u16_get, debugfs_u16_set,
> + "0x%04llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x16_ro, debugfs_u16_get, NULL, "0x%04llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x16_wo, NULL, debugfs_u16_set, "0x%04llx\n");
>
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x32, debugfs_u32_get, debugfs_u32_set, "0x%08llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x32_ro, debugfs_u32_get, NULL, "0x%08llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x32_wo, NULL, debugfs_u32_set, "0x%08llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x32, debugfs_u32_get, debugfs_u32_set,
> + "0x%08llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x32_ro, debugfs_u32_get, NULL, "0x%08llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x32_wo, NULL, debugfs_u32_set, "0x%08llx\n");
>
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x64, debugfs_u64_get, debugfs_u64_set, "0x%016llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x64_ro, debugfs_u64_get, NULL, "0x%016llx\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_x64_wo, NULL, debugfs_u64_set, "0x%016llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x64, debugfs_u64_get, debugfs_u64_set,
> + "0x%016llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x64_ro, debugfs_u64_get, NULL, "0x%016llx\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_x64_wo, NULL, debugfs_u64_set, "0x%016llx\n");
>
> /*
> * debugfs_create_x{8,16,32,64} - create a debugfs file that is used to read and write an unsigned {8,16,32,64}-bit value
> @@ -425,10 +468,10 @@ static int debugfs_size_t_get(void *data, u64 *val)
> *val = *(size_t *)data;
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_size_t, debugfs_size_t_get, debugfs_size_t_set,
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_size_t, debugfs_size_t_get, debugfs_size_t_set,
> "%llu\n"); /* %llu and %zu are more or less the same */
> -DEFINE_SIMPLE_ATTRIBUTE(fops_size_t_ro, debugfs_size_t_get, NULL, "%llu\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_size_t_wo, NULL, debugfs_size_t_set, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_size_t_ro, debugfs_size_t_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_size_t_wo, NULL, debugfs_size_t_set, "%llu\n");
>
> /**
> * debugfs_create_size_t - create a debugfs file that is used to read and write an size_t value
> @@ -458,10 +501,12 @@ static int debugfs_atomic_t_get(void *data, u64 *val)
> *val = atomic_read((atomic_t *)data);
> return 0;
> }
> -DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
> debugfs_atomic_t_set, "%lld\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL, "%lld\n");
> -DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set, "%lld\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL,
> + "%lld\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set,
> + "%lld\n");
>
> /**
> * debugfs_create_atomic_t - create a debugfs file that is used to read and
> @@ -487,11 +532,18 @@ ssize_t debugfs_read_file_bool(struct file *file, char __user *user_buf,
> {
> char buf[3];
> bool *val = file->private_data;
> + int ret, srcu_idx;
>
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (ret) {
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> + }
> if (*val)
> buf[0] = 'Y';
> else
> buf[0] = 'N';
> + debugfs_file_use_data_finish(srcu_idx);
> buf[1] = '\n';
> buf[2] = 0x00;
> return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
> @@ -505,16 +557,26 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
> size_t buf_size;
> bool bv;
> bool *val = file->private_data;
> + ssize_t ret;
> + int srcu_idx;
>
> buf_size = min(count, (sizeof(buf)-1));
> if (copy_from_user(buf, user_buf, buf_size))
> return -EFAULT;
>
> buf[buf_size] = '\0';
> - if (strtobool(buf, &bv) == 0)
> - *val = bv;
> + if (strtobool(buf, &bv) == 0) {
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (!ret) {
> + *val = bv;
> + ret = count;
> + }
> + debugfs_file_use_data_finish(srcu_idx);
> + } else {
> + return -EINVAL;
> + }
>
> - return count;
> + return ret;
> }
> EXPORT_SYMBOL_GPL(debugfs_write_file_bool);
>
> @@ -572,9 +634,16 @@ EXPORT_SYMBOL_GPL(debugfs_create_bool);
> static ssize_t read_file_blob(struct file *file, char __user *user_buf,
> size_t count, loff_t *ppos)
> {
> + ssize_t ret;
> + int srcu_idx;
> struct debugfs_blob_wrapper *blob = file->private_data;
> - return simple_read_from_buffer(user_buf, count, ppos, blob->data,
> - blob->size);
> +
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (!ret)
> + ret = simple_read_from_buffer(user_buf, count, ppos, blob->data,
> + blob->size);
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> }
>
> static const struct file_operations fops_blob = {
> @@ -643,6 +712,7 @@ static int u32_array_open(struct inode *inode, struct file *file)
> struct array_data *data = inode->i_private;
> int size, elements = data->elements;
> char *buf;
> + int ret, srcu_idx;
>
> /*
> * Max size:
> @@ -656,9 +726,17 @@ static int u32_array_open(struct inode *inode, struct file *file)
> buf[size] = 0;
>
> file->private_data = buf;
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (ret) {
> + kfree(file->private_data);
> + goto out;
> + }
> u32_format_array(buf, size, data->array, data->elements);
> + nonseekable_open(inode, file);
>
> - return nonseekable_open(inode, file);
> +out:
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> }
>
> static ssize_t u32_array_read(struct file *file, char __user *buf, size_t len,
> @@ -761,15 +839,21 @@ EXPORT_SYMBOL_GPL(debugfs_print_regs32);
>
> static int debugfs_show_regset32(struct seq_file *s, void *data)
> {
> - struct debugfs_regset32 *regset = s->private;
> + struct file *f = s->private;
> + struct debugfs_regset32 *regset = file_inode(f)->i_private;
> + int ret, srcu_idx;
>
> - debugfs_print_regs32(s, regset->regs, regset->nregs, regset->base, "");
> - return 0;
> + ret = debugfs_file_use_data_start(f, &srcu_idx);
> + if (!ret)
> + debugfs_print_regs32(s, regset->regs, regset->nregs,
> + regset->base, "");
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> }
>
> static int debugfs_open_regset32(struct inode *inode, struct file *file)
> {
> - return single_open(file, debugfs_show_regset32, inode->i_private);
> + return single_open(file, debugfs_show_regset32, file);
> }
>
> static const struct file_operations fops_regset32 = {
> @@ -826,11 +910,24 @@ static int debugfs_devm_entry_open(struct inode *inode, struct file *f)
> return single_open(f, entry->read, entry->dev);
> }
>
> +static ssize_t debugfs_devm_entry_read(struct file *file, char __user *buf,
> + size_t size, loff_t *ppos)
> +{
> + ssize_t ret;
> + int srcu_idx;
> +
> + ret = debugfs_file_use_data_start(file, &srcu_idx);
> + if (!ret)
> + ret = seq_read(file, buf, size, ppos);
> + debugfs_file_use_data_finish(srcu_idx);
> + return ret;
> +}
> +
> static const struct file_operations debugfs_devm_entry_ops = {
> .owner = THIS_MODULE,
> .open = debugfs_devm_entry_open,
> .release = single_release,
> - .read = seq_read,
> + .read = debugfs_devm_entry_read,
> .llseek = seq_lseek
> };
>
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 8ae2e1a..37222c9 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -31,6 +31,7 @@
> #define DEBUGFS_DEFAULT_MODE 0700
>
> DEFINE_SRCU(debugfs_srcu);
> +EXPORT_SYMBOL_GPL(debugfs_srcu);
>
> static struct vfsmount *debugfs_mount;
> static int debugfs_mount_count;
> diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
> index f8c7494..ba1a299 100644
> --- a/include/linux/debugfs.h
> +++ b/include/linux/debugfs.h
> @@ -20,6 +20,7 @@
>
> #include <linux/types.h>
> #include <linux/srcu.h>
> +#include <linux/compiler.h>
>
> struct device;
> struct file_operations;
> @@ -128,6 +129,71 @@ ssize_t debugfs_read_file_bool(struct file *file, char __user *user_buf,
> ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
> size_t count, loff_t *ppos);
>
> +int __debugfs_file_use_data_start(struct file *file, int *srcu_idx)
> + __acquires(&debugfs_srcu);
> +
> +/**
> + * debugfs_file_use_data_start - mark the beginning of file data access
> + * @file: the file object whose data is being accessed.
> + * @srcu_idx: a pointer to some memory to store a SRCU index in.
> + *
> + * Up to a matching call to debugfs_file_use_data_finish(), any
> + * successive call into the file removing functions debugfs_remove()
> + * and debugfs_remove_recursive() will block. Since associated private
> + * file data may only get freed after a successful return of any of
> + * the removal functions, you may safely access it after a successful
> + * call to debugfs_file_use_data_start() without worrying about
> + * lifetime issues.
> + *
> + * If -%EIO is returned, the file has already been removed and thus,
> + * it is not safe to access any of its data. If, on the other hand,
> + * it is allowed to access the file data, zero is returned.
> + *
> + * Regardless of the return code, any call to
> + * debugfs_file_use_data_start() must be followed by a matching call
> + * to debugfs_file_use_data_finish().
> + */
> +static inline int debugfs_file_use_data_start(struct file *file, int *srcu_idx)
> + __acquires(&debugfs_srcu)
> +{
> + return __debugfs_file_use_data_start(file, srcu_idx);
> +}
> +
> +/**
> + * debugfs_file_use_data_finish - mark the end of file data access
> + * @srcu_idx: the SRCU index "created" by a former call to
> + * debugfs_file_use_data_start().
> + *
> + * Allow any ongoing concurrent call into debugfs_remove() or
> + * debugfs_remove_recursive() blocked by a former call to
> + * debugfs_file_use_data_start() to proceed and return to its caller.
> + */
> +static inline void debugfs_file_use_data_finish(int srcu_idx)
> + __releases(&debugfs_srcu)
> +{
> + srcu_read_unlock(&debugfs_srcu, srcu_idx);
> +}
> +
> +ssize_t debugfs_attr_read(struct file *file, char __user *buf,
> + size_t len, loff_t *ppos);
> +ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
> + size_t len, loff_t *ppos);
> +
> +#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \
> +static int __fops ## _open(struct inode *inode, struct file *file) \
> +{ \
> + __simple_attr_check_format(__fmt, 0ull); \
> + return simple_attr_open(inode, file, __get, __set, __fmt); \
> +} \
> +static const struct file_operations __fops = { \
> + .owner = THIS_MODULE, \
> + .open = __fops ## _open, \
> + .release = simple_attr_release, \
> + .read = debugfs_attr_read, \
> + .write = debugfs_attr_write, \
> + .llseek = generic_file_llseek, \
> +}
> +
> #else
>
> #include <linux/err.h>
> --
> 2.6.3
>