lockless get_write_access/deny_write_access (07b8ce1e) · Commits · github.com / kvm-riscv / linux

fs/namei.c

+0 −46

Original line number	Diff line number	Diff line
		@@ -341,52 +341,6 @@ static inline int exec_permission(struct inode *inode, unsigned int flags)
		return security_inode_exec_permission(inode, flags);
		}

		/*
		* get_write_access() gets write permission for a file.
		* put_write_access() releases this write permission.
		* This is used for regular files.
		* We cannot support write (and maybe mmap read-write shared) accesses and
		* MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
		* can have the following values:
		* 0: no writers, no VM_DENYWRITE mappings
		* < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
		* > 0: (i_writecount) users are writing to the file.
		*
		* Normally we operate on that counter with atomic_{inc,dec} and it's safe
		* except for the cases where we don't hold i_writecount yet. Then we need to
		* use {get,deny}_write_access() - these functions check the sign and refuse
		* to do the change if sign is wrong. Exclusion between them is provided by
		* the inode->i_lock spinlock.
		*/

		int get_write_access(struct inode * inode)
		{
		spin_lock(&inode->i_lock);
		if (atomic_read(&inode->i_writecount) < 0) {
		spin_unlock(&inode->i_lock);
		return -ETXTBSY;
		}
		atomic_inc(&inode->i_writecount);
		spin_unlock(&inode->i_lock);

		return 0;
		}

		int deny_write_access(struct file * file)
		{
		struct inode *inode = file->f_path.dentry->d_inode;

		spin_lock(&inode->i_lock);
		if (atomic_read(&inode->i_writecount) > 0) {
		spin_unlock(&inode->i_lock);
		return -ETXTBSY;
		}
		atomic_dec(&inode->i_writecount);
		spin_unlock(&inode->i_lock);

		return 0;
		}

		/**
		* path_get - get a reference to a path
		* @path: path to get the reference to

include/linux/atomic.h

+26 −0

Original line number	Diff line number	Diff line
		@@ -34,6 +34,32 @@ static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint)
		}
		#endif

		#ifndef atomic_inc_unless_negative
		static inline int atomic_inc_unless_negative(atomic_t *p)
		{
		int v, v1;
		for (v = 0; v >= 0; v = v1) {
		v1 = atomic_cmpxchg(p, v, v + 1);
		if (likely(v1 == v))
		return 1;
		}
		return 0;
		}
		#endif

		#ifndef atomic_dec_unless_positive
		static inline int atomic_dec_unless_positive(atomic_t *p)
		{
		int v, v1;
		for (v = 0; v <= 0; v = v1) {
		v1 = atomic_cmpxchg(p, v, v - 1);
		if (likely(v1 == v))
		return 1;
		}
		return 0;
		}
		#endif

		#ifndef CONFIG_ARCH_HAS_ATOMIC_OR
		static inline void atomic_or(int i, atomic_t *v)
		{

include/linux/fs.h

+26 −3

Original line number	Diff line number	Diff line
		@@ -392,8 +392,8 @@ struct inodes_stat_t {
		#include <linux/semaphore.h>
		#include <linux/fiemap.h>
		#include <linux/rculist_bl.h>
		#include <linux/atomic.h>

		#include <asm/atomic.h>
		#include <asm/byteorder.h>

		struct export_operations;
		@@ -2195,8 +2195,31 @@ static inline bool execute_ok(struct inode *inode)
		return (inode->i_mode & S_IXUGO) \|\| S_ISDIR(inode->i_mode);
		}

		extern int get_write_access(struct inode *);
		extern int deny_write_access(struct file *);
		/*
		* get_write_access() gets write permission for a file.
		* put_write_access() releases this write permission.
		* This is used for regular files.
		* We cannot support write (and maybe mmap read-write shared) accesses and
		* MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
		* can have the following values:
		* 0: no writers, no VM_DENYWRITE mappings
		* < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
		* > 0: (i_writecount) users are writing to the file.
		*
		* Normally we operate on that counter with atomic_{inc,dec} and it's safe
		* except for the cases where we don't hold i_writecount yet. Then we need to
		* use {get,deny}_write_access() - these functions check the sign and refuse
		* to do the change if sign is wrong.
		*/
		static inline int get_write_access(struct inode *inode)
		{
		return atomic_inc_unless_negative(&inode->i_writecount) ? 0 : -ETXTBSY;
		}
		static inline int deny_write_access(struct file *file)
		{
		struct inode *inode = file->f_path.dentry->d_inode;
		return atomic_dec_unless_positive(&inode->i_writecount) ? 0 : -ETXTBSY;
		}
		static inline void put_write_access(struct inode * inode)
		{
		atomic_dec(&inode->i_writecount);