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-rw-r--r--fs/read_write.c54
1 files changed, 40 insertions, 14 deletions
diff --git a/fs/read_write.c b/fs/read_write.c
index edc5746..932bb34 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -264,10 +264,36 @@ loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
}
EXPORT_SYMBOL(vfs_llseek);
+/*
+ * We only lock f_pos if we have threads or if the file might be
+ * shared with another process. In both cases we'll have an elevated
+ * file count (done either by fdget() or by fork()).
+ */
+static inline struct fd fdget_pos(int fd)
+{
+ struct fd f = fdget(fd);
+ struct file *file = f.file;
+
+ if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
+ if (file_count(file) > 1) {
+ f.flags |= FDPUT_POS_UNLOCK;
+ mutex_lock(&file->f_pos_lock);
+ }
+ }
+ return f;
+}
+
+static inline void fdput_pos(struct fd f)
+{
+ if (f.flags & FDPUT_POS_UNLOCK)
+ mutex_unlock(&f.file->f_pos_lock);
+ fdput(f);
+}
+
SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
{
off_t retval;
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
if (!f.file)
return -EBADF;
@@ -278,7 +304,7 @@ SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
if (res != (loff_t)retval)
retval = -EOVERFLOW; /* LFS: should only happen on 32 bit platforms */
}
- fdput(f);
+ fdput_pos(f);
return retval;
}
@@ -498,7 +524,7 @@ static inline void file_pos_write(struct file *file, loff_t pos)
SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret = -EBADF;
if (f.file) {
@@ -506,7 +532,7 @@ SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
ret = vfs_read(f.file, buf, count, &pos);
if (ret >= 0)
file_pos_write(f.file, pos);
- fdput(f);
+ fdput_pos(f);
}
return ret;
}
@@ -514,7 +540,7 @@ SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
size_t, count)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret = -EBADF;
if (f.file) {
@@ -522,7 +548,7 @@ SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
ret = vfs_write(f.file, buf, count, &pos);
if (ret >= 0)
file_pos_write(f.file, pos);
- fdput(f);
+ fdput_pos(f);
}
return ret;
@@ -797,7 +823,7 @@ EXPORT_SYMBOL(vfs_writev);
SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
unsigned long, vlen)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret = -EBADF;
if (f.file) {
@@ -805,7 +831,7 @@ SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
ret = vfs_readv(f.file, vec, vlen, &pos);
if (ret >= 0)
file_pos_write(f.file, pos);
- fdput(f);
+ fdput_pos(f);
}
if (ret > 0)
@@ -817,7 +843,7 @@ SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
unsigned long, vlen)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret = -EBADF;
if (f.file) {
@@ -825,7 +851,7 @@ SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
ret = vfs_writev(f.file, vec, vlen, &pos);
if (ret >= 0)
file_pos_write(f.file, pos);
- fdput(f);
+ fdput_pos(f);
}
if (ret > 0)
@@ -968,7 +994,7 @@ COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
const struct compat_iovec __user *,vec,
compat_ulong_t, vlen)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret;
loff_t pos;
@@ -978,7 +1004,7 @@ COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
ret = compat_readv(f.file, vec, vlen, &pos);
if (ret >= 0)
f.file->f_pos = pos;
- fdput(f);
+ fdput_pos(f);
return ret;
}
@@ -1035,7 +1061,7 @@ COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
const struct compat_iovec __user *, vec,
compat_ulong_t, vlen)
{
- struct fd f = fdget(fd);
+ struct fd f = fdget_pos(fd);
ssize_t ret;
loff_t pos;
@@ -1045,7 +1071,7 @@ COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
ret = compat_writev(f.file, vec, vlen, &pos);
if (ret >= 0)
f.file->f_pos = pos;
- fdput(f);
+ fdput_pos(f);
return ret;
}
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