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bcachefs: thread_with_stdio: eliminate double buffering 

The output buffer lock has to be a spinlock so that we can write to it
from interrupt context, so we can't use a direct copy_to_user; this
switches thread_with_file_read() to use fault_in_writeable() and
copy_to_user_nofault(), similar to how thread_with_file_write() works.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-02-04 20:19:49 -05:00
parent cb6fc943b6
commit e017047fdb
2 changed files with 17 additions and 40 deletions
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56
fs/bcachefs/thread_with_file.c
View File

@ -67,16 +67,15 @@ err:
static inline bool thread_with_stdio_has_output(struct thread_with_stdio *thr)
{
return thr->stdio.output_buf.pos ||
thr->output2.nr ||
thr->thr.done;
return thr->stdio.output_buf.pos || thr->thr.done;
}
static ssize_t thread_with_stdio_read(struct file *file, char __user *buf,
static ssize_t thread_with_stdio_read(struct file *file, char __user *ubuf,
size_t len, loff_t *ppos)
{
struct thread_with_stdio *thr =
container_of(file->private_data, struct thread_with_stdio, thr);
struct printbuf *buf = &thr->stdio.output_buf;
size_t copied = 0, b;
int ret = 0;
@ -89,44 +88,25 @@ static ssize_t thread_with_stdio_read(struct file *file, char __user *buf,
if (ret)
return ret;
if (thr->thr.done)
return 0;
while (len) {
ret = darray_make_room(&thr->output2, thr->stdio.output_buf.pos);
if (ret)
break;
spin_lock_irq(&thr->stdio.output_lock);
b = min_t(size_t, darray_room(thr->output2), thr->stdio.output_buf.pos);
memcpy(&darray_top(thr->output2), thr->stdio.output_buf.buf, b);
memmove(thr->stdio.output_buf.buf,
thr->stdio.output_buf.buf + b,
thr->stdio.output_buf.pos - b);
thr->output2.nr += b;
thr->stdio.output_buf.pos -= b;
spin_unlock_irq(&thr->stdio.output_lock);
b = min(len, thr->output2.nr);
if (!b)
break;
b -= copy_to_user(buf, thr->output2.data, b);
if (!b) {
while (len && buf->pos) {
if (fault_in_writeable(ubuf, len) == len) {
ret = -EFAULT;
break;
}
copied += b;
buf += b;
len -= b;
spin_lock_irq(&thr->stdio.output_lock);
b = min_t(size_t, len, buf->pos);
memmove(thr->output2.data,
thr->output2.data + b,
thr->output2.nr - b);
thr->output2.nr -= b;
if (b && !copy_to_user_nofault(ubuf, buf->buf, b)) {
memmove(buf->buf,
buf->buf + b,
buf->pos - b);
buf->pos -= b;
ubuf += b;
len -= b;
copied += b;
}
spin_unlock_irq(&thr->stdio.output_lock);
}
return copied ?: ret;
@ -140,7 +120,6 @@ static int thread_with_stdio_release(struct inode *inode, struct file *file)
bch2_thread_with_file_exit(&thr->thr);
printbuf_exit(&thr->stdio.input_buf);
printbuf_exit(&thr->stdio.output_buf);
darray_exit(&thr->output2);
thr->exit(thr);
return 0;
}
@ -245,7 +224,6 @@ int bch2_run_thread_with_stdio(struct thread_with_stdio *thr,
spin_lock_init(&thr->stdio.output_lock);
init_waitqueue_head(&thr->stdio.output_wait);
darray_init(&thr->output2);
thr->exit = exit;
return bch2_run_thread_with_file(&thr->thr, &thread_with_stdio_fops, fn);

1
fs/bcachefs/thread_with_file.h
View File

@ -20,7 +20,6 @@ int bch2_run_thread_with_file(struct thread_with_file *,
struct thread_with_stdio {
struct thread_with_file thr;
struct stdio_redirect stdio;
DARRAY(char) output2;
void (*exit)(struct thread_with_stdio *);
};