Commit d810d4c2 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

fs/pipe: do not open-code pipe head/tail logic in FIONREAD 



Rasmus points out that we do indeed have other cases of breakage from
the type changes that were introduced on 32-bit targets in order to read
the pipe head and tail values atomically (commit 3d252160: "fs/pipe:
Read pipe->{head,tail} atomically outside pipe->mutex").

Fix it up by using the proper helper functions that now deal with the
pipe buffer index types properly.  This makes the code simpler and more
obvious.

The compiler does the CSE and loop hoisting of the pipe ring size
masking that we used to do manually, so open-coding this was never a
good idea.

Reported-by: default avatarRasmus Villemoes <ravi@prevas.dk>
Link: https://lore.kernel.org/all/87cyeu5zgk.fsf@prevas.dk/


Fixes: 3d252160 ("fs/pipe: Read pipe->{head,tail} atomically outside pipe->mutex")Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Swapnil Sapkal <swapnil.sapkal@amd.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 74d42bdb

fs/pipe.c

+3 −4
Original line number Diff line number Diff line
@@ -614,7 +614,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) 
static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

{

	struct pipe_inode_info *pipe = filp->private_data;

	unsigned int count, head, tail, mask;

	unsigned int count, head, tail;



	switch (cmd) {

	case FIONREAD:
@@ -622,10 +622,9 @@ static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 
		count = 0;

		head = pipe->head;

		tail = pipe->tail;

		mask = pipe->ring_size - 1;



		while (tail != head) {

			count += pipe->bufs[tail & mask].len;

		while (!pipe_empty(head, tail)) {

			count += pipe_buf(pipe, tail)->len;

			tail++;

		}

		mutex_unlock(&pipe->mutex);