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SubjectRe: [PATCH 0/2] pipe: Fixes [ver #2]
On Wed, Dec 18, 2019 at 04:03:18PM -0800, Josh Triplett wrote:
> On Wed, Dec 18, 2019 at 02:51:27PM -0800, Linus Torvalds wrote:
> > That's my latest version, but you'll have to tweak it a tiny bit
> > because of d1c6a2aa02af ("pipe: simplify signal handling in
> > pipe_read() and add comments") which I did after that patch.
>
> That's what I encountered, and I ended up manually fixing it up,
> resulting in the attached patch. Does that look reasonable?

Er, wrong file. That's the original patch; the attached patch is the
right one.
diff --git a/fs/coredump.c b/fs/coredump.c
index b1ea7dfbd149..f8296a82d01d 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -517,7 +517,7 @@ static void wait_for_dump_helpers(struct file *file)
pipe_lock(pipe);
pipe->readers++;
pipe->writers--;
- wake_up_interruptible_sync(&pipe->wait);
+ wake_up_interruptible_sync(&pipe->rd_wait);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
pipe_unlock(pipe);

@@ -525,7 +525,7 @@ static void wait_for_dump_helpers(struct file *file)
* We actually want wait_event_freezable() but then we need
* to clear TIF_SIGPENDING and improve dump_interrupted().
*/
- wait_event_interruptible(pipe->wait, pipe->readers == 1);
+ wait_event_interruptible(pipe->rd_wait, pipe->readers == 1);

pipe_lock(pipe);
pipe->readers--;
diff --git a/fs/pipe.c b/fs/pipe.c
index 04d004ee2e8c..5ca6446ca2b1 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -108,16 +108,19 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe)
{
- DEFINE_WAIT(wait);
+ DEFINE_WAIT(rdwait);
+ DEFINE_WAIT(wrwait);

/*
* Pipes are system-local resources, so sleeping on them
* is considered a noninteractive wait:
*/
- prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
+ prepare_to_wait(&pipe->rd_wait, &rdwait, TASK_INTERRUPTIBLE);
+ prepare_to_wait(&pipe->wr_wait, &wrwait, TASK_INTERRUPTIBLE);
pipe_unlock(pipe);
schedule();
- finish_wait(&pipe->wait, &wait);
+ finish_wait(&pipe->rd_wait, &rdwait);
+ finish_wait(&pipe->wr_wait, &wrwait);
pipe_lock(pipe);
}

@@ -286,7 +289,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
size_t total_len = iov_iter_count(to);
struct file *filp = iocb->ki_filp;
struct pipe_inode_info *pipe = filp->private_data;
- bool was_full;
+ bool was_full, wake_next_reader = false;
ssize_t ret;

/* Null read succeeds. */
@@ -344,10 +347,10 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)

if (!buf->len) {
pipe_buf_release(pipe, buf);
- spin_lock_irq(&pipe->wait.lock);
+ spin_lock_irq(&pipe->rd_wait.lock);
tail++;
pipe->tail = tail;
- spin_unlock_irq(&pipe->wait.lock);
+ spin_unlock_irq(&pipe->rd_wait.lock);
}
total_len -= chars;
if (!total_len)
@@ -384,7 +387,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
* no data.
*/
if (unlikely(was_full)) {
- wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
+ wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}

@@ -394,18 +397,23 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
* since we've done any required wakeups and there's no need
* to mark anything accessed. And we've dropped the lock.
*/
- if (wait_event_interruptible(pipe->wait, pipe_readable(pipe)) < 0)
+ if (wait_event_interruptible_exclusive(pipe->rd_wait, pipe_readable(pipe)) < 0)
return -ERESTARTSYS;

__pipe_lock(pipe);
was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
+ wake_next_reader = true;
}
+ if (pipe_empty(pipe->head, pipe->tail))
+ wake_next_reader = false;
__pipe_unlock(pipe);

if (was_full) {
- wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM);
+ wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}
+ if (wake_next_reader)
+ wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
if (ret > 0)
file_accessed(filp);
return ret;
@@ -437,6 +445,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
size_t total_len = iov_iter_count(from);
ssize_t chars;
bool was_empty = false;
+ bool wake_next_writer = false;

/* Null write succeeds. */
if (unlikely(total_len == 0))
@@ -515,16 +524,16 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
* it, either the reader will consume it or it'll still
* be there for the next write.
*/
- spin_lock_irq(&pipe->wait.lock);
+ spin_lock_irq(&pipe->rd_wait.lock);

head = pipe->head;
if (pipe_full(head, pipe->tail, pipe->max_usage)) {
- spin_unlock_irq(&pipe->wait.lock);
+ spin_unlock_irq(&pipe->rd_wait.lock);
continue;
}

pipe->head = head + 1;
- spin_unlock_irq(&pipe->wait.lock);
+ spin_unlock_irq(&pipe->rd_wait.lock);

/* Insert it into the buffer array */
buf = &pipe->bufs[head & mask];
@@ -576,14 +585,17 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
*/
__pipe_unlock(pipe);
if (was_empty) {
- wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
+ wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}
- wait_event_interruptible(pipe->wait, pipe_writable(pipe));
+ wait_event_interruptible_exclusive(pipe->wr_wait, pipe_writable(pipe));
__pipe_lock(pipe);
was_empty = pipe_empty(head, pipe->tail);
+ wake_next_writer = true;
}
out:
+ if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
+ wake_next_writer = false;
__pipe_unlock(pipe);

/*
@@ -596,9 +608,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
* wake up pending jobs
*/
if (was_empty) {
- wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLRDNORM);
+ wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}
+ if (wake_next_writer)
+ wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM);
if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
int err = file_update_time(filp);
if (err)
@@ -642,12 +656,15 @@ pipe_poll(struct file *filp, poll_table *wait)
unsigned int head, tail;

/*
- * Reading only -- no need for acquiring the semaphore.
+ * Reading pipe state only -- no need for acquiring the semaphore.
*
* But because this is racy, the code has to add the
* entry to the poll table _first_ ..
*/
- poll_wait(filp, &pipe->wait, wait);
+ if (filp->f_mode & FMODE_READ)
+ poll_wait(filp, &pipe->rd_wait, wait);
+ if (filp->f_mode & FMODE_WRITE)
+ poll_wait(filp, &pipe->wr_wait, wait);

/*
* .. and only then can you do the racy tests. That way,
@@ -706,7 +723,8 @@ pipe_release(struct inode *inode, struct file *file)
pipe->writers--;

if (pipe->readers || pipe->writers) {
- wake_up_interruptible_sync_poll(&pipe->wait, EPOLLIN | EPOLLOUT | EPOLLRDNORM | EPOLLWRNORM | EPOLLERR | EPOLLHUP);
+ wake_up_interruptible_sync_poll(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLHUP);
+ wake_up_interruptible_sync_poll(&pipe->wr_wait, EPOLLOUT | EPOLLWRNORM | EPOLLERR | EPOLLHUP);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}
@@ -789,7 +807,8 @@ struct pipe_inode_info *alloc_pipe_info(void)
GFP_KERNEL_ACCOUNT);

if (pipe->bufs) {
- init_waitqueue_head(&pipe->wait);
+ init_waitqueue_head(&pipe->rd_wait);
+ init_waitqueue_head(&pipe->wr_wait);
pipe->r_counter = pipe->w_counter = 1;
pipe->max_usage = pipe_bufs;
pipe->ring_size = pipe_bufs;
@@ -1007,7 +1026,8 @@ static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)

static void wake_up_partner(struct pipe_inode_info *pipe)
{
- wake_up_interruptible(&pipe->wait);
+ wake_up_interruptible(&pipe->rd_wait);
+ wake_up_interruptible(&pipe->wr_wait);
}

static int fifo_open(struct inode *inode, struct file *filp)
@@ -1118,13 +1138,13 @@ static int fifo_open(struct inode *inode, struct file *filp)

err_rd:
if (!--pipe->readers)
- wake_up_interruptible(&pipe->wait);
+ wake_up_interruptible(&pipe->wr_wait);
ret = -ERESTARTSYS;
goto err;

err_wr:
if (!--pipe->writers)
- wake_up_interruptible(&pipe->wait);
+ wake_up_interruptible(&pipe->rd_wait);
ret = -ERESTARTSYS;
goto err;

@@ -1251,7 +1271,8 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
pipe->max_usage = nr_slots;
pipe->tail = tail;
pipe->head = head;
- wake_up_interruptible_all(&pipe->wait);
+ wake_up_interruptible_all(&pipe->rd_wait);
+ wake_up_interruptible_all(&pipe->wr_wait);
return pipe->max_usage * PAGE_SIZE;

out_revert_acct:
diff --git a/fs/splice.c b/fs/splice.c
index 3009652a41c8..d671936d0aad 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -165,8 +165,8 @@ static const struct pipe_buf_operations user_page_pipe_buf_ops = {
static void wakeup_pipe_readers(struct pipe_inode_info *pipe)
{
smp_mb();
- if (waitqueue_active(&pipe->wait))
- wake_up_interruptible(&pipe->wait);
+ if (waitqueue_active(&pipe->rd_wait))
+ wake_up_interruptible(&pipe->rd_wait);
kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
}

@@ -462,8 +462,8 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
{
smp_mb();
- if (waitqueue_active(&pipe->wait))
- wake_up_interruptible(&pipe->wait);
+ if (waitqueue_active(&pipe->wr_wait))
+ wake_up_interruptible(&pipe->wr_wait);
kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
}

diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index dbcfa6892384..d5765039652a 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -47,7 +47,7 @@ struct pipe_buffer {
**/
struct pipe_inode_info {
struct mutex mutex;
- wait_queue_head_t wait;
+ wait_queue_head_t rd_wait, wr_wait;
unsigned int head;
unsigned int tail;
unsigned int max_usage;
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