On Wed, Aug 27, 2025 at 04:39:00PM +0300, Lauri Vasama wrote:
> For a user mode library to avoid generating SIGPIPE signals (e.g.
> because this behaviour is not portable across operating systems) is
> cumbersome. It is generally bad form to change the process-wide signal
> mask in a library, so a local solution is needed instead.
>
> For I/O performed directly using system calls (synchronous or readiness
> based asynchronous) this currently involves applying a thread-specific
> signal mask before the operation and reverting it afterwards. This can be
> avoided when it is known that the file descriptor refers to neither a
> pipe nor a socket, but a conservative implementation must always apply
> the mask. This incurs the cost of two additional system calls. In the
> case of sockets, the existing MSG_NOSIGNAL flag can be used with send.
>
> For asynchronous I/O performed using io_uring, currently the only option
> (apart from MSG_NOSIGNAL for sockets), is to mask SIGPIPE entirely in the
> call to io_uring_enter. Thankfully io_uring_enter takes a signal mask, so
> only a single syscall is needed. However, copying the signal mask on
> every call incurs a non-zero performance penalty. Furthermore, this mask
> applies to all completions, meaning that if the non-signaling behaviour
> is desired only for some subset of operations, the desired signals must
> be raised manually from user-mode depending on the completed operation.
>
> Add RWF_NOSIGNAL flag for pwritev2. This flag prevents the SIGPIPE signal
> from being raised when writing on disconnected pipes or sockets. The flag
> is handled directly by the pipe filesystem and converted to the existing
> MSG_NOSIGNAL flag for sockets.
>
> Signed-off-by: Lauri Vasama <git@xxxxxxxxxx>
> ---
So this makes sense to me.
I'll wait for @Jens to chime in, too, before I apply it.
> fs/pipe.c | 6 ++++--
> include/linux/fs.h | 1 +
> include/uapi/linux/fs.h | 5 ++++-
> net/socket.c | 3 +++
> 4 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 731622d0738d..42fead1efe52 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -458,7 +458,8 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
> mutex_lock(&pipe->mutex);
>
> if (!pipe->readers) {
> - send_sig(SIGPIPE, current, 0);
> + if ((iocb->ki_flags & IOCB_NOSIGNAL) == 0)
> + send_sig(SIGPIPE, current, 0);
> ret = -EPIPE;
> goto out;
> }
> @@ -498,7 +499,8 @@ anon_pipe_write(struct kiocb *iocb, struct iov_iter *from)
>
> for (;;) {
> if (!pipe->readers) {
> - send_sig(SIGPIPE, current, 0);
> + if ((iocb->ki_flags & IOCB_NOSIGNAL) == 0)
> + send_sig(SIGPIPE, current, 0);
> if (!ret)
> ret = -EPIPE;
> break;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ab4f96d705..e440c5ae5d99 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -356,6 +356,7 @@ struct readahead_control;
> #define IOCB_APPEND (__force int) RWF_APPEND
> #define IOCB_ATOMIC (__force int) RWF_ATOMIC
> #define IOCB_DONTCACHE (__force int) RWF_DONTCACHE
> +#define IOCB_NOSIGNAL (__force int) RWF_NOSIGNAL
>
> /* non-RWF related bits - start at 16 */
> #define IOCB_EVENTFD (1 << 16)
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 0bd678a4a10e..beb4c2d1e41c 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -430,10 +430,13 @@ typedef int __bitwise __kernel_rwf_t;
> /* buffered IO that drops the cache after reading or writing data */
> #define RWF_DONTCACHE ((__force __kernel_rwf_t)0x00000080)
>
> +/* prevent pipe and socket writes from raising SIGPIPE */
> +#define RWF_NOSIGNAL ((__force __kernel_rwf_t)0x00000100)
> +
> /* mask of flags supported by the kernel */
> #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC |\
> - RWF_DONTCACHE)
> + RWF_DONTCACHE | RWF_NOSIGNAL)
>
> #define PROCFS_IOCTL_MAGIC 'f'
>
> diff --git a/net/socket.c b/net/socket.c
> index 682969deaed3..bac335ecee4c 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1176,6 +1176,9 @@ static ssize_t sock_write_iter(struct kiocb *iocb, struct iov_iter *from)
> if (sock->type == SOCK_SEQPACKET)
> msg.msg_flags |= MSG_EOR;
>
> + if (iocb->ki_flags & IOCB_NOSIGNAL)
> + msg.msg_flags |= MSG_NOSIGNAL;
> +
> res = __sock_sendmsg(sock, &msg);
> *from = msg.msg_iter;
> return res;
>
> base-commit: fab1beda7597fac1cecc01707d55eadb6bbe773c
> --
> 2.43.0
>
