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Message-ID: <ffa0b6af-523d-4e3e-9952-92f5b04b82b3@antgroup.com>
Date: Tue, 08 Apr 2025 12:29:53 +0800
From: "Tiwei Bie" <tiwei.btw@...group.com>
To: Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Cc: Johannes Berg <johannes.berg@...el.com>, richard@....at,
anton.ivanov@...bridgegreys.com, johannes@...solutions.net,
linux-um@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 6.14 25/31] um: Switch to the pthread-based helper
in sigio workaround
On 2025/4/8 02:10, Sasha Levin wrote:
> From: Tiwei Bie <tiwei.btw@...group.com>
>
> [ Upstream commit d295beeed2552a987796d627ba7d0985b1e2d72f ]
>
> The write_sigio thread and UML kernel thread share the same errno,
> which can lead to conflicts when both call syscalls concurrently.
> Switch to the pthread-based helper to address this issue.
>
> Signed-off-by: Tiwei Bie <tiwei.btw@...group.com>
> Link: https://patch.msgid.link/20250319135523.97050-4-tiwei.btw@antgroup.com
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
> arch/um/os-Linux/sigio.c | 44 +++++++++++++++++-----------------------
> 1 file changed, 19 insertions(+), 25 deletions(-)
This patch depends on the helpers introduced by the below patch:
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4f087eafdcef24b7160b097ddb9704084767b77a
So it can't be backported to the stable branch alone. Please drop
it. It is more of a preparation for the new features to be added
in the future. If it turns out later that it is also necessary for
the stable branch, I will submit a separate patchset specifically
targeting it.
Regards,
Tiwei
>
> diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
> index 9aac8def4d635..61b348a2ea974 100644
> --- a/arch/um/os-Linux/sigio.c
> +++ b/arch/um/os-Linux/sigio.c
> @@ -21,8 +21,7 @@
> * Protected by sigio_lock(), also used by sigio_cleanup, which is an
> * exitcall.
> */
> -static int write_sigio_pid = -1;
> -static unsigned long write_sigio_stack;
> +static struct os_helper_thread *write_sigio_td;
>
> /*
> * These arrays are initialized before the sigio thread is started, and
> @@ -48,15 +47,15 @@ static struct pollfds current_poll;
> static struct pollfds next_poll;
> static struct pollfds all_sigio_fds;
>
> -static int write_sigio_thread(void *unused)
> +static void *write_sigio_thread(void *unused)
> {
> struct pollfds *fds, tmp;
> struct pollfd *p;
> int i, n, respond_fd;
> char c;
>
> - os_set_pdeathsig();
> - os_fix_helper_signals();
> + os_fix_helper_thread_signals();
> +
> fds = ¤t_poll;
> while (1) {
> n = poll(fds->poll, fds->used, -1);
> @@ -98,7 +97,7 @@ static int write_sigio_thread(void *unused)
> }
> }
>
> - return 0;
> + return NULL;
> }
>
> static int need_poll(struct pollfds *polls, int n)
> @@ -152,11 +151,10 @@ static void update_thread(void)
> return;
> fail:
> /* Critical section start */
> - if (write_sigio_pid != -1) {
> - os_kill_process(write_sigio_pid, 1);
> - free_stack(write_sigio_stack, 0);
> + if (write_sigio_td) {
> + os_kill_helper_thread(write_sigio_td);
> + write_sigio_td = NULL;
> }
> - write_sigio_pid = -1;
> close(sigio_private[0]);
> close(sigio_private[1]);
> close(write_sigio_fds[0]);
> @@ -220,7 +218,7 @@ int __ignore_sigio_fd(int fd)
> * sigio_cleanup has already run, then update_thread will hang
> * or fail because the thread is no longer running.
> */
> - if (write_sigio_pid == -1)
> + if (!write_sigio_td)
> return -EIO;
>
> for (i = 0; i < current_poll.used; i++) {
> @@ -279,14 +277,14 @@ static void write_sigio_workaround(void)
> int err;
> int l_write_sigio_fds[2];
> int l_sigio_private[2];
> - int l_write_sigio_pid;
> + struct os_helper_thread *l_write_sigio_td;
>
> /* We call this *tons* of times - and most ones we must just fail. */
> sigio_lock();
> - l_write_sigio_pid = write_sigio_pid;
> + l_write_sigio_td = write_sigio_td;
> sigio_unlock();
>
> - if (l_write_sigio_pid != -1)
> + if (l_write_sigio_td)
> return;
>
> err = os_pipe(l_write_sigio_fds, 1, 1);
> @@ -312,7 +310,7 @@ static void write_sigio_workaround(void)
> * Did we race? Don't try to optimize this, please, it's not so likely
> * to happen, and no more than once at the boot.
> */
> - if (write_sigio_pid != -1)
> + if (write_sigio_td)
> goto out_free;
>
> current_poll = ((struct pollfds) { .poll = p,
> @@ -325,18 +323,15 @@ static void write_sigio_workaround(void)
> memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
> memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
>
> - write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
> - CLONE_FILES | CLONE_VM,
> - &write_sigio_stack);
> -
> - if (write_sigio_pid < 0)
> + err = os_run_helper_thread(&write_sigio_td, write_sigio_thread, NULL);
> + if (err < 0)
> goto out_clear;
>
> sigio_unlock();
> return;
>
> out_clear:
> - write_sigio_pid = -1;
> + write_sigio_td = NULL;
> write_sigio_fds[0] = -1;
> write_sigio_fds[1] = -1;
> sigio_private[0] = -1;
> @@ -394,12 +389,11 @@ void maybe_sigio_broken(int fd)
>
> static void sigio_cleanup(void)
> {
> - if (write_sigio_pid == -1)
> + if (!write_sigio_td)
> return;
>
> - os_kill_process(write_sigio_pid, 1);
> - free_stack(write_sigio_stack, 0);
> - write_sigio_pid = -1;
> + os_kill_helper_thread(write_sigio_td);
> + write_sigio_td = NULL;
> }
>
> __uml_exitcall(sigio_cleanup);
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