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@antgroup.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@antgroup.com Link: https://patch.msgid.link/20250319135523.97050-4-tiwei.btw@antgroup.com Signed-off-by: Johannes Berg johannes.berg@intel.com Signed-off-by: Sasha Levin sashal@kernel.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/commi...

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 = &current_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);