* [PATCH AUTOSEL 6.14 25/31] um: Switch to the pthread-based helper in sigio workaround
[not found] <20250407181054.3177479-1-sashal@kernel.org>
2025-04-07 18:10 ` [PATCH AUTOSEL 6.14 23/31] um: work around sched_yield not yielding in time-travel mode Sasha Levin
@ 2025-04-07 18:10 ` Sasha Levin
2025-04-08 4:29 ` Tiwei Bie
2025-04-07 18:10 ` [PATCH AUTOSEL 6.14 26/31] um: Rewrite the sigio workaround based on epoll and tgkill Sasha Levin
2 siblings, 1 reply; 5+ messages in thread
From: Sasha Levin @ 2025-04-07 18:10 UTC (permalink / raw)
To: linux-kernel, stable
Cc: Tiwei Bie, Johannes Berg, Sasha Levin, richard, anton.ivanov,
johannes, linux-um
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(-)
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);
--
2.39.5
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH AUTOSEL 6.14 26/31] um: Rewrite the sigio workaround based on epoll and tgkill
[not found] <20250407181054.3177479-1-sashal@kernel.org>
2025-04-07 18:10 ` [PATCH AUTOSEL 6.14 23/31] um: work around sched_yield not yielding in time-travel mode Sasha Levin
2025-04-07 18:10 ` [PATCH AUTOSEL 6.14 25/31] um: Switch to the pthread-based helper in sigio workaround Sasha Levin
@ 2025-04-07 18:10 ` Sasha Levin
2025-04-08 4:36 ` Tiwei Bie
2 siblings, 1 reply; 5+ messages in thread
From: Sasha Levin @ 2025-04-07 18:10 UTC (permalink / raw)
To: linux-kernel, stable
Cc: Tiwei Bie, Johannes Berg, Sasha Levin, richard, anton.ivanov,
johannes, benjamin.berg, linux-um
From: Tiwei Bie <tiwei.btw@antgroup.com>
[ Upstream commit 33c9da5dfb18c2ff5a88d01aca2cf253cd0ac3bc ]
The existing sigio workaround implementation removes FDs from the
poll when events are triggered, requiring users to re-add them via
add_sigio_fd() after processing. This introduces a potential race
condition between FD removal in write_sigio_thread() and next_poll
update in __add_sigio_fd(), and is inefficient due to frequent FD
removal and re-addition. Rewrite the implementation based on epoll
and tgkill for improved efficiency and reliability.
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250315161910.4082396-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/um/drivers/random.c | 2 +-
arch/um/drivers/rtc_user.c | 2 +-
arch/um/include/shared/os.h | 2 +-
arch/um/include/shared/sigio.h | 1 -
arch/um/kernel/sigio.c | 26 ---
arch/um/os-Linux/sigio.c | 330 +++++----------------------------
6 files changed, 47 insertions(+), 316 deletions(-)
diff --git a/arch/um/drivers/random.c b/arch/um/drivers/random.c
index da985e0dc69a5..ca08c91f47a37 100644
--- a/arch/um/drivers/random.c
+++ b/arch/um/drivers/random.c
@@ -79,7 +79,7 @@ static int __init rng_init (void)
if (err < 0)
goto err_out_cleanup_hw;
- sigio_broken(random_fd);
+ sigio_broken();
hwrng.name = RNG_MODULE_NAME;
hwrng.read = rng_dev_read;
diff --git a/arch/um/drivers/rtc_user.c b/arch/um/drivers/rtc_user.c
index 7c3cec4c68cff..51e79f3148cd4 100644
--- a/arch/um/drivers/rtc_user.c
+++ b/arch/um/drivers/rtc_user.c
@@ -39,7 +39,7 @@ int uml_rtc_start(bool timetravel)
}
/* apparently timerfd won't send SIGIO, use workaround */
- sigio_broken(uml_rtc_irq_fds[0]);
+ sigio_broken();
err = add_sigio_fd(uml_rtc_irq_fds[0]);
if (err < 0) {
close(uml_rtc_irq_fds[0]);
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 5babad8c5f75e..92868f398457a 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -310,7 +310,7 @@ extern void um_irqs_resume(void);
extern int add_sigio_fd(int fd);
extern int ignore_sigio_fd(int fd);
extern void maybe_sigio_broken(int fd);
-extern void sigio_broken(int fd);
+extern void sigio_broken(void);
/*
* unlocked versions for IRQ controller code.
*
diff --git a/arch/um/include/shared/sigio.h b/arch/um/include/shared/sigio.h
index e60c8b2278449..c6c2edce1f6d2 100644
--- a/arch/um/include/shared/sigio.h
+++ b/arch/um/include/shared/sigio.h
@@ -6,7 +6,6 @@
#ifndef __SIGIO_H__
#define __SIGIO_H__
-extern int write_sigio_irq(int fd);
extern void sigio_lock(void);
extern void sigio_unlock(void);
diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
index 5085a50c3b8c8..4fc04742048ab 100644
--- a/arch/um/kernel/sigio.c
+++ b/arch/um/kernel/sigio.c
@@ -8,32 +8,6 @@
#include <os.h>
#include <sigio.h>
-/* Protected by sigio_lock() called from write_sigio_workaround */
-static int sigio_irq_fd = -1;
-
-static irqreturn_t sigio_interrupt(int irq, void *data)
-{
- char c;
-
- os_read_file(sigio_irq_fd, &c, sizeof(c));
- return IRQ_HANDLED;
-}
-
-int write_sigio_irq(int fd)
-{
- int err;
-
- err = um_request_irq(SIGIO_WRITE_IRQ, fd, IRQ_READ, sigio_interrupt,
- 0, "write sigio", NULL);
- if (err < 0) {
- printk(KERN_ERR "write_sigio_irq : um_request_irq failed, "
- "err = %d\n", err);
- return -1;
- }
- sigio_irq_fd = fd;
- return 0;
-}
-
/* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
static DEFINE_MUTEX(sigio_mutex);
diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
index 61b348a2ea974..a05a6ecee7561 100644
--- a/arch/um/os-Linux/sigio.c
+++ b/arch/um/os-Linux/sigio.c
@@ -11,6 +11,7 @@
#include <sched.h>
#include <signal.h>
#include <string.h>
+#include <sys/epoll.h>
#include <kern_util.h>
#include <init.h>
#include <os.h>
@@ -23,180 +24,49 @@
*/
static struct os_helper_thread *write_sigio_td;
-/*
- * These arrays are initialized before the sigio thread is started, and
- * the descriptors closed after it is killed. So, it can't see them change.
- * On the UML side, they are changed under the sigio_lock.
- */
-#define SIGIO_FDS_INIT {-1, -1}
-
-static int write_sigio_fds[2] = SIGIO_FDS_INIT;
-static int sigio_private[2] = SIGIO_FDS_INIT;
+static int epollfd = -1;
-struct pollfds {
- struct pollfd *poll;
- int size;
- int used;
-};
+#define MAX_EPOLL_EVENTS 64
-/*
- * Protected by sigio_lock(). Used by the sigio thread, but the UML thread
- * synchronizes with it.
- */
-static struct pollfds current_poll;
-static struct pollfds next_poll;
-static struct pollfds all_sigio_fds;
+static struct epoll_event epoll_events[MAX_EPOLL_EVENTS];
static void *write_sigio_thread(void *unused)
{
- struct pollfds *fds, tmp;
- struct pollfd *p;
- int i, n, respond_fd;
- char c;
+ int pid = getpid();
+ int r;
os_fix_helper_thread_signals();
- fds = ¤t_poll;
while (1) {
- n = poll(fds->poll, fds->used, -1);
- if (n < 0) {
+ r = epoll_wait(epollfd, epoll_events, MAX_EPOLL_EVENTS, -1);
+ if (r < 0) {
if (errno == EINTR)
continue;
- printk(UM_KERN_ERR "write_sigio_thread : poll returned "
- "%d, errno = %d\n", n, errno);
+ printk(UM_KERN_ERR "%s: epoll_wait failed, errno = %d\n",
+ __func__, errno);
}
- for (i = 0; i < fds->used; i++) {
- p = &fds->poll[i];
- if (p->revents == 0)
- continue;
- if (p->fd == sigio_private[1]) {
- CATCH_EINTR(n = read(sigio_private[1], &c,
- sizeof(c)));
- if (n != sizeof(c))
- printk(UM_KERN_ERR
- "write_sigio_thread : "
- "read on socket failed, "
- "err = %d\n", errno);
- tmp = current_poll;
- current_poll = next_poll;
- next_poll = tmp;
- respond_fd = sigio_private[1];
- }
- else {
- respond_fd = write_sigio_fds[1];
- fds->used--;
- memmove(&fds->poll[i], &fds->poll[i + 1],
- (fds->used - i) * sizeof(*fds->poll));
- }
-
- CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
- if (n != sizeof(c))
- printk(UM_KERN_ERR "write_sigio_thread : "
- "write on socket failed, err = %d\n",
- errno);
- }
- }
-
- return NULL;
-}
-
-static int need_poll(struct pollfds *polls, int n)
-{
- struct pollfd *new;
-
- if (n <= polls->size)
- return 0;
-
- new = uml_kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
- if (new == NULL) {
- printk(UM_KERN_ERR "need_poll : failed to allocate new "
- "pollfds\n");
- return -ENOMEM;
- }
-
- memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
- kfree(polls->poll);
-
- polls->poll = new;
- polls->size = n;
- return 0;
-}
-
-/*
- * Must be called with sigio_lock held, because it's needed by the marked
- * critical section.
- */
-static void update_thread(void)
-{
- unsigned long flags;
- int n;
- char c;
-
- flags = um_set_signals_trace(0);
- CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
- if (n != sizeof(c)) {
- printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
- errno);
- goto fail;
- }
- CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
- if (n != sizeof(c)) {
- printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
- errno);
- goto fail;
+ CATCH_EINTR(r = tgkill(pid, pid, SIGIO));
+ if (r < 0)
+ printk(UM_KERN_ERR "%s: tgkill failed, errno = %d\n",
+ __func__, errno);
}
- um_set_signals_trace(flags);
- return;
- fail:
- /* Critical section start */
- if (write_sigio_td) {
- os_kill_helper_thread(write_sigio_td);
- write_sigio_td = NULL;
- }
- close(sigio_private[0]);
- close(sigio_private[1]);
- close(write_sigio_fds[0]);
- close(write_sigio_fds[1]);
- /* Critical section end */
- um_set_signals_trace(flags);
+ return NULL;
}
int __add_sigio_fd(int fd)
{
- struct pollfd *p;
- int err, i, n;
-
- for (i = 0; i < all_sigio_fds.used; i++) {
- if (all_sigio_fds.poll[i].fd == fd)
- break;
- }
- if (i == all_sigio_fds.used)
- return -ENOSPC;
-
- p = &all_sigio_fds.poll[i];
-
- for (i = 0; i < current_poll.used; i++) {
- if (current_poll.poll[i].fd == fd)
- return 0;
- }
-
- n = current_poll.used;
- err = need_poll(&next_poll, n + 1);
- if (err)
- return err;
-
- memcpy(next_poll.poll, current_poll.poll,
- current_poll.used * sizeof(struct pollfd));
- next_poll.poll[n] = *p;
- next_poll.used = n + 1;
- update_thread();
-
- return 0;
+ struct epoll_event event = {
+ .data.fd = fd,
+ .events = EPOLLIN | EPOLLET,
+ };
+ int r;
+
+ CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event));
+ return r < 0 ? -errno : 0;
}
-
int add_sigio_fd(int fd)
{
int err;
@@ -210,38 +80,11 @@ int add_sigio_fd(int fd)
int __ignore_sigio_fd(int fd)
{
- struct pollfd *p;
- int err, i, n = 0;
-
- /*
- * This is called from exitcalls elsewhere in UML - if
- * sigio_cleanup has already run, then update_thread will hang
- * or fail because the thread is no longer running.
- */
- if (!write_sigio_td)
- return -EIO;
-
- for (i = 0; i < current_poll.used; i++) {
- if (current_poll.poll[i].fd == fd)
- break;
- }
- if (i == current_poll.used)
- return -ENOENT;
-
- err = need_poll(&next_poll, current_poll.used - 1);
- if (err)
- return err;
+ struct epoll_event event;
+ int r;
- for (i = 0; i < current_poll.used; i++) {
- p = ¤t_poll.poll[i];
- if (p->fd != fd)
- next_poll.poll[n++] = *p;
- }
- next_poll.used = current_poll.used - 1;
-
- update_thread();
-
- return 0;
+ CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &event));
+ return r < 0 ? -errno : 0;
}
int ignore_sigio_fd(int fd)
@@ -255,122 +98,37 @@ int ignore_sigio_fd(int fd)
return err;
}
-static struct pollfd *setup_initial_poll(int fd)
-{
- struct pollfd *p;
-
- p = uml_kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
- if (p == NULL) {
- printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
- "poll\n");
- return NULL;
- }
- *p = ((struct pollfd) { .fd = fd,
- .events = POLLIN,
- .revents = 0 });
- return p;
-}
-
static void write_sigio_workaround(void)
{
- struct pollfd *p;
int err;
- int l_write_sigio_fds[2];
- int l_sigio_private[2];
- 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_td = write_sigio_td;
- sigio_unlock();
-
- if (l_write_sigio_td)
- return;
-
- err = os_pipe(l_write_sigio_fds, 1, 1);
- if (err < 0) {
- printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
- "err = %d\n", -err);
- return;
- }
- err = os_pipe(l_sigio_private, 1, 1);
- if (err < 0) {
- printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
- "err = %d\n", -err);
- goto out_close1;
- }
-
- p = setup_initial_poll(l_sigio_private[1]);
- if (!p)
- goto out_close2;
sigio_lock();
-
- /*
- * 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_td)
- goto out_free;
-
- current_poll = ((struct pollfds) { .poll = p,
- .used = 1,
- .size = 1 });
-
- if (write_sigio_irq(l_write_sigio_fds[0]))
- goto out_clear_poll;
+ goto out;
- memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
- memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
+ epollfd = epoll_create(MAX_EPOLL_EVENTS);
+ if (epollfd < 0) {
+ printk(UM_KERN_ERR "%s: epoll_create failed, errno = %d\n",
+ __func__, errno);
+ goto out;
+ }
err = os_run_helper_thread(&write_sigio_td, write_sigio_thread, NULL);
- if (err < 0)
- goto out_clear;
-
- sigio_unlock();
- return;
+ if (err < 0) {
+ printk(UM_KERN_ERR "%s: os_run_helper_thread failed, errno = %d\n",
+ __func__, -err);
+ close(epollfd);
+ epollfd = -1;
+ goto out;
+ }
-out_clear:
- write_sigio_td = NULL;
- write_sigio_fds[0] = -1;
- write_sigio_fds[1] = -1;
- sigio_private[0] = -1;
- sigio_private[1] = -1;
-out_clear_poll:
- current_poll = ((struct pollfds) { .poll = NULL,
- .size = 0,
- .used = 0 });
-out_free:
+out:
sigio_unlock();
- kfree(p);
-out_close2:
- close(l_sigio_private[0]);
- close(l_sigio_private[1]);
-out_close1:
- close(l_write_sigio_fds[0]);
- close(l_write_sigio_fds[1]);
}
-void sigio_broken(int fd)
+void sigio_broken(void)
{
- int err;
-
write_sigio_workaround();
-
- sigio_lock();
- err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
- if (err) {
- printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
- "for descriptor %d\n", fd);
- goto out;
- }
-
- all_sigio_fds.poll[all_sigio_fds.used++] =
- ((struct pollfd) { .fd = fd,
- .events = POLLIN,
- .revents = 0 });
-out:
- sigio_unlock();
}
/* Changed during early boot */
@@ -384,7 +142,7 @@ void maybe_sigio_broken(int fd)
if (pty_output_sigio)
return;
- sigio_broken(fd);
+ sigio_broken();
}
static void sigio_cleanup(void)
--
2.39.5
^ permalink raw reply related [flat|nested] 5+ messages in thread