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-rw-r--r--debian/patches-rt/0088-printk-use-atomic64_t-for-devkmsg_user.seq.patch112
1 files changed, 112 insertions, 0 deletions
diff --git a/debian/patches-rt/0088-printk-use-atomic64_t-for-devkmsg_user.seq.patch b/debian/patches-rt/0088-printk-use-atomic64_t-for-devkmsg_user.seq.patch
new file mode 100644
index 000000000..d5c3de71c
--- /dev/null
+++ b/debian/patches-rt/0088-printk-use-atomic64_t-for-devkmsg_user.seq.patch
@@ -0,0 +1,112 @@
+From ccc444abbce9df5f0747db8dd10bd39388d58836 Mon Sep 17 00:00:00 2001
+From: John Ogness <john.ogness@linutronix.de>
+Date: Thu, 10 Dec 2020 15:33:40 +0106
+Subject: [PATCH 088/323] printk: use atomic64_t for devkmsg_user.seq
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+@user->seq is indirectly protected by @logbuf_lock. Once @logbuf_lock
+is removed, @user->seq will be no longer safe from an atomicity point
+of view.
+
+In preparation for the removal of @logbuf_lock, change it to
+atomic64_t to provide this safety.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+---
+ kernel/printk/printk.c | 22 +++++++++++-----------
+ 1 file changed, 11 insertions(+), 11 deletions(-)
+
+diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
+index 4444b3e292d5..a351ed400c04 100644
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -664,7 +664,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
+
+ /* /dev/kmsg - userspace message inject/listen interface */
+ struct devkmsg_user {
+- u64 seq;
++ atomic64_t seq;
+ struct ratelimit_state rs;
+ struct mutex lock;
+ char buf[CONSOLE_EXT_LOG_MAX];
+@@ -766,7 +766,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
+ return ret;
+
+ logbuf_lock_irq();
+- if (!prb_read_valid(prb, user->seq, r)) {
++ if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
+ if (file->f_flags & O_NONBLOCK) {
+ ret = -EAGAIN;
+ logbuf_unlock_irq();
+@@ -775,15 +775,15 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
+
+ logbuf_unlock_irq();
+ ret = wait_event_interruptible(log_wait,
+- prb_read_valid(prb, user->seq, r));
++ prb_read_valid(prb, atomic64_read(&user->seq), r));
+ if (ret)
+ goto out;
+ logbuf_lock_irq();
+ }
+
+- if (r->info->seq != user->seq) {
++ if (r->info->seq != atomic64_read(&user->seq)) {
+ /* our last seen message is gone, return error and reset */
+- user->seq = r->info->seq;
++ atomic64_set(&user->seq, r->info->seq);
+ ret = -EPIPE;
+ logbuf_unlock_irq();
+ goto out;
+@@ -794,7 +794,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
+ &r->text_buf[0], r->info->text_len,
+ &r->info->dev_info);
+
+- user->seq = r->info->seq + 1;
++ atomic64_set(&user->seq, r->info->seq + 1);
+ logbuf_unlock_irq();
+
+ if (len > count) {
+@@ -834,7 +834,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
+ switch (whence) {
+ case SEEK_SET:
+ /* the first record */
+- user->seq = prb_first_valid_seq(prb);
++ atomic64_set(&user->seq, prb_first_valid_seq(prb));
+ break;
+ case SEEK_DATA:
+ /*
+@@ -842,11 +842,11 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
+ * like issued by 'dmesg -c'. Reading /dev/kmsg itself
+ * changes no global state, and does not clear anything.
+ */
+- user->seq = latched_seq_read_nolock(&clear_seq);
++ atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
+ break;
+ case SEEK_END:
+ /* after the last record */
+- user->seq = prb_next_seq(prb);
++ atomic64_set(&user->seq, prb_next_seq(prb));
+ break;
+ default:
+ ret = -EINVAL;
+@@ -869,7 +869,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
+ logbuf_lock_irq();
+ if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
+ /* return error when data has vanished underneath us */
+- if (info.seq != user->seq)
++ if (info.seq != atomic64_read(&user->seq))
+ ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
+ else
+ ret = EPOLLIN|EPOLLRDNORM;
+@@ -908,7 +908,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
+ &user->text_buf[0], sizeof(user->text_buf));
+
+ logbuf_lock_irq();
+- user->seq = prb_first_valid_seq(prb);
++ atomic64_set(&user->seq, prb_first_valid_seq(prb));
+ logbuf_unlock_irq();
+
+ file->private_data = user;
+--
+2.43.0
+