4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
[ Upstream commit 7a107c0f55a3b4c6f84a4323df5610360bde1684 ]
I observed the following deadlock between them:
[task 1] [task 2] [task 3]
kill_fasync() mm_update_next_owner() copy_process()
spin_lock_irqsave(&fa->fa_lock) read_lock(&tasklist_lock) write_lock_irq(&tasklist_lock)
send_sigio() <IRQ> ...
read_lock(&fown->lock) kill_fasync() ...
read_lock(&tasklist_lock) spin_lock_irqsave(&fa->fa_lock) ...
Task 1 can't acquire read locked tasklist_lock, since there is
already task 3 expressed its wish to take the lock exclusive.
Task 2 holds the read locked lock, but it can't take the spin lock.
Also, there is possible another deadlock (which I haven't observed):
[task 1] [task 2]
f_getown() kill_fasync()
read_lock(&f_own->lock) spin_lock_irqsave(&fa->fa_lock,)
<IRQ> send_sigio() write_lock_irq(&f_own->lock)
kill_fasync() read_lock(&fown->lock)
spin_lock_irqsave(&fa->fa_lock,)
Actually, we do not need exclusive fa->fa_lock in kill_fasync_rcu(),
as it guarantees fa->fa_file->f_owner integrity only. It may seem,
that it used to give a task a small possibility to receive two sequential
signals, if there are two parallel kill_fasync() callers, and task
handles the first signal fastly, but the behaviour won't become
different, since there is exclusive sighand lock in do_send_sig_info().
The patch converts fa_lock into rwlock_t, and this fixes two above
deadlocks, as rwlock is allowed to be taken from interrupt handler
by qrwlock design.
Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/fcntl.c | 15 +++++++--------
include/linux/fs.h | 2 +-
2 files changed, 8 insertions(+), 9 deletions(-)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -871,9 +871,9 @@ int fasync_remove_entry(struct file *fil
if (fa->fa_file != filp)
continue;
- spin_lock_irq(&fa->fa_lock);
+ write_lock_irq(&fa->fa_lock);
fa->fa_file = NULL;
- spin_unlock_irq(&fa->fa_lock);
+ write_unlock_irq(&fa->fa_lock);
*fp = fa->fa_next;
call_rcu(&fa->fa_rcu, fasync_free_rcu);
@@ -918,13 +918,13 @@ struct fasync_struct *fasync_insert_entr
if (fa->fa_file != filp)
continue;
- spin_lock_irq(&fa->fa_lock);
+ write_lock_irq(&fa->fa_lock);
fa->fa_fd = fd;
- spin_unlock_irq(&fa->fa_lock);
+ write_unlock_irq(&fa->fa_lock);
goto out;
}
- spin_lock_init(&new->fa_lock);
+ rwlock_init(&new->fa_lock);
new->magic = FASYNC_MAGIC;
new->fa_file = filp;
new->fa_fd = fd;
@@ -987,14 +987,13 @@ static void kill_fasync_rcu(struct fasyn
{
while (fa) {
struct fown_struct *fown;
- unsigned long flags;
if (fa->magic != FASYNC_MAGIC) {
printk(KERN_ERR "kill_fasync: bad magic number in "
"fasync_struct!\n");
return;
}
- spin_lock_irqsave(&fa->fa_lock, flags);
+ read_lock(&fa->fa_lock);
if (fa->fa_file) {
fown = &fa->fa_file->f_owner;
/* Don't send SIGURG to processes which have not set a
@@ -1003,7 +1002,7 @@ static void kill_fasync_rcu(struct fasyn
if (!(sig == SIGURG && fown->signum == 0))
send_sigio(fown, fa->fa_fd, band);
}
- spin_unlock_irqrestore(&fa->fa_lock, flags);
+ read_unlock(&fa->fa_lock);
fa = rcu_dereference(fa->fa_next);
}
}
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1250,7 +1250,7 @@ static inline int locks_lock_file_wait(s
}
struct fasync_struct {
- spinlock_t fa_lock;
+ rwlock_t fa_lock;
int magic;
int fa_fd;
struct fasync_struct *fa_next; /* singly linked list */
