From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: jlayton@kernel.org, bfields@fieldses.org, viro@zeniv.linux.org.uk
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: [PATCH v3 2/2] fcntl: fix potential deadlock for &fasync_struct.fa_lock
Date: Wed, 7 Jul 2021 15:44:01 +0800 [thread overview]
Message-ID: <20210707074401.447952-3-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210707074401.447952-1-desmondcheongzx@gmail.com>
There is an existing lock hierarchy of
&dev->event_lock --> &fasync_struct.fa_lock --> &f->f_owner.lock
from the following call chain:
input_inject_event():
spin_lock_irqsave(&dev->event_lock,...);
input_handle_event():
input_pass_values():
input_to_handler():
evdev_events():
evdev_pass_values():
spin_lock(&client->buffer_lock);
__pass_event():
kill_fasync():
kill_fasync_rcu():
read_lock(&fa->fa_lock);
send_sigio():
read_lock_irqsave(&fown->lock,...);
&dev->event_lock is HARDIRQ-safe, so interrupts have to be disabled
while grabbing &fasync_struct.fa_lock, otherwise we invert the lock
hierarchy. However, since kill_fasync which calls kill_fasync_rcu is
an exported symbol, it may not necessarily be called with interrupts
disabled.
As kill_fasync_rcu may be called with interrupts disabled (for
example, in the call chain above), we replace calls to
read_lock/read_unlock on &fasync_struct.fa_lock in kill_fasync_rcu
with read_lock_irqsave/read_unlock_irqrestore.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
fs/fcntl.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index cf9e81dfa615..887db4918a89 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -1004,13 +1004,14 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
{
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;
}
- read_lock(&fa->fa_lock);
+ read_lock_irqsave(&fa->fa_lock, flags);
if (fa->fa_file) {
fown = &fa->fa_file->f_owner;
/* Don't send SIGURG to processes which have not set a
@@ -1019,7 +1020,7 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
if (!(sig == SIGURG && fown->signum == 0))
send_sigio(fown, fa->fa_fd, band);
}
- read_unlock(&fa->fa_lock);
+ read_unlock_irqrestore(&fa->fa_lock, flags);
fa = rcu_dereference(fa->fa_next);
}
}
--
2.25.1
next prev parent reply other threads:[~2021-07-07 7:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 7:43 [PATCH v3 0/2] fcntl: fix potential deadlocks Desmond Cheong Zhi Xi
2021-07-07 7:44 ` [PATCH v3 1/2] fcntl: fix potential deadlocks for &fown_struct.lock Desmond Cheong Zhi Xi
2021-07-07 7:44 ` Desmond Cheong Zhi Xi [this message]
2021-07-07 17:06 ` [PATCH v3 0/2] fcntl: fix potential deadlocks Jeff Layton
2021-07-08 1:52 ` Desmond Cheong Zhi Xi
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