From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A402A19E839; Sat, 23 May 2026 11:08:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779534539; cv=none; b=Ba0zbSN96778rM4WdEXACHeEEuHA7PgQBatRkB4GKfqWKQaykrsSDlj6jjwMUwZmv5RFFwy9xay+sT5yXx2ElMPCjVmIdk0whSZXoHfv5blfUKDcrQEnRl38DqXbBU5v7nqYUcK6BFmzeZHjHalT67r2Z360yh5axKiPJ8fz1m8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779534539; c=relaxed/simple; bh=/rATDfuzA3+uloN3KuIMCipks2T2AhZNulKR+fu/INU=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=brqpLlq3iYBV9w0cf9Ft7VpgBFm+qb2XjNyynRpRvfenHUJK2g9I7C5HCc6nqEp316uTRSO7XVJ2V3yiLKC1w24VnO0vug2QbFYvSH/7YtIL/2fa/hvEJy68wQP0UV7ROlu/JccwBfIMqSUmiYU2H2tF5GM39eM9qqsokWyFM00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GUAoMIFX; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GUAoMIFX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64EC61F000E9; Sat, 23 May 2026 11:08:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779534537; bh=c1nhiYP+DkWIoRSGmfrDDu8S2cz6zN1sSX/qW4ZjiIY=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=GUAoMIFXOhY3PB1FrKGcnaXf8UR503rTPPYe3+R3i3JoCjSWhOaua36pmGeoov/Y8 JeyGYxnct96bGrW3x+2haypldCgudrri/Ey5PrpJiAYbja+NN4aw4J/2edB/hcWMJa y+dPXjTLIoMtESYvbN3tLhp3wKKgOMvVsyo4k1woppXE1xyKs5aWgEwCLUI6S+SLw/ RBAw93Mn6H4UA2bBdFsZlOrwMeBrjrKuX4cxDhn77q1/V8dewh8dJ5bhHEnQVYQvDv ip6KWAOfSLtGbCdS4koMFNuuj1vsPnZsQihf0HWT07z6XRiqFqX+I8YINq7BZsRgyh PgFAo+4GliLrw== Message-ID: Subject: Re: [PATCH] fs/fcntl: fix SOFTIRQ-unsafe lock order in send_sigio() From: Jeff Layton To: w15303746062@163.com, chuck.lever@oracle.com, viro@zeniv.linux.org.uk, brauner@kernel.org Cc: alex.aring@gmail.com, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Mingyu Wang <25181214217@stu.xidian.edu.cn> Date: Sat, 23 May 2026 07:08:54 -0400 In-Reply-To: <20260523080255.585201-1-w15303746062@163.com> References: <20260523080255.585201-1-w15303746062@163.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Sat, 2026-05-23 at 16:02 +0800, w15303746062@163.com wrote: > From: Mingyu Wang <25181214217@stu.xidian.edu.cn> >=20 > A SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in > send_sigio() when a process group receives a SIGIO. >=20 > When FASYNC is configured for a process group (PIDTYPE_PGID), > send_sigio() uses read_lock(&tasklist_lock) to traverse the task > list. However, send_sigio() is often called from softirq context > (e.g., input_inject_event -> kill_fasync), where it already holds > SOFTIRQ-safe locks like &dev->event_lock and &f_owner->lock. >=20 > The deadlock is caused by the rwlock writer fairness mechanism: > 1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait(). > 2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in > fork() or exit() and spins, which blocks all new readers. > 3. CPU 0 is interrupted by a softirq (e.g., keyboard input event). > 4. The softirq calls send_sigio() and attempts to acquire > read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting. >=20 > Since PID hashing and do_each_pid_task() traversals are already > RCU-protected, the read_lock on tasklist_lock is no longer strictly > required for safe traversal. Fix this by replacing tasklist_lock with > rcu_read_lock(), aligning the process group signaling path with the > single-PID path. >=20 > Lockdep splat: > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D > WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected > [...] > Chain exists of: > &dev->event_lock --> &f_owner->lock --> tasklist_lock >=20 > Possible interrupt unsafe locking scenario: > CPU0 CPU1 > ---- ---- > lock(tasklist_lock); > local_irq_disable(); > lock(&dev->event_lock); > lock(&f_owner->lock); > > lock(&dev->event_lock); >=20 > *** DEADLOCK *** >=20 > Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> > --- > fs/fcntl.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/fs/fcntl.c b/fs/fcntl.c > index beab8080badf..a6c764ede282 100644 > --- a/fs/fcntl.c > +++ b/fs/fcntl.c > @@ -929,11 +929,11 @@ void send_sigio(struct fown_struct *fown, int fd, i= nt band) > send_sigio_to_task(p, fown, fd, band, type); > rcu_read_unlock(); > } else { > - read_lock(&tasklist_lock); > + rcu_read_lock(); > do_each_pid_task(pid, type, p) { > send_sigio_to_task(p, fown, fd, band, type); > } while_each_pid_task(pid, type, p); > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > } > out_unlock_fown: > read_unlock_irqrestore(&fown->lock, flags); This looks good to me. Sashiko seems to think that send_sigurg has the same problem though. Care to look into fixing that one too? https://sashiko.dev/#/patchset/20260523080255.585201-1-w15303746062%40163.c= om You can add: Reviewed-by: Jeff Layton