From: Byungchul Park <byungchul.park@lge.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org,
torvalds@linux-foundation.org, mingo@redhat.com,
linux-kernel@vger.kernel.org, peterz@infradead.org,
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daniel.vetter@ffwll.ch, chris@chris-wilson.co.uk,
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bfields@fieldses.org, gregkh@linuxfoundation.org,
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jglisse@redhat.com, dennis@kernel.org, cl@linux.com,
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hch@infradead.org, djwong@kernel.org,
dri-devel@lists.freedesktop.org, airlied@linux.ie,
rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com,
hamohammed.sa@gmail.com
Subject: Re: Report in unix_stream_read_generic()
Date: Fri, 18 Feb 2022 08:50:42 +0900 [thread overview]
Message-ID: <20220217235042.GA20620@X58A-UD3R> (raw)
In-Reply-To: <Ygx+pRo1+b1RBLJg@casper.infradead.org>
On Wed, Feb 16, 2022 at 04:33:41AM +0000, Matthew Wilcox wrote:
> On Wed, Feb 16, 2022 at 01:17:03PM +0900, Byungchul Park wrote:
> > [ 7.013330] ===================================================
> > [ 7.013331] DEPT: Circular dependency has been detected.
> > [ 7.013332] 5.17.0-rc1-00014-gcf3441bb2012 #2 Tainted: G W
> > [ 7.013333] ---------------------------------------------------
> > [ 7.013334] summary
> > [ 7.013334] ---------------------------------------------------
> > [ 7.013335] *** DEADLOCK ***
> > [ 7.013335]
> > [ 7.013335] context A
> > [ 7.013336] [S] (unknown)(&(&ei->socket.wq.wait)->dmap:0)
> > [ 7.013337] [W] __mutex_lock_common(&u->iolock:0)
> > [ 7.013338] [E] event(&(&ei->socket.wq.wait)->dmap:0)
> > [ 7.013340]
> > [ 7.013340] context B
> > [ 7.013341] [S] __raw_spin_lock(&u->lock:0)
> > [ 7.013342] [W] wait(&(&ei->socket.wq.wait)->dmap:0)
> > [ 7.013343] [E] spin_unlock(&u->lock:0)
>
> This seems unlikely to be real. We're surely not actually waiting
> while holding a spinlock; existing debug checks would catch it.
>
> > [ 7.013407] ---------------------------------------------------
> > [ 7.013407] context B's detail
> > [ 7.013408] ---------------------------------------------------
> > [ 7.013408] context B
> > [ 7.013409] [S] __raw_spin_lock(&u->lock:0)
> > [ 7.013410] [W] wait(&(&ei->socket.wq.wait)->dmap:0)
> > [ 7.013411] [E] spin_unlock(&u->lock:0)
> > [ 7.013412]
> > [ 7.013412] [S] __raw_spin_lock(&u->lock:0):
> > [ 7.013413] [<ffffffff81aa451f>] unix_stream_read_generic+0x6bf/0xb60
> > [ 7.013416] stacktrace:
> > [ 7.013416] _raw_spin_lock+0x6e/0x90
> > [ 7.013418] unix_stream_read_generic+0x6bf/0xb60
>
> It would be helpful if you'd run this through scripts/decode_stacktrace.sh
(Sorry for late reply, which was because of my email client issue.)
It was big help. Thank you very much.
> so we could see line numbers instead of hex offsets (which arene't much
> use without the binary kernel).
>
> > [ 7.013420] unix_stream_recvmsg+0x40/0x50
> > [ 7.013422] sock_read_iter+0x85/0xd0
> > [ 7.013424] new_sync_read+0x162/0x180
> > [ 7.013426] vfs_read+0xf3/0x190
> > [ 7.013428] ksys_read+0xa6/0xc0
> > [ 7.013429] do_syscall_64+0x3a/0x90
> > [ 7.013431] entry_SYSCALL_64_after_hwframe+0x44/0xae
> > [ 7.013433]
> > [ 7.013434] [W] wait(&(&ei->socket.wq.wait)->dmap:0):
> > [ 7.013434] [<ffffffff810bb017>] prepare_to_wait+0x47/0xd0
>
> ... this may be the source of confusion. Just because we prepare to
> wait doesn't mean we end up actually waiting. For example, look at
> unix_wait_for_peer():
>
> prepare_to_wait_exclusive(&u->peer_wait, &wait, TASK_INTERRUPTIBLE);
>
> sched = !sock_flag(other, SOCK_DEAD) &&
> !(other->sk_shutdown & RCV_SHUTDOWN) &&
> unix_recvq_full(other);
>
> unix_state_unlock(other);
>
> if (sched)
> timeo = schedule_timeout(timeo);
>
> finish_wait(&u->peer_wait, &wait);
>
> We *prepare* to wait, *then* drop the lock, then actually schedule.
Big help, too. I checked some samples for the usage, but where it's
almost "prepare == wait" :-(. Thanks a lot!
Thanks,
Byungchul
next prev parent reply other threads:[~2022-02-17 23:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-16 4:12 [REPORT] net deadlock possibilities by DEPT Byungchul Park
2022-02-16 4:17 ` Report in unix_stream_read_generic() Byungchul Park
2022-02-16 4:17 ` Report in unix_stream_sendmsg() Byungchul Park
2022-02-16 4:33 ` Report in unix_stream_read_generic() Matthew Wilcox
2022-02-17 23:50 ` Byungchul Park [this message]
2022-02-16 6:53 ` [REPORT] net deadlock possibilities by DEPT Byungchul Park
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