From: Dmitry Safonov <dima@arista.com>
To: kernel test robot <rong.a.chen@intel.com>
Cc: linux-kernel@vger.kernel.org,
"Dmitry Safonov" <0x7f454c46@gmail.com>,
"Daniel Axtens" <dja@axtens.net>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Michael Neuling" <mikey@neuling.org>,
"Mikulas Patocka" <mpatocka@redhat.com>,
"Nathan March" <nathan@gt.net>, "Pasi Kärkkäinen" <pasik@iki.fi>,
"Peter Hurley" <peter@hurleysoftware.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Sergey Senozhatsky" <sergey.senozhatsky.work@gmail.com>,
"Tan Xiaojun" <tanxiaojun@huawei.com>,
"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
"Jiri Slaby" <jslaby@suse.cz>,
syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com,
stable@vger.kernel.org,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Jiri Slaby" <jslaby@suse.com>,
lkp@01.org
Subject: Re: [LKP] [tty] f26eb68a52: INFO:task_blocked_for_more_than#seconds
Date: Fri, 14 Sep 2018 16:56:49 +0100 [thread overview]
Message-ID: <1536940609.3185.29.camel@arista.com> (raw)
In-Reply-To: <20180914090151.GH7632@shao2-debian>
On Fri, 2018-09-14 at 17:01 +0800, kernel test robot wrote:
> FYI, we noticed the following commit (built with gcc-4.9):
Thanks,
[..]
> [ 245.080051] INFO: task lkp-setup-rootf:500 blocked for more than
> 120 seconds.
> [ 245.082850] Tainted: G W T 4.19.0-rc3-00014-
> gf26eb68 #1
> [ 245.084673] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [ 245.086455] lkp-setup-rootf D 6516 500 498 0x00000000
> [ 245.087766] Call Trace:
> [ 245.088391] __schedule+0x4b1/0xe80
> [ 245.089322] schedule+0x25/0x60
> [ 245.090178] schedule_timeout+0x275/0x4e0
> [ 245.091105] ? __ldsem_down_write_nested+0x1aa/0x300
> [ 245.092217] __ldsem_down_write_nested+0x1b2/0x300
> [ 245.093286] ? ldsem_down_write+0x2a/0x2e
> [ 245.094305] ldsem_down_write+0x2a/0x2e
> [ 245.095211] tty_ldisc_lock+0x16/0x40
> [ 245.096104] tty_reopen+0x3f/0xc0
> [ 245.096892] tty_open+0x3cf/0x450
> [ 245.097718] chrdev_open+0x9c/0x1f0
> [ 245.098511] ? security_file_open+0x99/0xa0
> [ 245.099512] do_dentry_open+0x3d5/0x5d0
> [ 245.100428] ? inode_permission+0x95/0x180
> [ 245.101351] ? cdev_put+0x30/0x30
> [ 245.102138] vfs_open+0x2d/0x30
> [ 245.102898] path_openat+0x9e1/0x17d0
> [ 245.103733] do_filp_open+0x6a/0x120
> [ 245.104541] ? _raw_spin_unlock+0x22/0x30
> [ 245.105439] ? __alloc_fd+0xa5/0x170
> [ 245.106309] do_sys_open+0x13a/0x250
> [ 245.107118] sys_open+0x22/0x30
> [ 245.107980] do_int80_syscall_32+0x94/0x1c0
> [ 245.108982] entry_INT80_32+0xf3/0xf3
So, unfortunately, I'll still have to set timeout to 5 sec for
tty_reopen(). The better fix would be to release read lock whenever a
writer is pending (say n_tty_receive_buf_common() can fallback), but
that's probably better to put in another patches set, as this one is
already packed.
Annoyingly, it means that open(tty) will have now more chances to fail
then before.. But still it's better than a panic with null-ptr deref.
--
Thanks,
Dmitry
next prev parent reply other threads:[~2018-09-14 15:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-12 0:16 [PATCHv4 0/7] tty: Hold write ldisc sem in tty_reopen() Dmitry Safonov
2018-09-12 0:16 ` [PATCHv4 1/7] tty: Drop tty->count on tty_reopen() failure Dmitry Safonov
2018-09-12 0:16 ` [PATCHv4 2/7] tty: Hold tty_ldisc_lock() during tty_reopen() Dmitry Safonov
2018-09-14 9:01 ` [LKP] [tty] f26eb68a52: INFO:task_blocked_for_more_than#seconds kernel test robot
2018-09-14 15:56 ` Dmitry Safonov [this message]
2018-09-12 0:16 ` [PATCHv4 3/7] tty/ldsem: Wake up readers after timed out down_write() Dmitry Safonov
2018-09-12 0:16 ` [PATCHv4 4/7] tty: Simplify tty->count math in tty_reopen() Dmitry Safonov
2018-09-12 0:16 ` [PATCHv4 5/7] tty/ldsem: Convert to regular lockdep annotations Dmitry Safonov
2018-09-12 0:17 ` [PATCHv4 6/7] tty/ldsem: Add lockdep asserts for ldisc_sem Dmitry Safonov
2018-09-12 0:17 ` [PATCHv4 7/7] tty/ldsem: Decrement wait_readers on timeouted down_read() Dmitry Safonov
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