From: Andrew Morton <akpm@linux-foundation.org>
To: Qian Cai <cai@lca.pw>
Cc: mhocko@kernel.org, sergey.senozhatsky.work@gmail.com,
pmladek@suse.com, rostedt@goodmis.org, peterz@infradead.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_isolation: fix a deadlock with printk()
Date: Sat, 5 Oct 2019 17:44:23 -0700 [thread overview]
Message-ID: <20191005174423.23f2db80872a9365009f398a@linux-foundation.org> (raw)
In-Reply-To: <49F0AD04-6F61-4A1D-BFD5-E0769EC6F103@lca.pw>
On Sat, 5 Oct 2019 20:10:47 -0400 Qian Cai <cai@lca.pw> wrote:
>
>
> >> the existing dependency chain (in reverse order) is:
> >>
> >> -> #2 (&(&zone->lock)->rlock){-.-.}:
> >> lock_acquire+0x21a/0x468
> >> _raw_spin_lock+0x54/0x68
> >> get_page_from_freelist+0x8b6/0x2d28
> >> __alloc_pages_nodemask+0x246/0x658
> >> __get_free_pages+0x34/0x78
> >> sclp_init+0x106/0x690
> >> sclp_register+0x2e/0x248
> >> sclp_rw_init+0x4a/0x70
> >> sclp_console_init+0x4a/0x1b8
> >> console_init+0x2c8/0x410
> >> start_kernel+0x530/0x6a0
> >> startup_continue+0x70/0xd0
> >
> > This appears to be the core of our problem?
>
> No, that is just one of those many places could form the lock chain.
>
> console_lock -> other locks -> zone_lock
>
> Another example is,
>
> https://lore.kernel.org/lkml/1568823006.5576.178.camel@lca.pw/
There is no "console_lock". Please be much more specific.
> It is easier to avoid,
>
> zone_lock -> console_lock
>
> rather than fixing the opposite.
"ease" isn't the main objective. A more important question is "what
makes sense". We should be able to call printk() from anywhere, any
time under any conditions. That can't be done 100% but it is the
objective. printk() should be robust and not being able to call
printk() while holding zone->lock isn't robust!
btw, this:
: It is unsafe to call printk() while zone->lock was held, i.e.,
:
: zone->lock --> console_sem
doesn't make a lot of sense. console_sem is a sleeping lock so
attempting to acquire it (with down()!) under spinlock is a huge bug.
Again, please be careful with the descriptions.
next prev parent reply other threads:[~2019-10-06 0:44 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 16:42 Qian Cai
2019-10-04 17:47 ` David Hildenbrand
2019-10-04 18:53 ` Qian Cai
2019-10-05 23:29 ` Andrew Morton
2019-10-06 0:10 ` Qian Cai
2019-10-06 0:44 ` Andrew Morton [this message]
2019-10-06 1:10 ` Qian Cai
2019-10-06 1:56 ` Qian Cai
2019-10-06 0:59 ` Qian Cai
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