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Message-ID: <1570193776.5576.270.camel@lca.pw>
Date: Fri, 04 Oct 2019 08:56:16 -0400
From: Qian Cai <cai@....pw>
To: Anshuman Khandual <anshuman.khandual@....com>,
Michal Hocko <mhocko@...nel.org>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Oscar Salvador <osalvador@...e.de>,
Mel Gorman <mgorman@...hsingularity.net>,
Mike Rapoport <rppt@...ux.ibm.com>,
Dan Williams <dan.j.williams@...el.com>,
Pavel Tatashin <pavel.tatashin@...rosoft.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in
has_unmovable_pages()
On Fri, 2019-10-04 at 17:14 +0530, Anshuman Khandual wrote:
>
> On 10/04/2019 04:28 PM, Michal Hocko wrote:
> > On Thu 03-10-19 13:40:57, Anshuman Khandual wrote:
> > > Having unmovable pages on a given pageblock should be reported correctly
> > > when required with REPORT_FAILURE flag. But there can be a scenario where a
> > > reserved page in the page block will get reported as a generic "unmovable"
> > > reason code. Instead this should be changed to a more appropriate reason
> > > code like "Reserved page".
> >
> > Others have already pointed out this is just redundant but I will have a
>
> Sure.
>
> > more generic comment on the changelog. There is essentially no
> > information why the current state is bad/unhelpful and why the chnage is
>
> The current state is not necessarily bad or unhelpful. I just though that it
> could be improved upon. Some how calling out explicitly only the CMA page
> failure case just felt adhoc, where as there are other reasons like HugeTLB
> immovability which might depend on other factors apart from just page flags
> (though I did not propose that originally).
>
> > needed. All you claim is that something is a certain way and then assert
> > that it should be done differently. That is not how changelogs should
> > look like.
> >
>
> Okay, probably I should have explained more on why "unmovable" is less than
> adequate to capture the exact reason for specific failure cases and how
> "Reserved Page" instead would been better. But got the point, will improve.
>
It might be a good time to rethink if it is really a good idea to dump_page()
at all inside has_unmovable_pages(). As it is right now, it is a a potential
deadlock between console vs memory offline. More details are in this thread,
https://lore.kernel.org/lkml/1568817579.5576.172.camel@lca.pw/
01: [ 672.875392] WARNING: possible circular locking dependency detected
01: [ 672.875394] 5.4.0-rc1-next-20191004+ #64 Not tainted
01: [ 672.875396] ------------------------------------------------------
01: [ 672.875398] test.sh/1724 is trying to acquire lock:
01: [ 672.875400] 0000000052059ec0 (console_owner){-...}, at: console_unlock+0x
01: 328/0xa30
01: [ 672.875406]
01: [ 672.875408] but task is already holding lock:
01: [ 672.875409] 000000006ffd89c8 (&(&zone->lock)->rlock){-.-.}, at: start_iso
01: late_page_range+0x216/0x538
01: [ 672.875415]
01: [ 672.875417] which lock already depends on the new lock.
01: [ 672.875418]
01: [ 672.875419]
01: [ 672.875421] the existing dependency chain (in reverse order) is:
01: [ 672.875423]
01: [ 672.875424] -> #2 (&(&zone->lock)->rlock){-.-.}:
01: [ 672.875430] lock_acquire+0x21a/0x468
01: [ 672.875431] _raw_spin_lock+0x54/0x68
01: [ 672.875433] get_page_from_freelist+0x8b6/0x2d28
01: [ 672.875435] __alloc_pages_nodemask+0x246/0x658
01: [ 672.875437] __get_free_pages+0x34/0x78
01: [ 672.875438] sclp_init+0x106/0x690
01: [ 672.875440] sclp_register+0x2e/0x248
01: [ 672.875442] sclp_rw_init+0x4a/0x70
01: [ 672.875443] sclp_console_init+0x4a/0x1b8
01: [ 672.875445] console_init+0x2c8/0x410
01: [ 672.875447] start_kernel+0x530/0x6a0
01: [ 672.875448] startup_continue+0x70/0xd0
01: [ 672.875449]
01: [ 672.875450] -> #1 (sclp_lock){-.-.}:
01: [ 672.875458] lock_acquire+0x21a/0x468
01: [ 672.875460] _raw_spin_lock_irqsave+0xcc/0xe8
01: [ 672.875462] sclp_add_request+0x34/0x308
01: [ 672.875464] sclp_conbuf_emit+0x100/0x138
01: [ 672.875465] sclp_console_write+0x96/0x3b8
01: [ 672.875467] console_unlock+0x6dc/0xa30
01: [ 672.875469] vprintk_emit+0x184/0x3c8
01: [ 672.875470] vprintk_default+0x44/0x50
01: [ 672.875472] printk+0xa8/0xc0
01: [ 672.875473] iommu_debugfs_setup+0xf2/0x108
01: [ 672.875475] iommu_init+0x6c/0x78
01: [ 672.875477] do_one_initcall+0x162/0x680
01: [ 672.875478] kernel_init_freeable+0x4e8/0x5a8
01: [ 672.875480] kernel_init+0x2a/0x188
01: [ 672.875484] ret_from_fork+0x30/0x34
01: [ 672.875486] kernel_thread_starter+0x0/0xc
01: [ 672.875487]
01: [ 672.875488] -> #0 (console_owner){-...}:
01: [ 672.875495] check_noncircular+0x338/0x3e0
01: [ 672.875496] __lock_acquire+0x1e66/0x2d88
01: [ 672.875498] lock_acquire+0x21a/0x468
01: [ 672.875499] console_unlock+0x3a6/0xa30
01: [ 672.875501] vprintk_emit+0x184/0x3c8
01: [ 672.875503] vprintk_default+0x44/0x50
01: [ 672.875504] printk+0xa8/0xc0
01: [ 672.875506] __dump_page+0x1dc/0x710
01: [ 672.875507] dump_page+0x2e/0x58
01: [ 672.875509] has_unmovable_pages+0x2e8/0x470
01: [ 672.875511] start_isolate_page_range+0x404/0x538
01: [ 672.875513] __offline_pages+0x22c/0x1338
01: [ 672.875514] memory_subsys_offline+0xa6/0xe8
01: [ 672.875516] device_offline+0xe6/0x118
01: [ 672.875517] state_store+0xf0/0x110
01: [ 672.875519] kernfs_fop_write+0x1bc/0x270
01: [ 672.875521] vfs_write+0xce/0x220
01: [ 672.875522] ksys_write+0xea/0x190
01: [ 672.875524] system_call+0xd8/0x2b4
01: [ 672.875525]
01: [ 672.875527] other info that might help us debug this:
01: [ 672.875528]
01: [ 672.875529] Chain exists of:
01: [ 672.875530] console_owner --> sclp_lock --> &(&zone->lock)->rlock
01: [ 672.875538]
01: [ 672.875540] Possible unsafe locking scenario:
01: [ 672.875541]
01: [ 672.875543] CPU0 CPU1
01: [ 672.875544] ---- ----
01: [ 672.875545] lock(&(&zone->lock)->rlock);
01: [ 672.875549] lock(sclp_lock);
01: [ 672.875553] lock(&(&zone->lock)->rlock);
01: [ 672.875557] lock(console_owner);
01: [ 672.875560]
01: [ 672.875562] *** DEADLOCK ***
01: [ 672.875563]
01: [ 672.875564] 9 locks held by test.sh/1724:
01: [ 672.875565] #0: 000000000e925408 (sb_writers#4){.+.+}, at: vfs_write+0x2
01: 06/0x220
01: [ 672.875574] #1: 0000000050aa4280 (&of->mutex){+.+.}, at: kernfs_fop_writ
01: e+0x154/0x270
01: [ 672.875581] #2: 0000000062e5c628 (kn->count#198){.+.+}, at: kernfs_fop_w
01: rite+0x16a/0x270
01: [ 672.875590] #3: 00000000523236a0 (device_hotplug_lock){+.+.}, at: lock_d
01: evice_hotplug_sysfs+0x30/0x80
01: [ 672.875598] #4: 0000000062e70990 (&dev->mutex){....}, at: device_offline
01: +0x78/0x118
01: [ 672.875605] #5: 0000000051fd36b0 (cpu_hotplug_lock.rw_sem){++++}, at: __
01: offline_pages+0xec/0x1338
01: [ 672.875613] #6: 00000000521ca470 (mem_hotplug_lock.rw_sem){++++}, at: pe
01: rcpu_down_write+0x38/0x210
01: [ 672.875620] #7: 000000006ffd89c8 (&(&zone->lock)->rlock){-.-.}, at: star
01: t_isolate_page_range+0x216/0x538
01: [ 672.875628] #8: 000000005205a100 (console_lock){+.+.}, at: vprintk_emit+
01: 0x178/0x3c8
01: [ 672.875635]
01: [ 672.875636] stack backtrace:
01: [ 672.875639] CPU: 1 PID: 1724 Comm: test.sh Not tainted 5.4.0-rc1-next-201
01: 91004+ #64
01: [ 672.875640] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)
01: [ 672.875642] Call Trace:
01: [ 672.875644] ([<00000000512ae218>] show_stack+0x110/0x1b0)
01: [ 672.875645] [<0000000051b6d506>] dump_stack+0x126/0x178
01: [ 672.875648] [<00000000513a4b08>] check_noncircular+0x338/0x3e0
01: [ 672.875650] [<00000000513aaaf6>] __lock_acquire+0x1e66/0x2d88
01: [ 672.875652] [<00000000513a7e12>] lock_acquire+0x21a/0x468
01: [ 672.875654] [<00000000513bb2fe>] console_unlock+0x3a6/0xa30
01: [ 672.875655] [<00000000513bde2c>] vprintk_emit+0x184/0x3c8
01: [ 672.875657] [<00000000513be0b4>] vprintk_default+0x44/0x50
01: [ 672.875659] [<00000000513beb60>] printk+0xa8/0xc0
01: [ 672.875661] [<000000005158c364>] __dump_page+0x1dc/0x710
01: [ 672.875663] [<000000005158c8c6>] dump_page+0x2e/0x58
01: [ 672.875665] [<00000000515d87c8>] has_unmovable_pages+0x2e8/0x470
01: [ 672.875667] [<000000005167072c>] start_isolate_page_range+0x404/0x538
01: [ 672.875669] [<0000000051b96de4>] __offline_pages+0x22c/0x1338
01: [ 672.875671] [<0000000051908586>] memory_subsys_offline+0xa6/0xe8
01: [ 672.875673] [<00000000518e561e>] device_offline+0xe6/0x118
01: [ 672.875675] [<0000000051908170>] state_store+0xf0/0x110
01: [ 672.875677] [<0000000051796384>] kernfs_fop_write+0x1bc/0x270
01: [ 672.875679] [<000000005168972e>] vfs_write+0xce/0x220
01: [ 672.875681] [<0000000051689b9a>] ksys_write+0xea/0x190
01: [ 672.875685] [<0000000051ba9990>] system_call+0xd8/0x2b4
01: [ 672.875687] INFO: lockdep is turned off.
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