From: Minchan Kim <minchan@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Harish Sriram <harish@linux.ibm.com>,
stable@vger.kernel.org
Subject: Re: [PATCH] Revert "mm/vunmap: add cond_resched() in vunmap_pmd_range"
Date: Sat, 7 Nov 2020 00:39:39 -0800 [thread overview]
Message-ID: <20201107083939.GA1633068@google.com> (raw)
In-Reply-To: <20201106175933.90e4c8851010c9ce4dd732b6@linux-foundation.org>
Hi Andrew,
On Fri, Nov 06, 2020 at 05:59:33PM -0800, Andrew Morton wrote:
> On Thu, 5 Nov 2020 09:02:49 -0800 Minchan Kim <minchan@kernel.org> wrote:
>
> > This reverts commit e47110e90584a22e9980510b00d0dfad3a83354e.
> >
> > While I was doing zram testing, I found sometimes decompression failed
> > since the compression buffer was corrupted. With investigation,
> > I found below commit calls cond_resched unconditionally so it could
> > make a problem in atomic context if the task is reschedule.
> >
> > Revert the original commit for now.
> >
> > [ 55.109012] BUG: sleeping function called from invalid context at mm/vmalloc.c:108
> > [ 55.110774] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 946, name: memhog
> > [ 55.111973] 3 locks held by memhog/946:
> > [ 55.112807] #0: ffff9d01d4b193e8 (&mm->mmap_lock#2){++++}-{4:4}, at: __mm_populate+0x103/0x160
> > [ 55.114151] #1: ffffffffa3d53de0 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0xa98/0x1160
> > [ 55.115848] #2: ffff9d01d56b8110 (&zspage->lock){.+.+}-{3:3}, at: zs_map_object+0x8e/0x1f0
> > [ 55.118947] CPU: 0 PID: 946 Comm: memhog Not tainted 5.9.3-00011-gc5bfc0287345-dirty #316
> > [ 55.121265] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
> > [ 55.122540] Call Trace:
> > [ 55.122974] dump_stack+0x8b/0xb8
> > [ 55.123588] ___might_sleep.cold+0xb6/0xc6
> > [ 55.124328] unmap_kernel_range_noflush+0x2eb/0x350
> > [ 55.125198] unmap_kernel_range+0x14/0x30
> > [ 55.125920] zs_unmap_object+0xd5/0xe0
> > [ 55.126604] zram_bvec_rw.isra.0+0x38c/0x8e0
> > [ 55.127462] zram_rw_page+0x90/0x101
> > [ 55.128199] bdev_write_page+0x92/0xe0
> > [ 55.128957] ? swap_slot_free_notify+0xb0/0xb0
> > [ 55.129841] __swap_writepage+0x94/0x4a0
> > [ 55.130636] ? do_raw_spin_unlock+0x4b/0xa0
> > [ 55.131462] ? _raw_spin_unlock+0x1f/0x30
> > [ 55.132261] ? page_swapcount+0x6c/0x90
> > [ 55.133038] pageout+0xe3/0x3a0
> > [ 55.133702] shrink_page_list+0xb94/0xd60
> > [ 55.134626] shrink_inactive_list+0x158/0x460
> >
> > ...
> >
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -102,8 +102,6 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
> > if (pmd_none_or_clear_bad(pmd))
> > continue;
> > vunmap_pte_range(pmd, addr, next, mask);
> > -
> > - cond_resched();
> > } while (pmd++, addr = next, addr != end);
> > }
>
> If this is triggering a warning then why isn't the might_sleep() in
> remove_vm_area() also triggering?
I don't understand what specific callpath you are talking but if
it's clearly called in atomic context, the reason would be config
combination I met.
CONFIG_PREEMPT_VOLUNTARY + no CONFIG_DEBUG_ATOMIC_SLEEP
It makes preempt_count logic void so might_sleep warning will not work.
>
> Sigh. I also cannot remember why these vfree() functions have to be so
> awkward. The mutex_trylock(&vmap_purge_lock) isn't permitted in
> interrupt context because mutex_trylock() is stupid, but what was the
> issue with non-interrupt atomic code?
>
Seems like a latency issue.
commit f9e09977671b
Author: Christoph Hellwig <hch@lst.de>
Date: Mon Dec 12 16:44:23 2016 -0800
mm: turn vmap_purge_lock into a mutex
The purge_lock spinlock causes high latencies with non RT kernel,
next prev parent reply other threads:[~2020-11-07 8:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-05 17:02 [PATCH] Revert "mm/vunmap: add cond_resched() in vunmap_pmd_range" Minchan Kim
2020-11-05 17:16 ` Matthew Wilcox
2020-11-05 17:33 ` Minchan Kim
2020-11-07 1:59 ` Andrew Morton
2020-11-07 8:39 ` Minchan Kim [this message]
2020-11-09 11:33 ` Uladzislau Rezki
2020-11-12 20:01 ` Minchan Kim
2020-11-12 22:49 ` Andrew Morton
2020-11-13 16:25 ` Minchan Kim
2020-11-16 17:53 ` Minchan Kim
2020-11-16 23:20 ` Andrew Morton
2020-11-17 13:57 ` Uladzislau Rezki
2020-11-17 13:56 ` Christoph Hellwig
2020-11-17 20:29 ` Minchan Kim
2020-11-18 2:06 ` Sergey Senozhatsky
2020-11-19 9:29 ` Tony Lindgren
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