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V" , Harish Sriram , stable@vger.kernel.org Subject: Re: [PATCH] Revert "mm/vunmap: add cond_resched() in vunmap_pmd_range" Message-ID: <20201107083939.GA1633068@google.com> References: <20201105170249.387069-1-minchan@kernel.org> <20201106175933.90e4c8851010c9ce4dd732b6@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201106175933.90e4c8851010c9ce4dd732b6@linux-foundation.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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 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 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,