Re: FAILED: patch "[PATCH] mm/zsmalloc.c: drop ZSMALLOC_PGTABLE_MAPPING" failed to apply to 5.4-stable tree

[Minchan Kim <minchan@kernel.org>]

On Wed, Dec 09, 2020 at 10:07:04AM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From e91d8d78237de8d7120c320b3645b7100848f24d Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Sat, 5 Dec 2020 22:14:51 -0800
> Subject: [PATCH] mm/zsmalloc.c: drop ZSMALLOC_PGTABLE_MAPPING
> 
> 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.
> 
>   BUG: sleeping function called from invalid context at mm/vmalloc.c:108
>   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 946, name: memhog
>   3 locks held by memhog/946:
>    #0: ffff9d01d4b193e8 (&mm->mmap_lock#2){++++}-{4:4}, at: __mm_populate+0x103/0x160
>    #1: ffffffffa3d53de0 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0xa98/0x1160
>    #2: ffff9d01d56b8110 (&zspage->lock){.+.+}-{3:3}, at: zs_map_object+0x8e/0x1f0
>   CPU: 0 PID: 946 Comm: memhog Not tainted 5.9.3-00011-gc5bfc0287345-dirty #316
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
>   Call Trace:
>     unmap_kernel_range_noflush+0x2eb/0x350
>     unmap_kernel_range+0x14/0x30
>     zs_unmap_object+0xd5/0xe0
>     zram_bvec_rw.isra.0+0x38c/0x8e0
>     zram_rw_page+0x90/0x101
>     bdev_write_page+0x92/0xe0
>     __swap_writepage+0x94/0x4a0
>     pageout+0xe3/0x3a0
>     shrink_page_list+0xb94/0xd60
>     shrink_inactive_list+0x158/0x460
> 
> We can fix this by removing the ZSMALLOC_PGTABLE_MAPPING feature (which
> contains the offending calling code) from zsmalloc.
> 
> Even though this option showed some amount improvement(e.g., 30%) in
> some arm32 platforms, it has been headache to maintain since it have
> abused APIs[1](e.g., unmap_kernel_range in atomic context).
> 
> Since we are approaching to deprecate 32bit machines and already made
> the config option available for only builtin build since v5.8, lastly it
> has been not default option in zsmalloc, it's time to drop the option
> for better maintenance.
> 
> [1] http://lore.kernel.org/linux-mm/20201105170249.387069-1-minchan@kernel.org
> 
> Fixes: e47110e90584 ("mm/vunmap: add cond_resched() in vunmap_pmd_range")

This patch fixex e47110e90584 which merged at v5.9 so we could drop it
for v5.4.

Thanks.