linux-kernel - RE: [PATCH] exfat: Avoid allocating upcase table using kcalloc()

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Date:   Wed, 2 Dec 2020 13:58:35 +0900
From:   "Sungjong Seo" <sj1557.seo@...sung.com>
To:     "'Artem Labazov'" <123321artyom@...il.com>
Cc:     <stable@...r.kernel.org>,
        "'Namjae Jeon'" <namjae.jeon@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] exfat: Avoid allocating upcase table using kcalloc()

> The table for Unicode upcase conversion requires an order-5 allocation,
> which may fail on a highly-fragmented system:
> 
>  pool-udisksd: page allocation failure: order:5,
> mode:0x40dc0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO),
> nodemask=(null),cpuset=/,mems_allowed=0
>  CPU: 4 PID: 3756880 Comm: pool-udisksd Tainted: G     U
5.8.10-
> 200.fc32.x86_64 #1
>  Hardware name: Dell Inc. XPS 13 9360/0PVG6D, BIOS 2.13.0 11/14/2019  Call
> Trace:
>   dump_stack+0x6b/0x88
>   warn_alloc.cold+0x75/0xd9
>   ? _cond_resched+0x16/0x40
>   ? __alloc_pages_direct_compact+0x144/0x150
>   __alloc_pages_slowpath.constprop.0+0xcfa/0xd30
>   ? __schedule+0x28a/0x840
>   ? __wait_on_bit_lock+0x92/0xa0
>   __alloc_pages_nodemask+0x2df/0x320
>   kmalloc_order+0x1b/0x80
>   kmalloc_order_trace+0x1d/0xa0
>   exfat_create_upcase_table+0x115/0x390 [exfat]
>   exfat_fill_super+0x3ef/0x7f0 [exfat]
>   ? sget_fc+0x1d0/0x240
>   ? exfat_init_fs_context+0x120/0x120 [exfat]
>   get_tree_bdev+0x15c/0x250
>   vfs_get_tree+0x25/0xb0
>   do_mount+0x7c3/0xaf0
>   ? copy_mount_options+0xab/0x180
>   __x64_sys_mount+0x8e/0xd0
>   do_syscall_64+0x4d/0x90
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Make the driver use vmalloc() to eliminate the issue.

I have not yet received a report of the same issue.
But I agree that this problem is likely to occur even if it is low
probability.

I think it would be more appropriate to use kvcalloc and kvfree instead.
Could you send me v2 patch?