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

From: Sungjong Seo
Date: Tue Dec 01 2020 - 23:59:33 EST


> 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?