linux-kernel - Re: [PATCH] module/decompress: use vmalloc() for zstd decompression workspace

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Message-ID: <4ut44zckyknjwdzvxzefiysfjorl3nzqvs2j3scsrlgmgngjgs@hjrkcqoavq5h>
Date:   Tue, 29 Aug 2023 10:30:55 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
CC:     Andrea Righi <andrea.righi@...onical.com>,
        Nick Terrell <terrelln@...com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        <linux-modules@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] module/decompress: use vmalloc() for zstd decompression
 workspace

On Tue, Aug 29, 2023 at 09:41:32AM -0700, Luis Chamberlain wrote:
>On Tue, Aug 29, 2023 at 02:05:08PM +0200, Andrea Righi wrote:
>> Using kmalloc() to allocate the decompression workspace for zstd may
>> trigger the following warning when large modules are loaded (i.e., xfs):
>>
>> [    2.961884] WARNING: CPU: 1 PID: 254 at mm/page_alloc.c:4453 __alloc_pages+0x2c3/0x350
>> ...
>> [    2.989033] Call Trace:
>> [    2.989841]  <TASK>
>> [    2.990614]  ? show_regs+0x6d/0x80
>> [    2.991573]  ? __warn+0x89/0x160
>> [    2.992485]  ? __alloc_pages+0x2c3/0x350
>> [    2.993520]  ? report_bug+0x17e/0x1b0
>> [    2.994506]  ? handle_bug+0x51/0xa0
>> [    2.995474]  ? exc_invalid_op+0x18/0x80
>> [    2.996469]  ? asm_exc_invalid_op+0x1b/0x20
>> [    2.997530]  ? module_zstd_decompress+0xdc/0x2a0
>> [    2.998665]  ? __alloc_pages+0x2c3/0x350
>> [    2.999695]  ? module_zstd_decompress+0xdc/0x2a0
>> [    3.000821]  __kmalloc_large_node+0x7a/0x150
>> [    3.001920]  __kmalloc+0xdb/0x170
>> [    3.002824]  module_zstd_decompress+0xdc/0x2a0
>> [    3.003857]  module_decompress+0x37/0xc0
>> [    3.004688]  init_module_from_file+0xd0/0x100
>> [    3.005668]  idempotent_init_module+0x11c/0x2b0
>> [    3.006632]  __x64_sys_finit_module+0x64/0xd0
>> [    3.007568]  do_syscall_64+0x59/0x90
>> [    3.008373]  ? ksys_read+0x73/0x100
>> [    3.009395]  ? exit_to_user_mode_prepare+0x30/0xb0
>> [    3.010531]  ? syscall_exit_to_user_mode+0x37/0x60
>> [    3.011662]  ? do_syscall_64+0x68/0x90
>> [    3.012511]  ? do_syscall_64+0x68/0x90
>> [    3.013364]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>>
>> However, continuous physical memory does not seem to be required in
>> module_zstd_decompress(), so use vmalloc() instead, to prevent the
>> warning and avoid potential failures at loading compressed modules.
>>
>> Fixes: 169a58ad824d ("module/decompress: Support zstd in-kernel decompression")
>> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
>> ---
>>  kernel/module/decompress.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
>> index 8a5d6d63b06c..87440f714c0c 100644
>> --- a/kernel/module/decompress.c
>> +++ b/kernel/module/decompress.c
>> @@ -241,7 +241,7 @@ static ssize_t module_zstd_decompress(struct load_info *info,
>>  	}
>>
>>  	wksp_size = zstd_dstream_workspace_bound(header.windowSize);
>> -	wksp = kmalloc(wksp_size, GFP_KERNEL);
>> +	wksp = vmalloc(wksp_size);
>>  	if (!wksp) {
>>  		retval = -ENOMEM;
>>  		goto out;
>> @@ -284,7 +284,7 @@ static ssize_t module_zstd_decompress(struct load_info *info,
>>  	retval = new_size;
>>
>>   out:
>> -	kfree(wksp);
>> +	vfree(wksp);
>>  	return retval;
>
>Thanks! Applied and queued up.

I can see at least the gz decompress would need the same kind of change.
Shouldn't we tackle them all at once?

Lucas De Marchi

>
>  Luis