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Date: Thu, 18 Apr 2024 11:36:03 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>
CC: <linux-erofs@...ts.ozlabs.org>, <xiang@...nel.org>, <chao@...nel.org>,
<huyue2@...lpad.com>, <viro@...iv.linux.org.uk>, <brauner@...nel.org>,
<linux-kernel@...r.kernel.org>, <yangerkun@...wei.com>, <houtao1@...wei.com>,
Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v2] erofs: reliably distinguish block based and fscache
mode
On 2024/4/18 10:16, Jingbo Xu wrote:
> Hi Baokun,
>
> Thanks for catching this and move forward fixing this!
Hi Jingbo，
Thanks for your review！
>
> On 4/17/24 2:55 PM, Baokun Li wrote:
>> When erofs_kill_sb() is called in block dev based mode, s_bdev may not have
>> been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled, it will
>> be mistaken for fscache mode, and then attempt to free an anon_dev that has
>> never been allocated, triggering the following warning:
>>
>> ============================================
>> ida_free called for id=0 which is not allocated.
>> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
>> Modules linked in:
>> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
>> RIP: 0010:ida_free+0x134/0x140
>> Call Trace:
>> <TASK>
>> erofs_kill_sb+0x81/0x90
>> deactivate_locked_super+0x35/0x80
>> get_tree_bdev+0x136/0x1e0
>> vfs_get_tree+0x2c/0xf0
>> do_new_mount+0x190/0x2f0
>> [...]
>> ============================================
>>
>> Instead of allocating the erofs_sb_info in fill_super() allocate it
>> during erofs_get_tree() and ensure that erofs can always have the info
>> available during erofs_kill_sb().
>
> I'm not sure if allocating erofs_sb_info in erofs_init_fs_context() will
> be better, as I see some filesystems (e.g. autofs) do this way. Maybe
> another potential advantage of doing this way is that erofs_fs_context
> is not needed anymore and we can use sbi directly.
Yes, except for some extra memory usage when remounting,
this idea sounds great. Let me send a version of v3 to get rid
of erofs_fs_context.
>
>> Signed-off-by: Christian Brauner <brauner@...nel.org>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> ---
>> Changes since v1:
>> Allocate and initialise fc->s_fs_info in erofs_fc_get_tree() instead of
>> modifying fc->sb_flags.
>>
>> V1: https://lore.kernel.org/r/20240415121746.1207242-1-libaokun1@huawei.com/
>>
>> fs/erofs/super.c | 51 ++++++++++++++++++++++++++----------------------
>> 1 file changed, 28 insertions(+), 23 deletions(-)
>>
>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>> index b21bd8f78dc1..4104280be2ea 100644
>> --- a/fs/erofs/super.c
>> +++ b/fs/erofs/super.c
>> @@ -581,8 +581,7 @@ static const struct export_operations erofs_export_ops = {
>> static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>> {
>> struct inode *inode;
>> - struct erofs_sb_info *sbi;
>> - struct erofs_fs_context *ctx = fc->fs_private;
>> + struct erofs_sb_info *sbi = EROFS_SB(sb);
>> int err;
>>
>> sb->s_magic = EROFS_SUPER_MAGIC;
>> @@ -590,19 +589,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>> sb->s_maxbytes = MAX_LFS_FILESIZE;
>> sb->s_op = &erofs_sops;
>>
>> - sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>> - if (!sbi)
>> - return -ENOMEM;
>> -
>> - sb->s_fs_info = sbi;
>> - sbi->opt = ctx->opt;
>> - sbi->devs = ctx->devs;
>> - ctx->devs = NULL;
>> - sbi->fsid = ctx->fsid;
>> - ctx->fsid = NULL;
>> - sbi->domain_id = ctx->domain_id;
>> - ctx->domain_id = NULL;
>> -
>> sbi->blkszbits = PAGE_SHIFT;
>> if (erofs_is_fscache_mode(sb)) {
>> sb->s_blocksize = PAGE_SIZE;
>> @@ -704,11 +690,32 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>> return 0;
>> }
>>
>> -static int erofs_fc_get_tree(struct fs_context *fc)
>> +static void erofs_ctx_to_info(struct fs_context *fc)
>> {
>> struct erofs_fs_context *ctx = fc->fs_private;
>> + struct erofs_sb_info *sbi = fc->s_fs_info;
>> +
>> + sbi->opt = ctx->opt;
>> + sbi->devs = ctx->devs;
>> + ctx->devs = NULL;
>> + sbi->fsid = ctx->fsid;
>> + ctx->fsid = NULL;
>> + sbi->domain_id = ctx->domain_id;
>> + ctx->domain_id = NULL;
>> +}
> I'm not sure if abstracting this logic into a seperate helper really
> helps understanding the code as the logic itself is quite simple and
> easy to be understood. Usually it's a hint of over-abstraction when a
> simple helper has only one caller.
>
Static functions that have only one caller are compiled inline, so we
don't have to worry about how that affects the code.
The reason these codes are encapsulated in a separate function is so
that the code reader understands that these codes are integrated
as a whole, and that we shouldn't have to move one or two of these
lines individually.
But after we get rid of erofs_fs_context, those won't be needed
anymore.
>>
>> - if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->fsid)
>> +static int erofs_fc_get_tree(struct fs_context *fc)
>> +{
>> + struct erofs_sb_info *sbi;
>> +
>> + sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>> + if (!sbi)
>> + return -ENOMEM;
>> +
>> + fc->s_fs_info = sbi;
>> + erofs_ctx_to_info(fc);
>> +
>> + if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>> return get_tree_nodev(fc, erofs_fc_fill_super);
>>
>> return get_tree_bdev(fc, erofs_fc_fill_super);
>> @@ -767,6 +774,7 @@ static void erofs_fc_free(struct fs_context *fc)
>> kfree(ctx->fsid);
>> kfree(ctx->domain_id);
>> kfree(ctx);
>> + kfree(fc->s_fs_info);
>> }
>>
>> static const struct fs_context_operations erofs_context_ops = {
>> @@ -783,6 +791,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
>> ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>> if (!ctx)
>> return -ENOMEM;
>> +
>> ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
>> if (!ctx->devs) {
>> kfree(ctx);
>> @@ -799,17 +808,13 @@ static int erofs_init_fs_context(struct fs_context *fc)
>>
>> static void erofs_kill_sb(struct super_block *sb)
>> {
>> - struct erofs_sb_info *sbi;
>> + struct erofs_sb_info *sbi = EROFS_SB(sb);
>>
>> - if (erofs_is_fscache_mode(sb))
>> + if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
>> kill_anon_super(sb);
>> else
>> kill_block_super(sb);
>>
>> - sbi = EROFS_SB(sb);
>> - if (!sbi)
>> - return;
>> -
>> erofs_free_dev_context(sbi->devs);
>> fs_put_dax(sbi->dax_dev, NULL);
>> erofs_fscache_unregister_fs(sb);
--
With Best Regards,
Baokun Li
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