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Message-ID: <71e66b02-9c2b-4981-83e1-8af72d6c0975@linux.alibaba.com>
Date: Thu, 18 Apr 2024 10:16:18 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: Baokun Li <libaokun1@...wei.com>, linux-erofs@...ts.ozlabs.org
Cc: 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
Subject: Re: [PATCH v2] erofs: reliably distinguish block based and fscache
mode
Hi Baokun,
Thanks for catching this and move forward fixing this!
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.
>
> 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.
>
> - 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);
--
Thanks,
Jingbo
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