In buffer-only mode, relay_open(NULL, NULL, ...) is used to create the
buffer first, where chan->has_base_filename is not set. Though we still
need to call chan->cb->create_buf_file in relay_open_buf() to retrieve
global info for global buffer, the create_buf_file callback should
return NULL. With IS_ERR_OR_NULL() check, relay_open fails because of
the returned NULL dentry, so this patch reverts back to the WARN_ON()
version and add a comment for this behavior.
Here is an example after fix:
```
struct dentry *my_create_buf_file(const char *filename,
struct dentry *parent, umode_t mode,
struct rchan_buf *buf, int *is_global)
{
if (!filename)
return NULL;
return debugfs_create_file(filename, mode, parent, buf,
&relay_file_operations);
}
relay_cb.create_buf_file = my_create_buf_file
relay_chan = relay_open(NULL, NULL,
subbuf_size, subbuf_num,
&relay_cb, NULL);
relay_late_setup_files(relay_chan, filename, parent);
```
But before fix, the create_buf_file callback must be something like:
```
struct dentry *my_create_buf_file(const char *filename,
struct dentry *parent, umode_t mode,
struct rchan_buf *buf, int *is_global)
{
if (!filename)
return ERR_PTR(1); // a valid ptr is necessary for relay_open
return debugfs_create_file(filename, mode, parent, buf,
&relay_file_operations);
}
```
I'm not sure if this revertion proper because it may break existing use
cases. I think we can also remove the WARN_ON check instead.
Fixes: 2c1cf00eeacb ("relay: check return of create_buf_file() properly")
Signed-off-by: Philo Lu <[email protected]>
---
kernel/relay.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/relay.c b/kernel/relay.c
index 83fe0325cde1..0700745447c1 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -395,7 +395,8 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
dentry = chan->cb->create_buf_file(NULL, NULL,
S_IRUSR, buf,
&chan->is_global);
- if (IS_ERR_OR_NULL(dentry))
+ /* has_base_filename not set, so dentry should be NULL */
+ if (WARN_ON(dentry))
goto free_buf;
}
--
2.32.0.3.g01195cf9f
Sorry, the email address of Andrew was wrongly spelled, so CC again.
On 2023/12/20 15:47, Philo Lu wrote:
> In buffer-only mode, relay_open(NULL, NULL, ...) is used to create the
> buffer first, where chan->has_base_filename is not set. Though we still
> need to call chan->cb->create_buf_file in relay_open_buf() to retrieve
> global info for global buffer, the create_buf_file callback should
> return NULL. With IS_ERR_OR_NULL() check, relay_open fails because of
> the returned NULL dentry, so this patch reverts back to the WARN_ON()
> version and add a comment for this behavior.
>
> Here is an example after fix:
> ```
> struct dentry *my_create_buf_file(const char *filename,
> struct dentry *parent, umode_t mode,
> struct rchan_buf *buf, int *is_global)
> {
> if (!filename)
> return NULL;
>
> return debugfs_create_file(filename, mode, parent, buf,
> &relay_file_operations);
> }
>
> relay_cb.create_buf_file = my_create_buf_file
> relay_chan = relay_open(NULL, NULL,
> subbuf_size, subbuf_num,
> &relay_cb, NULL);
> relay_late_setup_files(relay_chan, filename, parent);
> ```
>
> But before fix, the create_buf_file callback must be something like:
> ```
> struct dentry *my_create_buf_file(const char *filename,
> struct dentry *parent, umode_t mode,
> struct rchan_buf *buf, int *is_global)
> {
> if (!filename)
> return ERR_PTR(1); // a valid ptr is necessary for relay_open
>
> return debugfs_create_file(filename, mode, parent, buf,
> &relay_file_operations);
> }
> ```
>
> I'm not sure if this revertion proper because it may break existing use
> cases. I think we can also remove the WARN_ON check instead.
>
> Fixes: 2c1cf00eeacb ("relay: check return of create_buf_file() properly")
> Signed-off-by: Philo Lu <[email protected]>
> ---
> kernel/relay.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/relay.c b/kernel/relay.c
> index 83fe0325cde1..0700745447c1 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -395,7 +395,8 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
> dentry = chan->cb->create_buf_file(NULL, NULL,
> S_IRUSR, buf,
> &chan->is_global);
> - if (IS_ERR_OR_NULL(dentry))
> + /* has_base_filename not set, so dentry should be NULL */
> + if (WARN_ON(dentry))
> goto free_buf;
> }
>
> --
> 2.32.0.3.g01195cf9f
Hi all,
Is there any feedback about this patch?
Many thanks for your time.