Re: [PATCH v5 33/40] netfs, cachefiles: Pass upper bound length to allow expansion

Gao Xiang
2024-01-02T20:37:34Z

On 2024/1/3 01:11, David Howells wrote:
> Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>
>>> down = start - round_down(start, PAGE_SIZE);
>>> *_start = start - down;
>>> *_len = round_up(down + len, PAGE_SIZE);
>>> + if (down < start || *_len > upper_len)
>>> + return -ENOBUFS;
>>
>> Sorry for bothering. We just found some strange when testing
>> today-next EROFS over fscache.
>>
>> I'm not sure the meaning of
>> if (down < start
>>
>> For example, if start is page-aligned, down == 0.
>>
>> so as long as start > 0 and page-aligned, it will return
>> -ENOBUFS. Does it an intended behavior?
>
> Yeah, I think that's wrong.
>
> Does the attached help?

(+cc more people for testing)

Will test and feedback later.

Thanks,
Gao Xiang

>
> David
> ---
>
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index bffffedce4a9..7529b40bc95a 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -522,16 +522,22 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
> bool no_space_allocated_yet)
> {
> struct cachefiles_cache *cache = object->volume->cache;
> - loff_t start = *_start, pos;
> - size_t len = *_len, down;
> + unsigned long long start = *_start, pos;
> + size_t len = *_len;
> int ret;
>
> /* Round to DIO size */
> - down = start - round_down(start, PAGE_SIZE);
> - *_start = start - down;
> - *_len = round_up(down + len, PAGE_SIZE);
> - if (down < start || *_len > upper_len)
> + start = round_down(*_start, PAGE_SIZE);
> + if (start != *_start) {
> + kleave(" = -ENOBUFS [down]");
> + return -ENOBUFS;
> + }
> + if (*_len > upper_len) {
> + kleave(" = -ENOBUFS [up]");
> return -ENOBUFS;
> + }
> +
> + *_len = round_up(len, PAGE_SIZE);
>
> /* We need to work out whether there's sufficient disk space to perform
> * the write - but we can skip that check if we have space already
> @@ -542,7 +548,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>
> pos = cachefiles_inject_read_error();
> if (pos == 0)
> - pos = vfs_llseek(file, *_start, SEEK_DATA);
> + pos = vfs_llseek(file, start, SEEK_DATA);
> if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
> if (pos == -ENXIO)
> goto check_space; /* Unallocated tail */
> @@ -550,7 +556,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
> cachefiles_trace_seek_error);
> return pos;
> }
> - if ((u64)pos >= (u64)*_start + *_len)
> + if (pos >= start + *_len)
> goto check_space; /* Unallocated region */
>
> /* We have a block that's at least partially filled - if we're low on
> @@ -563,13 +569,13 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
>
> pos = cachefiles_inject_read_error();
> if (pos == 0)
> - pos = vfs_llseek(file, *_start, SEEK_HOLE);
> + pos = vfs_llseek(file, start, SEEK_HOLE);
> if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
> trace_cachefiles_io_error(object, file_inode(file), pos,
> cachefiles_trace_seek_error);
> return pos;
> }
> - if ((u64)pos >= (u64)*_start + *_len)
> + if (pos >= start + *_len)
> return 0; /* Fully allocated */
>
> /* Partially allocated, but insufficient space: cull. */
> @@ -577,7 +583,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
> ret = cachefiles_inject_remove_error();
> if (ret == 0)
> ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> - *_start, *_len);
> + start, *_len);
> if (ret < 0) {
> trace_cachefiles_io_error(object, file_inode(file), ret,
> cachefiles_trace_fallocate_error);
>