On 2023/7/10 11:37, Gao Xiang wrote:
On 2023/7/10 11:32, Chunhai Guo wrote:
Hi Xiang,
On 2023/7/8 17:00, Gao Xiang wrote:
Hi Chunhai,
On 2023/7/8 14:24, Chunhai Guo wrote:
When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
issues may occur:
- z_erofs_pcluster_readmore() may take a long time to loop when the offset
is big enough, which is unnecessary.
- For example, it will loop 4691368 times and take about 27 seconds
with following case.
- offset = 19217289215
- inode_size = 1442672
- z_erofs_do_read_page() may loop infinitely due to the inappropriate
truncation in the below statement. Since the offset is 64 bits and
min_t() truncates the result to 32 bits. The solution is to replace
unsigned int with another 64-bit type, such as erofs_off_t.
cur = end - min_t(unsigned int, offset + end - map->m_la, end);
- For example:
- offset = 0x400160000
- end = 0x370
- map->m_la = 0x160370
- offset + end - map->m_la = 0x400000000
- offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
Thanks for the catch!
Could you split these two into two patches?
how about using:
cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
for this?
since cur and end are all [0, PAGE_SIZE - 1] for now, and
folio_size() later.
OK. I will split the patch.
Sorry that I can not understand what is 'offend' refer to and what do you mean.
Could you please describe it more clearly?
Sorry, there is a typo here, I meant 'offset'.
`cur` and `end` both are not exceed 4096 if your page_size
is 4096.
Does
cur = end - min_t(erofs_off_t, offset + end - map->m_la, end)
fix your issue?
Yes. I think this will fix this issue. Do you mean the below change is
unncessary?
>>>> - unsigned int cur, end, spiltted;
>>>> + erofs_off_t cur, end;
>>>> + unsigned int spiltted;
- Expected result:
- cur = 0
- Actual result:
- cur = 0x370
Signed-off-by: Chunhai Guo <[email protected]>
---
fs/erofs/zdata.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5f1890e309c6..6abbd4510076 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct
z_erofs_decompress_frontend *fe,
struct erofs_map_blocks *const map = &fe->map;
const loff_t offset = page_offset(page);
bool tight = true, exclusive;
- unsigned int cur, end, spiltted;
+ erofs_off_t cur, end;
+ unsigned int spiltted;
int err = 0;
/* register locked file pages as online pages in pack */
@@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct
z_erofs_decompress_frontend *fe,
*/
tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
- cur = end - min_t(unsigned int, offset + end - map->m_la, end);
+ cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
if (!(map->m_flags & EROFS_MAP_MAPPED)) {
zero_user_segment(page, cur, end);
goto next_part;
@@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct
z_erofs_decompress_frontend *f,
}
cur = map->m_la + map->m_llen - 1;
- while (cur >= end) {
+ while ((cur >= end) && (cur < i_size_read(inode))) {
pgoff_t index = cur >> PAGE_SHIFT;
struct page *page;
@@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct
folio *folio)
trace_erofs_readpage(page, false);
f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
+ /* when trying to read beyond EOF, return zero page directly */
+ if (f.headoffset >= i_size_read(inode)) {
+ zero_user_segment(page, 0, PAGE_SIZE);
+ return 0;
+ }
Do we really need to optimize this rare case?
I guess the follow readmore fix is enough, thoughts? >
Thanks,
Gao Xiang
Since the code is constantly being updated and someone may encounter this bug
again, I think we had better fix it if possible.
z_erofs_do_read_page() already covers this case so I'm
not sure why we need to add another logic here.
You are right. I have removed this logic and sent the patch.
Thanks,
Gao Xiang
Thanks.
Guo Chunhai
