Hi Changwei,
>>>
> Hi Gang,
>
> On 2018/3/29 10:36, Gang He wrote:
>> Hello Changwei,
>>
>>
>> Do you have the related crash backtrace?
> This patch has been pending in my tree for quite a long time and sadly I
> can't
> find the back trace right now. But we can still find the risk by reviewing
> related code. :)
>
>> Maybe I feel that new adding check is not necessary.
>
> Very true, but the check I add is for debug purpose.
> We can see that there are many places calling ocfs2_read_blocks(), some of
> them
> are passing only one bh while others are not.
> In order to handle potential exception easily, it's better for callers to
> pass
> bhs which are all null or assigned. So I add that trick to tell if some
> callers
> are doing stupid things.
>
> Thanks,
> Changwei
>
>> since the below code has make sure all buffer head is NOT NULL before
> reading block.
>> 216 ocfs2_metadata_cache_io_lock(ci);
>> 217 for (i = 0 ; i < nr ; i++) {
>> 218 if (bhs[i] == NULL) {
>> 219 bhs[i] = sb_getblk(sb, block++); <<= here
>> 220 if (bhs[i] == NULL) {
>> 221 ocfs2_metadata_cache_io_unlock(ci);
>> 222 status = -ENOMEM;
>> 223 mlog_errno(status);
>> 224 goto bail;
>> 225 }
>> 226 }
>> 227 bh = bhs[i];
>>
>>
>> Thanks
>> Gang
>>
>>
>>>>>
>>> ocfs2_read_blocks() is used to read several blocks from disk.
>>> Currently, the input argument *bhs* can be NULL or NOT. It depends on
>>> the caller's behavior. If the function fails in reading blocks from
>>> disk, the corresponding bh will be assigned to NULL and put.
>>>
>>> Obviously, above process for non-NULL input bh is not appropriate.
>>> Because the caller doesn't even know its bhs are put and re-assigned.
>>>
>>> If buffer head is managed by caller, ocfs2_read_blocks should not
>>> evaluate it to NULL. It will cause caller accessing illegal memory,
>>> thus crash.
>>>
>>> Signed-off-by: Changwei Ge <ge.chang...@h3c.com>
>>> ---
>>> fs/ocfs2/buffer_head_io.c | 31 +++++++++++++++++++++++++------
>>> 1 file changed, 25 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
>>> index d9ebe11..17329b6 100644
>>> --- a/fs/ocfs2/buffer_head_io.c
>>> +++ b/fs/ocfs2/buffer_head_io.c
>>> @@ -188,6 +188,7 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci, u64
>>> block, int nr,
>>> int i, ignore_cache = 0;
>>> struct buffer_head *bh;
>>> struct super_block *sb = ocfs2_metadata_cache_get_super(ci);
>>> + int new_bh = 0;
>>>
>>> trace_ocfs2_read_blocks_begin(ci, (unsigned long long)block, nr, flags);
>>>
>>> @@ -213,6 +214,18 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci,
>>> u64
>>> block, int nr,
>>> goto bail;
>>> }
>>>
>>> + /* Use below trick to check if all bhs are NULL or assigned.
>>> + * Basically, we hope all bhs are consistent so that we can
>>> + * handle exception easily.
>>> + */
>>> + new_bh = (bhs[0] == NULL);
>>> + for (i = 1 ; i < nr ; i++) {
>>> + if ((new_bh && bhs[i]) || (!new_bh && !bhs[i])) {
>>> + WARN(1, "Not all bhs are consistent\n");
>>> + break;
>>> + }
>>> + }
Maybe just adding a buffer head array check is OK?
If not consistent, give a warning.
why do we need the below code change?
since all head buffers are always NOT NULL.
Thanks
Gang
>>> +
>>> ocfs2_metadata_cache_io_lock(ci);
>>> for (i = 0 ; i < nr ; i++) {
>>> if (bhs[i] == NULL) {
>>> @@ -324,8 +337,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci,
>>> u64
>>> block, int nr,
>>> if (!(flags & OCFS2_BH_READAHEAD)) {
>>> if (status) {
>>> /* Clear the rest of the buffers on error */
>>> - put_bh(bh);
>>> - bhs[i] = NULL;
>>> + if (new_bh) {
>>> + put_bh(bh);
>>> + bhs[i] = NULL;
>>> + }
>>> continue;
>>> }
>>> /* We know this can't have changed as we hold the
>>> @@ -342,8 +357,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci,
>>> u64
>>> block, int nr,
>>> * for this bh as it's not marked locally
>>> * uptodate. */
>>> status = -EIO;
>>> - put_bh(bh);
>>> - bhs[i] = NULL;
>>> + if (new_bh) {
>>> + put_bh(bh);
>>> + bhs[i] = NULL;
>>> + }
>>> continue;
>>> }
>>>
>>> @@ -355,8 +372,10 @@ int ocfs2_read_blocks(struct ocfs2_caching_info *ci,
>>> u64
>>> block, int nr,
>>> clear_buffer_needs_validate(bh);
>>> status = validate(sb, bh);
>>> if (status) {
>>> - put_bh(bh);
>>> - bhs[i] = NULL;
>>> + if (new_bh) {
>>> + put_bh(bh);
>>> + bhs[i] = NULL;
>>> + }
>>> continue;
>>> }
>>> }
>>> --
>>> 2.7.4
>>>
>>>
>>> _______________________________________________
>>> Ocfs2-devel mailing list
>>> Ocfs2-devel@oss.oracle.com
>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>>
>>
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