On 2019/6/10 1:52 上午, Pierre JUHEN wrote:
> I tested a patched bcache module. OK for me.
hi Pierre,
Cool, thank you!
Coly Li
>
> Le 09/06/2019 à 17:28, Coly Li a écrit :
>> On 2019/6/9 11:24 下午, Coly Li wrote:
>>> Recently people report bcache code compiled with gcc9 is broken, one of
>>> the buggy behavior I observe is that two adjacent 4KB I/Os should merge
>>> into one but they don't. Finally it turns out to be a stack corruption
>>> caused by macro PRECEDING_KEY().
>>>
>>> See how PRECEDING_KEY() is defined in bset.h,
>>> 437 #define PRECEDING_KEY(_k) \
>>> 438 ({ \
>>> 439 struct bkey *_ret = NULL; \
>>> 440 \
>>> 441 if (KEY_INODE(_k) || KEY_OFFSET(_k)) { \
>>> 442 _ret = &KEY(KEY_INODE(_k), KEY_OFFSET(_k), 0); \
>>> 443 \
>>> 444 if (!_ret->low) \
>>> 445 _ret->high--; \
>>> 446 _ret->low--; \
>>> 447 } \
>>> 448 \
>>> 449 _ret; \
>>> 450 })
>>>
>>> At line 442, _ret points to address of a on-stack variable combined by
>>> KEY(), the life range of this on-stack variable is in line 442-446,
>>> once _ret is returned to bch_btree_insert_key(), the returned address
>>> points to an invalid stack address and this address is overwritten in
>>> the following called bch_btree_iter_init(). Then argument 'search' of
>>> bch_btree_iter_init() points to some address inside stackframe of
>>> bch_btree_iter_init(), exact address depends on how the compiler
>>> allocates stack space. Now the stack is corrupted.
>>>
>>> Signed-off-by: Coly Li <colyli@xxxxxxx>
>>> Reviewed-by: Rolf Fokkens <rolf@xxxxxxxxxxxxxx>
>>> Reviewed-by: Pierre JUHEN <pierre.juhen@xxxxxxxxx>
>> Hi Rolf and Pierre,
>>
>> Oops, I am a little bit too hurry, just realize you don't offer
>> Reviewed-by: yet.
>>
>> Could you like to offer a Reviewed-by: to this patch, then I may submit
>> to Jens in this run ASAP.
>>
>> Many thanks of your code review and help !
>>
>> Coly Li
>>
>>
>>> Tested-by: Shenghui Wang <shhuiw@xxxxxxxxxxx>
>>> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
>>> Cc: Nix <nix@xxxxxxxxxxxxx>
>>> ---
>>> Changlog:
>>> V2: Fix a pointer assignment problem in preceding_key(), which is
>>> pointed by Rolf Fokkens and Pierre JUHEN.
>>> V1: Initial RFC patch for review and comment.
>>>
>>> drivers/md/bcache/bset.c | 16 +++++++++++++---
>>> drivers/md/bcache/bset.h | 34 ++++++++++++++++++++--------------
>>> 2 files changed, 33 insertions(+), 17 deletions(-)
>> [snipped]
