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]
