* [PATCH] md: bcache: fix error return code of cached_dev_cache_miss() @ 2021-03-05 2:46 Jia-Ju Bai 2021-03-05 4:05 ` Coly Li 0 siblings, 1 reply; 3+ messages in thread From: Jia-Ju Bai @ 2021-03-05 2:46 UTC (permalink / raw) To: colyli, kent.overstreet; +Cc: linux-bcache, linux-kernel, Jia-Ju Bai When bch_bio_alloc_pages() fails, no error return code of cached_dev_cache_miss() is assigned. To fix this bug, ret is assigned with -ENOMEN as error return code. Reported-by: TOTE Robot <oslab@tsinghua.edu.cn> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> --- drivers/md/bcache/request.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index 29c231758293..9ecaf26c8d60 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -930,8 +930,10 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s, cache_bio->bi_private = &s->cl; bch_bio_map(cache_bio, NULL); - if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) + if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) { + ret = -ENOMEM; goto out_put; + } if (reada) bch_mark_cache_readahead(s->iop.c, s->d); -- 2.17.1 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] md: bcache: fix error return code of cached_dev_cache_miss() 2021-03-05 2:46 [PATCH] md: bcache: fix error return code of cached_dev_cache_miss() Jia-Ju Bai @ 2021-03-05 4:05 ` Coly Li 2021-03-05 7:28 ` Jia-Ju Bai 0 siblings, 1 reply; 3+ messages in thread From: Coly Li @ 2021-03-05 4:05 UTC (permalink / raw) To: Jia-Ju Bai; +Cc: linux-bcache, linux-kernel, kent.overstreet On 3/5/21 10:46 AM, Jia-Ju Bai wrote: > When bch_bio_alloc_pages() fails, no error return code of > cached_dev_cache_miss() is assigned. > To fix this bug, ret is assigned with -ENOMEN as error return code. > > Reported-by: TOTE Robot <oslab@tsinghua.edu.cn> > Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> > --- > drivers/md/bcache/request.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c > index 29c231758293..9ecaf26c8d60 100644 > --- a/drivers/md/bcache/request.c > +++ b/drivers/md/bcache/request.c > @@ -930,8 +930,10 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s, > cache_bio->bi_private = &s->cl; > > bch_bio_map(cache_bio, NULL); > - if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) > + if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) { > + ret = -ENOMEM; > goto out_put; > + } > > if (reada) > bch_mark_cache_readahead(s->iop.c, s->d); > Thanks for looking at bcache :-) Without the above change, -EINTR will be returned. -EINTR is special in bache's btree iteration code. See bcache_btree_root() from bcache.h, 347 #define bcache_btree_root(fn, c, op, ...) \ 348 ({ \ 349 int _r = -EINTR; \ 350 do { \ 351 struct btree *_b = (c)->root; \ 352 bool _w = insert_lock(op, _b); \ 353 rw_lock(_w, _b, _b->level); \ 354 if (_b == (c)->root && \ 355 _w == insert_lock(op, _b)) { \ 356 _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \ 357 } \ 358 rw_unlock(_w, _b); \ 359 bch_cannibalize_unlock(c); \ 360 if (_r == -EINTR) \ 361 \ 362 } while (_r == -EINTR); \ 363 \ 364 finish_wait(&(c)->btree_cache_wait, &(op)->wait); \ 365 _r; \ 366 }) cached_dev_cache_miss() is called by the following code path, cache_lookup() ==> bch_btree_map_keys() ==> bcache_btree_root() ==> bch_btree_map_keys_recurse() ==> cache_lookup_fn() Therefore the return value of cached_dev_cache_miss() will be returned from where s->d->cache_miss() is called from cache_lookup_fn(). And in macro bcache_btree_root() this return value will be checked. If the return value is -EINTR, then the whole iteration will be re-do again. Returning -ENOMEM works but if the memory allocation failed, there is no chance to re-do the cache lookup again from bcache_btree_root(). When system memory is in heavy usage, we want the lookup to try more times (because GFP_NOIO is set), which is much better then returning -EIO immediately to caller. Therefore NOT setting ret to -ENOMEM in the patching location should be an on-purpose coding, IMHO. Thanks. Coly Li ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] md: bcache: fix error return code of cached_dev_cache_miss() 2021-03-05 4:05 ` Coly Li @ 2021-03-05 7:28 ` Jia-Ju Bai 0 siblings, 0 replies; 3+ messages in thread From: Jia-Ju Bai @ 2021-03-05 7:28 UTC (permalink / raw) To: Coly Li; +Cc: linux-bcache, linux-kernel, kent.overstreet Hi Coly, Thanks a lot for your detailed explanation :) Best wishes, Jia-Ju Bai On 2021/3/5 12:05, Coly Li wrote: > On 3/5/21 10:46 AM, Jia-Ju Bai wrote: >> When bch_bio_alloc_pages() fails, no error return code of >> cached_dev_cache_miss() is assigned. >> To fix this bug, ret is assigned with -ENOMEN as error return code. >> >> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn> >> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> >> --- >> drivers/md/bcache/request.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c >> index 29c231758293..9ecaf26c8d60 100644 >> --- a/drivers/md/bcache/request.c >> +++ b/drivers/md/bcache/request.c >> @@ -930,8 +930,10 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s, >> cache_bio->bi_private = &s->cl; >> >> bch_bio_map(cache_bio, NULL); >> - if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) >> + if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO)) { >> + ret = -ENOMEM; >> goto out_put; >> + } >> >> if (reada) >> bch_mark_cache_readahead(s->iop.c, s->d); >> > Thanks for looking at bcache :-) > > Without the above change, -EINTR will be returned. -EINTR is special in > bache's btree iteration code. See bcache_btree_root() from bcache.h, > > 347 #define bcache_btree_root(fn, c, op, ...) \ > 348 ({ \ > 349 int _r = -EINTR; \ > 350 do { \ > 351 struct btree *_b = (c)->root; \ > 352 bool _w = insert_lock(op, _b); \ > 353 rw_lock(_w, _b, _b->level); \ > 354 if (_b == (c)->root && \ > 355 _w == insert_lock(op, _b)) { \ > 356 _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \ > 357 } \ > 358 rw_unlock(_w, _b); \ > 359 bch_cannibalize_unlock(c); \ > 360 if (_r == -EINTR) \ > 361 \ > 362 } while (_r == -EINTR); \ > 363 \ > 364 finish_wait(&(c)->btree_cache_wait, &(op)->wait); \ > 365 _r; \ > 366 }) > > cached_dev_cache_miss() is called by the following code path, > > cache_lookup() ==> bch_btree_map_keys() ==> bcache_btree_root() ==> > bch_btree_map_keys_recurse() ==> cache_lookup_fn() > > Therefore the return value of cached_dev_cache_miss() will be returned > from where s->d->cache_miss() is called from cache_lookup_fn(). And in > macro bcache_btree_root() this return value will be checked. If the > return value is -EINTR, then the whole iteration will be re-do again. > > Returning -ENOMEM works but if the memory allocation failed, there is no > chance to re-do the cache lookup again from bcache_btree_root(). When > system memory is in heavy usage, we want the lookup to try more times > (because GFP_NOIO is set), which is much better then returning -EIO > immediately to caller. > > Therefore NOT setting ret to -ENOMEM in the patching location should be > an on-purpose coding, IMHO. > > Thanks. > > Coly Li > ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-03-05 7:28 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-03-05 2:46 [PATCH] md: bcache: fix error return code of cached_dev_cache_miss() Jia-Ju Bai 2021-03-05 4:05 ` Coly Li 2021-03-05 7:28 ` Jia-Ju Bai
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).