| Message ID | 20231019194924.100347-1-sj@kernel.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | avoid divide-by-zero due to max_nr_accesses overflow | expand |
On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park <sj@kernel.org> wrote: > The maximum nr_accesses of given DAMON context can be calculated by > dividing the aggregation interval by the sampling interval. Some logics > in DAMON uses the maximum nr_accesses as a divisor. Hence, the value > shouldn't be zero. Such case is avoided since DAMON avoids setting the > agregation interval as samller than the sampling interval. However, > since nr_accesses is unsigned int while the intervals are unsigned long, > the maximum nr_accesses could be zero while casting. Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags for him. I sure Andrew could add that on his own, but I want to minimize Andrew's load, so will send v2 of this patchset. Andrew, please let me know if that doesn't help but only increasing your load. Thanks, SJ > > Avoid the divide-by-zero by implementing a function that handles the > corner case (first patch), and replaces the vulnerable direct max > nr_accesses calculations (remaining patches). > > Note that the patches for the replacements are divided for broken > commits, to make backporting on required tres easier. Especially, the > last patch is for a patch that not yet merged into the mainline but in > mm tree. > > SeongJae Park (5): > mm/damon: implement a function for max nr_accesses safe calculation > mm/damon/core: avoid divide-by-zero during monitoring results update > mm/damon/ops-common: avoid divide-by-zero during region hotness > calculation > mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation > mm/damon/core: avoid divide-by-zero from pseudo-moving window length > calculation > > include/linux/damon.h | 7 +++++++ > mm/damon/core.c | 12 +++--------- > mm/damon/lru_sort.c | 4 +--- > mm/damon/ops-common.c | 5 ++--- > 4 files changed, 13 insertions(+), 15 deletions(-) > > > base-commit: e845524c56a529768a8793e96304db09134eafdf > -- > 2.34.1 > >
On Fri, 20 Oct 2023 17:19:01 +0000 SeongJae Park <sj@kernel.org> wrote: > On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park <sj@kernel.org> wrote: > > > The maximum nr_accesses of given DAMON context can be calculated by > > dividing the aggregation interval by the sampling interval. Some logics > > in DAMON uses the maximum nr_accesses as a divisor. Hence, the value > > shouldn't be zero. Such case is avoided since DAMON avoids setting the > > agregation interval as samller than the sampling interval. However, > > since nr_accesses is unsigned int while the intervals are unsigned long, > > the maximum nr_accesses could be zero while casting. > > Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags > for him. I sure Andrew could add that on his own, but I want to minimize > Andrew's load, so will send v2 of this patchset. Andrew, please let me know if > that doesn't help but only increasing your load. Editing the changelogs is far quicker than updating a patch series ;) btw, it's now conventional to add a link to the reporter's report. The new "Closes:" tag, immediately after the Reported-by:. But it's not a big deal.
On Fri, 20 Oct 2023 17:19:01 +0000 SeongJae Park <sj@kernel.org> wrote: > On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park <sj@kernel.org> wrote: > > > The maximum nr_accesses of given DAMON context can be calculated by > > dividing the aggregation interval by the sampling interval. Some logics > > in DAMON uses the maximum nr_accesses as a divisor. Hence, the value > > shouldn't be zero. Such case is avoided since DAMON avoids setting the > > agregation interval as samller than the sampling interval. However, > > since nr_accesses is unsigned int while the intervals are unsigned long, > > the maximum nr_accesses could be zero while casting. > > Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags > for him. I sure Andrew could add that on his own, but I want to minimize > Andrew's load, so will send v2 of this patchset. Andrew, please let me know if > that doesn't help but only increasing your load. So sent the second version[1] with the "Reported-by: akub Acs <acsjakub@amazon.de>" line, but then I noticed the patch is already added to mm queue[2]. Somehow the notification mails delivered bit later than usual. Sorry for making this noise, Andrew. Please add "Reported-by: akub Acs <acsjakub@amazon.de>" to already added patches, or replace those with the v2 if possible. Also, please let me know if there's anything I could help. [1] https://lore.kernel.org/damon/20231020172317.64192-1-sj@kernel.org/ [2] https://lore.kernel.org/mm-commits/20231020171847.C6EEAC433C7@smtp.kernel.org/ Thanks, SJ > > > Thanks, > SJ >
On Fri, 20 Oct 2023 10:30:36 -0700 Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 20 Oct 2023 17:19:01 +0000 SeongJae Park <sj@kernel.org> wrote: > > > On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park <sj@kernel.org> wrote: > > > > > The maximum nr_accesses of given DAMON context can be calculated by > > > dividing the aggregation interval by the sampling interval. Some logics > > > in DAMON uses the maximum nr_accesses as a divisor. Hence, the value > > > shouldn't be zero. Such case is avoided since DAMON avoids setting the > > > agregation interval as samller than the sampling interval. However, > > > since nr_accesses is unsigned int while the intervals are unsigned long, > > > the maximum nr_accesses could be zero while casting. > > > > Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags > > for him. I sure Andrew could add that on his own, but I want to minimize > > Andrew's load, so will send v2 of this patchset. Andrew, please let me know if > > that doesn't help but only increasing your load. > > Editing the changelogs is far quicker than updating a patch series ;) > > btw, it's now conventional to add a link to the reporter's report. The > new "Closes:" tag, immediately after the Reported-by:. But it's not a > big deal. Surely it is. And in this case, the report was made privately, so no available link. I should have mentioned this early, sorry. Anyway, thank you for your help, Andrew :) Thanks, SJ
The maximum nr_accesses of given DAMON context can be calculated by dividing the aggregation interval by the sampling interval. Some logics in DAMON uses the maximum nr_accesses as a divisor. Hence, the value shouldn't be zero. Such case is avoided since DAMON avoids setting the agregation interval as samller than the sampling interval. However, since nr_accesses is unsigned int while the intervals are unsigned long, the maximum nr_accesses could be zero while casting. Avoid the divide-by-zero by implementing a function that handles the corner case (first patch), and replaces the vulnerable direct max nr_accesses calculations (remaining patches). Note that the patches for the replacements are divided for broken commits, to make backporting on required tres easier. Especially, the last patch is for a patch that not yet merged into the mainline but in mm tree. SeongJae Park (5): mm/damon: implement a function for max nr_accesses safe calculation mm/damon/core: avoid divide-by-zero during monitoring results update mm/damon/ops-common: avoid divide-by-zero during region hotness calculation mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation mm/damon/core: avoid divide-by-zero from pseudo-moving window length calculation include/linux/damon.h | 7 +++++++ mm/damon/core.c | 12 +++--------- mm/damon/lru_sort.c | 4 +--- mm/damon/ops-common.c | 5 ++--- 4 files changed, 13 insertions(+), 15 deletions(-) base-commit: e845524c56a529768a8793e96304db09134eafdf