Skip to content

ARC: Avoid overflows in arc_evict_adj() #17255

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
May 6, 2025
Merged

ARC: Avoid overflows in arc_evict_adj() #17255

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 10 additions & 5 deletions module/zfs/arc.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4225,15 +4225,17 @@ static uint64_t
arc_evict_adj(uint64_t frac, uint64_t total, uint64_t up, uint64_t down,
uint_t balance)
{
if (total < 8 || up + down == 0)
if (total < 32 || up + down == 0)
return (frac);

/*
* We should not have more ghost hits than ghost size, but they
* may get close. Restrict maximum adjustment in that case.
* We should not have more ghost hits than ghost size, but they may
* get close. To avoid overflows below up/down should not be bigger
* than 1/5 of total. But to limit maximum adjustment speed restrict
* it some more.
*/
if (up + down >= total / 4) {
uint64_t scale = (up + down) / (total / 8);
if (up + down >= total / 16) {
uint64_t scale = (up + down) / (total / 32);
up /= scale;
down /= scale;
}
Expand All @@ -4242,6 +4244,7 @@ arc_evict_adj(uint64_t frac, uint64_t total, uint64_t up, uint64_t down,
int s = highbit64(total);
s = MIN(64 - s, 32);

ASSERT3U(frac, <=, 1ULL << 32);
uint64_t ofrac = (1ULL << 32) - frac;

if (frac >= 4 * ofrac)
Expand All @@ -4252,6 +4255,8 @@ arc_evict_adj(uint64_t frac, uint64_t total, uint64_t up, uint64_t down,
down = (down << s) / (total >> (32 - s));
down = down * 100 / balance;

ASSERT3U(up, <=, (1ULL << 32) - frac);
ASSERT3U(down, <=, frac);
return (frac + up - down);
}

Expand Down
Loading