github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

zram: fix idle age_sec underflow in idle_store()

Browse Source 
After commit 2e8ff2f51d ("zram: use u32 for entry ac_time tracking"),
idle_store() computes the idle cutoff as:

	cutoff = ktime_sub((u32)ktime_get_boottime_seconds(), age_sec);

Because the left operand is cast to u32, when age_sec exceeds the current
uptime the subtraction wraps modulo 2^32 and the huge result is
zero-extended into the s64 cutoff.  mark_idle() then marks every entry as
idle instead of matching nothing.  For instance, running

	echo 86400 > /sys/block/zramX/idle

on a machine up for only two minutes marks all newly written pages idle
and hands them to idle writeback and recompression.

No slot can have been accessed before the system booted, so an age_sec
that reaches back past uptime cannot match any slot.  Return early in that
case, without walking the table or taking any slot locks.

Track the cutoff as time64_t rather than ktime_t.  Both cutoff and ac_time
are boot-time values in seconds, so a plain arithmetic comparison against
ac_time in mark_idle() is correct and no ktime helpers are needed.

Link: https://lore.kernel.org/20260828083149.45760-1-jiahao.kernel@gmail.com
Fixes: 2e8ff2f51d ("zram: use u32 for entry ac_time tracking")
Signed-off-by: Hao Jia <jiahao1@lixiang.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Hao Jia 2026-08-28 16:31:49 +08:00 committed by Andrew Morton
parent 0e774fdb2e
commit 59042a88ef
1 changed files with 13 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/block/zram/zram_drv.c
View File

@ -415,7 +415,7 @@ static ssize_t mem_used_max_store(struct device *dev,
* Mark all pages which are older than or equal to cutoff as IDLE.
* Callers should hold the zram init lock in read mode
*/
static void mark_idle(struct zram *zram, ktime_t cutoff)
static void mark_idle(struct zram *zram, time64_t cutoff)
{
int is_idle = 1;
unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
@ -439,7 +439,7 @@ static void mark_idle(struct zram *zram, ktime_t cutoff)
#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
is_idle = !cutoff ||
ktime_after(cutoff, zram->table[index].attr.ac_time);
cutoff > zram->table[index].attr.ac_time;
#endif
if (is_idle)
set_slot_flag(zram, index, ZRAM_IDLE);
@ -453,21 +453,26 @@ static ssize_t idle_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t len)
{
struct zram *zram = dev_to_zram(dev);
ktime_t cutoff = 0;
time64_t cutoff = 0;
if (!sysfs_streq(buf, "all")) {
/*
* If it did not parse as 'all' try to treat it as an integer
* when we have memory tracking enabled.
*/
time64_t uptime;
u32 age_sec;
if (IS_ENABLED(CONFIG_ZRAM_TRACK_ENTRY_ACTIME) &&
!kstrtouint(buf, 0, &age_sec))
cutoff = ktime_sub((u32)ktime_get_boottime_seconds(),
age_sec);
else
if (!IS_ENABLED(CONFIG_ZRAM_TRACK_ENTRY_ACTIME) ||
kstrtouint(buf, 0, &age_sec))
return -EINVAL;
/* No slot can be older than the system uptime */
uptime = ktime_get_boottime_seconds();
if (age_sec >= uptime)
return len;
cutoff = uptime - age_sec;
}
guard(rwsem_read)(&zram->dev_lock);