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mm/page_alloc: only update lowmem_reserve_ratio on sysctl write

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lowmem_reserve_ratio_sysctl_handler() ignores the return value of
proc_dointvec_minmax() and always calls setup_per_zone_lowmem_reserve(),
even for read operations.

Fix three issues:

1. Propagate errors from proc_dointvec_minmax() instead of always
   returning success.  For example, writing non-integer garbage to the
   sysctl now returns an error instead of silently succeeding with
   unchanged values.

2. Only call setup_per_zone_lowmem_reserve() when the sysctl is
   actually written, matching the write-only refresh pattern of
   min_free_kbytes and watermark_scale_factor handlers.

3. On write, parse into a temporary ratio[] array and only copy into
   sysctl_lowmem_reserve_ratio[] and refresh derived state after the
   full vector is validated.  This avoids leaving the ratio array
   partially updated while skipping setup when proc_dointvec_minmax()
   returns an error on a later element (suggested by Andrew Morton).

Drop the manual "< 1 -> 0" sanitization loop and set .extra1 = SYSCTL_ZERO
on the ctl_table entry so proc_dointvec_minmax() enforces the minimum on
write; negative values now return -EINVAL instead of being silently
coerced to 0 (suggested by Vlastimil Babka).

[akpm@linux-foundation.org: add comment, per hannes]
  Link: https://lore.kernel.org/anSRGASe5FIrqwlg@cmpxchg.org
Link: https://lore.kernel.org/linux-mm/tencent_FFD4F4D728AAE8A8AE0AF277A59854A29A06@qq.com/
Link: https://lore.kernel.org/tencent_A860C873956A52E26AD8D309A308A241BA08@qq.com
Signed-off-by: Jianlin Shi <shijianlin11@foxmail.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joel Granados <joel.granados@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jianlin Shi
2026-08-06 16:27:34 +08:00
committed by Andrew Morton
parent c310a8932a
commit 8282cb36d0
1 changed files with 20 additions and 8 deletions
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28
mm/page_alloc.c
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@@ -6853,8 +6853,8 @@ static int sysctl_min_slab_ratio_sysctl_handler(const struct ctl_table *table, i
/*
* lowmem_reserve_ratio_sysctl_handler - just a wrapper around
* proc_dointvec() so that we can call setup_per_zone_lowmem_reserve()
* whenever sysctl_lowmem_reserve_ratio changes.
* proc_dointvec_minmax() so that we can call
* setup_per_zone_lowmem_reserve() when the sysctl is written.
*
* The reserve ratio obviously has absolutely no relation with the
* minimum watermarks. The lowmem reserve ratio can only make sense
@@ -6863,16 +6863,27 @@ static int sysctl_min_slab_ratio_sysctl_handler(const struct ctl_table *table, i
static int lowmem_reserve_ratio_sysctl_handler(const struct ctl_table *table,
int write, void *buffer, size_t *length, loff_t *ppos)
{
int i;
struct ctl_table tmp = *table;
int ratio[ARRAY_SIZE(sysctl_lowmem_reserve_ratio)];
int rc;
proc_dointvec_minmax(table, write, buffer, length, ppos);
if (!write)
return proc_dointvec_minmax(table, write, buffer, length, ppos);
for (i = 0; i < MAX_NR_ZONES; i++) {
if (sysctl_lowmem_reserve_ratio[i] < 1)
sysctl_lowmem_reserve_ratio[i] = 0;
}
/*
* proc_dointvec_max() works incrementally. Use a buffer and only set
* the values if all of them parse cleanly.
*/
memcpy(ratio, sysctl_lowmem_reserve_ratio, sizeof(ratio));
tmp.data = ratio;
rc = proc_dointvec_minmax(&tmp, write, buffer, length, ppos);
if (rc)
return rc;
memcpy(sysctl_lowmem_reserve_ratio, ratio, sizeof(ratio));
setup_per_zone_lowmem_reserve();
return 0;
}
@@ -6971,6 +6982,7 @@ static const struct ctl_table page_alloc_sysctl_table[] = {
.maxlen = sizeof(sysctl_lowmem_reserve_ratio),
.mode = 0644,
.proc_handler = lowmem_reserve_ratio_sysctl_handler,
.extra1 = SYSCTL_ZERO,
},
#ifdef CONFIG_NUMA
{