mm/page_alloc: only update lowmem_reserve_ratio on sysctl write

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>

0 files changed, 0 insertions, 0 deletions