diff options
| author | Yuwen Chen <ywen.chen@foxmail.com> | 2025-11-19 12:13:45 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-11-24 15:08:55 -0800 |
| commit | 04d31610a7221cca624646241b1f6b3edd6c99fd (patch) | |
| tree | 15b0c13cc6734c774bed50c701a30c2b93f19f37 | |
| parent | ecf371b2cabee6a2bfb61f87d71c9f02a9ff34d7 (diff) | |
zram: fix the issue that the write - back limits might overflow
When the page size exceeds 4KB, if bd_wb_limit is set to a value that is
not aligned with the page size, it will cause a numerical wrap-around
issue for bd_wb_limit. For example, when the page size is set to 16KB and
bd_wb_limit is set to 3, after one write-back operation, the value of
bd_wb_limit will become -1. More seriously, since bd_wb_limit is an
unsigned number, its value may become as large as 2^64 - 1.
The core reason for this problem is that the unit of bd_wb_limit is 4KB.
For example, when a write-back occurs on a system with a page size of
16KB, 4 needs to be subtracted from bd_wb_limit. This operation takes
place in the zram_account_writeback_submit function.
This patch fixes the issue by limiting bd_wb_limit to be an integer
multiple of PAGE_SIZE / 4096.
Link: https://lkml.kernel.org/r/tencent_5936CFE72BAB2BA76887BB69DCC1B5E67C05@qq.com
Fixes: 1d69a3f8ae77 ("zram: idle writeback fixes and cleanup")
Signed-off-by: Yuwen Chen <ywen.chen@foxmail.com>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Richard Chang <richardycc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | drivers/block/zram/zram_drv.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 3428f647d0a7..1a1159a70fb4 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -566,6 +566,16 @@ static ssize_t writeback_limit_store(struct device *dev, if (kstrtoull(buf, 10, &val)) return ret; + /* + * When the page size is greater than 4KB, if bd_wb_limit is set to + * a value that is not page - size aligned, it will cause value + * wrapping. For example, when the page size is set to 16KB and + * bd_wb_limit is set to 3, a single write - back operation will + * cause bd_wb_limit to become -1. Even more terrifying is that + * bd_wb_limit is an unsigned number. + */ + val = rounddown(val, PAGE_SIZE / 4096); + down_write(&zram->init_lock); zram->bd_wb_limit = val; up_write(&zram->init_lock); |