On 2023/11/30 23:37, Jens Axboe wrote:
On 11/30/23 8:20 AM, Dongyun Liu wrote:
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d77d3664ca08..ee6c22c50e09 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -514,7 +514,7 @@ static ssize_t backing_dev_store(struct device *dev,
nr_pages = i_size_read(inode) >> PAGE_SHIFT;
bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
- bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
+ bitmap = kmalloc(bitmap_sz, GFP_ATOMIC);
if (!bitmap) {
err = -ENOMEM;
goto out;
Outside of this moving from a zeroed alloc to one that does not, the
change looks woefully incomplete. Why does this allocation need to be
GFP_ATOMIC, and:
By using GFP_ATOMIC, it indicates that the caller cannot reclaim or
sleep, although we can prevent the risk of deadlock when acquiring the
zram->lock again in zram_bvec_write.
1) file_name = kmalloc(PATH_MAX, GFP_KERNEL); does not
There is no zram->init_lock held here, so there is no need to use
GFP_ATOMIC.
2) filp_open() -> getname_kernel() -> __getname() does not
3) filp_open() -> getname_kernel() does not
4) bdev_open_by_dev() does not
Missing the use of GFP_ATOMIC.
IOW, you have a slew of GFP_KERNEL allocations in there, and you
probably just patched the largest one. But the core issue remains.
The whole handling of backing_dev_store() looks pretty broken.
Indeed, this patch only solves the biggest problem and does not
fundamentally solve it, because there are many processes for holding
zram->init_lock before allocation memory in backing_dev_store that need
to be fully modified, and I did not consider it thoroughly. Obviously,
a larger and better patch is needed to eliminate this risk, but it is
currently not necessary.
Thank you for your kind and patient.
