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zram: fix short reads from block_state

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read_block_state() formats each entry directly into the buffer supplied by
read().  If the remaining buffer is too small for one complete record,
snprintf() returns the full record length and the function stops without
copying data or advancing the file position.  A read from this debugfs
file which is smaller than a record therefore returns zero at a non-EOF
position and cannot make progress.

Convert block_state to seq_file so formatted records are buffered
independently of the userspace read size.  Keep dev_lock held across each
seq_file iteration and continue to protect individual entries with their
slot locks.

Link: https://lore.kernel.org/20260929071846.24829-1-pooyan.azadparvar@gmail.com
Fixes: c0265342bf ("zram: introduce zram memory tracking")
Signed-off-by: Pooyan Azad <pooyan.azadparvar@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Closes: https://lore.kernel.org/r/CANC3H+LdtoydSp+o2ecErAw7k6R2+gRf9LyxcaoHv_mGhJmyQQ@mail.gmail.com/
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Tested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pooyan Azad 2026-09-29 09:18:46 +02:00 committed by Andrew Morton
parent b3d3ef5b2f
commit 3720122022
1 changed files with 56 additions and 54 deletions
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110
drivers/block/zram/zram_drv.c
View File

@ -1553,68 +1553,70 @@ static void zram_debugfs_destroy(void)
debugfs_remove_recursive(zram_debugfs_root);
}
static ssize_t read_block_state(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
static void *zram_block_state_start(struct seq_file *seq, loff_t *pos)
{
char *kbuf;
unsigned long index;
ssize_t written = 0;
struct zram *zram = file->private_data;
struct zram *zram = seq->private;
unsigned long nr_pages;
kbuf = kvmalloc(count, GFP_KERNEL);
if (!kbuf)
return -ENOMEM;
guard(rwsem_read)(&zram->dev_lock);
if (!init_done(zram)) {
kvfree(kbuf);
return -EINVAL;
}
down_read(&zram->dev_lock);
if (!init_done(zram))
return ERR_PTR(-EINVAL);
nr_pages = zram->disksize >> PAGE_SHIFT;
if (*pos >= nr_pages)
return NULL;
for (index = *ppos; index < nr_pages; index++) {
int copied;
slot_lock(zram, index);
if (!slot_allocated(zram, index))
goto next;
copied = snprintf(kbuf + written, count,
"%12lu %12u.%06d %c%c%c%c%c%c\n",
index, zram->table[index].attr.ac_time, 0,
test_slot_flag(zram, index, ZRAM_SAME) ? 's' : '.',
test_slot_flag(zram, index, ZRAM_WB) ? 'w' : '.',
test_slot_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
test_slot_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
get_slot_comp_priority(zram, index) ? 'r' : '.',
test_slot_flag(zram, index,
ZRAM_INCOMPRESSIBLE) ? 'n' : '.');
if (count <= copied) {
slot_unlock(zram, index);
break;
}
written += copied;
count -= copied;
next:
slot_unlock(zram, index);
*ppos += 1;
}
if (copy_to_user(buf, kbuf, written))
written = -EFAULT;
kvfree(kbuf);
return written;
return pos;
}
static const struct file_operations proc_zram_block_state_op = {
.open = simple_open,
.read = read_block_state,
.llseek = default_llseek,
static void *zram_block_state_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct zram *zram = seq->private;
unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
++*pos;
if (*pos >= nr_pages)
return NULL;
return pos;
}
static void zram_block_state_stop(struct seq_file *seq, void *v)
{
struct zram *zram = seq->private;
up_read(&zram->dev_lock);
}
static int zram_block_state_show(struct seq_file *seq, void *v)
{
struct zram *zram = seq->private;
unsigned long index = *(loff_t *)v;
slot_lock(zram, index);
if (slot_allocated(zram, index)) {
seq_printf(seq, "%12lu %12u.%06d %c%c%c%c%c%c\n",
index, zram->table[index].attr.ac_time, 0,
test_slot_flag(zram, index, ZRAM_SAME) ? 's' : '.',
test_slot_flag(zram, index, ZRAM_WB) ? 'w' : '.',
test_slot_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
test_slot_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
get_slot_comp_priority(zram, index) ? 'r' : '.',
test_slot_flag(zram, index,
ZRAM_INCOMPRESSIBLE) ? 'n' : '.');
}
slot_unlock(zram, index);
return 0;
}
static const struct seq_operations zram_block_state_sops = {
.start = zram_block_state_start,
.next = zram_block_state_next,
.stop = zram_block_state_stop,
.show = zram_block_state_show,
};
DEFINE_SEQ_ATTRIBUTE(zram_block_state);
static void zram_debugfs_register(struct zram *zram)
{
@ -1624,7 +1626,7 @@ static void zram_debugfs_register(struct zram *zram)
zram->debugfs_dir = debugfs_create_dir(zram->disk->disk_name,
zram_debugfs_root);
debugfs_create_file("block_state", 0400, zram->debugfs_dir,
zram, &proc_zram_block_state_op);
zram, &zram_block_state_fops);
}
static void zram_debugfs_unregister(struct zram *zram)