From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f50.google.com (mail-ed1-f50.google.com [209.85.208.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AA9D04BCABA for ; Mon, 28 Sep 2026 16:49:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790614168; cv=none; b=bixTxqoTpIW2L9/HW1DkwpdNYU0LliG4Ob+63VcuKO+ildlxP7K1Pd20KvlT/VuGSPkI8NQVkCqh+Jb8mrVYzamyqY+A7QLcRCDbtax6/8kZ1a2z/ak/SZyep8yzJNq8yXRna3y0pI677VIVJBQSurx1P24cAF9QzYQ0YRfnsAo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790614168; c=relaxed/simple; bh=bp+qWhqWaR9Lz830v75yldw0X9URi4cGTw7lByuKNn0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gSyFWVuK21uyi0nNxQ8G4JkIkdEcvsNcpqbiOcnFt/ZNcAA09mUpT8lVYgow1wophtv3H/utZvSBKSxuKJ6f5i2WY/GN4FQ8R8ki4psN5XIlW41EguTw7ve3VH5cSW3cYhKE9na+eTXxFrh7vCGxmUmXkfv5oHSsFA9x0dOtVG4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=HfKPSmhL; arc=none smtp.client-ip=209.85.208.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="HfKPSmhL" Received: by mail-ed1-f50.google.com with SMTP id 4fb4d7f45d1cf-6aaf28a86b9so72610a12.1 for ; Mon, 28 Sep 2026 09:49:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1790614165; x=1791218965; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=xejTefUm/OK3UUWyW9Ph3jbUHFaoxjGvqLJqChvouko=; b=HfKPSmhL1mSfI/omSQRd3bzq9EcoUjfM0sq964iCCu4bnn3RktFWcxWd9DP0ru0yhK kcXGxY1m7TX8z3oMnS/YdM5QSMC6OXuJj2EsZXIQtXo+SngOQ6lP5PT0EQwtAh3CLO6+ 7oMxOPqnvOG4dfb9JBUpJinWnuepar3GEH4EcRZdLyvqiCYpcnOGS90pvb+emSBO8dg/ T8h5gxwQaWZWzQP2bSeW7sYkMML9BqQI15uwuZv18lQf5SQngSqP/WmGga9TsLe25Fm+ 0V8WvYZ+iGa7bmH7vtv0gSQCjYQW+vA4I725Kz4L6l/fSzBcJZ/CJ0kbMgVukTzR4W0V yk6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790614165; x=1791218965; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=xejTefUm/OK3UUWyW9Ph3jbUHFaoxjGvqLJqChvouko=; b=VBM2pseKujR4e/oDveY9F7VBU5i1A3JpZPk55OK41J0fGSL3dwZJ8+3fl8aADJvyhu sEqVOnXQNFhZbkYy9dH/x24vvawlrM+tUUbDuVQYyZyg56Pz2HxGO59CqWipv1WOjbXw MymOQjXiAUw66/TStc1Ao4ERPlaf+QvI3mtDWbCacepwmHwODdaV+3YeNtA+i+9NRCGN GH3vTazz4KskgcL9qnnar5swhjiUboO/J4RMZPqQHugi7TSKevh5ewM8gy92ljBU3o93 9VY0ymKBDGCdGl4J/yPriyobs/RqYP2tpTxS8tnAI+tM8zB4/ex8zwkDzoQ1TOglEjRu hnLg== X-Forwarded-Encrypted: i=1; AKwUvByHqZlPOw2MnbxXwnR+gcfXgrUGcyEwO9Bg/EXiSP1Ft2SjVfDr7RpH3Y9JC1WgriHJaRCIN+fSVFhPdcs=@vger.kernel.org X-Gm-Message-State: AFq9FYKtBXr/V5iyXNRZiGxdzQHxP1nRXWLVNdnIpcU3k1d+/oKyUlCv tLDAHr00/2GaTKnkRAYyYuOhwRmjDIhOfAQFMwR4YPfGVZHzQv0H7CU1 X-Gm-Gg: AYBFou3EznJoyqHKBg+AUHW63JM2Y3HnSZVECA90jGLMBl9NoG8ahpzuYYilp4eyQbJ fBMF1vBd7AMZd631xyPpjFeeNQTKtghSWTaIbRjdcZWJtNU4jteDkwNfOgf99Luna7yNHaYBTEb TWDdH0SrxXMhbdnuRm5RQCLUoeUSD0etslsq1XQQOjE6ID7mg0FDHy976onwFRMZxqM834DSF1N /tU3NXO1iLii1wnvewBVw+pNEO7JWCOHBtfKkbWdYAvf1GuhJgMJ2Y10dF1QngXZxPx4Q0/S4Kv iuj0UY9BodXjJZ7DjENPY7xUFM93wF7UfoElFgNbdiak142rv1pTzHyOor3KWrUgcQxlkR5YIOr qpndbzahe7sL3fbfECiHCBE0QHbyASaWovfS/sby7xT51G2l/z3x4nIpSLqNxgyH/i6IPJwRDAd LHh69gYxc49Wlu2kMQLaE6KyoMxL/gx7QAsOud6flMu7rWwm4inS+8oaCV2yVA/kkwTDdJmrVWr ztBoSR1G35wIRFg38PECBT8b8SwX7H9n8P2k34Hc4mH8mT9cktjU/69DQeQZZ89RShw0J0ROntl EhRDOGLWXOk= X-Received: by 2002:aa7:d1c8:0:b0:6aa:f83e:1da7 with SMTP id 4fb4d7f45d1cf-6aaf83e1fedmr5025670a12.0.1790614164665; Mon, 28 Sep 2026 09:49:24 -0700 (PDT) Received: from localhost.localdomain (84-216-182-59.customers.ownit.se. [84.216.182.59]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6ab5be57b13sm3066998a12.33.2026.09.28.09.49.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Sep 2026 09:49:24 -0700 (PDT) From: Pooyan Azad To: Minchan Kim , Sergey Senozhatsky Cc: Andrew Morton , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] zram: fix short reads from block_state Date: Mon, 28 Sep 2026 18:48:26 +0200 Message-ID: <20260928164826.24858-1-pooyan.azadparvar@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 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. Fixes: c0265342bff4 ("zram: introduce zram memory tracking") Closes: https://lore.kernel.org/r/CANC3H+LdtoydSp+o2ecErAw7k6R2+gRf9LyxcaoHv_mGhJmyQQ@mail.gmail.com/ Signed-off-by: Pooyan Azad --- Compile-tested with: make O=/tmp/zram-build W=1 -j$(nproc) \ drivers/block/zram/zram_drv.o No runtime testing of the patched kernel was performed. drivers/block/zram/zram_drv.c | 101 ++++++++++++++++++---------------- 1 file changed, 53 insertions(+), 48 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index a9b3bb1d3bef..66a2fdb1274b 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1542,68 +1542,73 @@ 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; + return &zram->table[*pos]; +} - slot_lock(zram, index); - if (!slot_allocated(zram, index)) - goto next; +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; - 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: + ++*pos; + if (*pos >= nr_pages) + return NULL; + + return &zram->table[*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; + struct zram_table_entry *entry = v; + unsigned long index = entry - zram->table; + + slot_lock(zram, index); + if (!slot_allocated(zram, index)) { slot_unlock(zram, index); - *ppos += 1; + return SEQ_SKIP; } - if (copy_to_user(buf, kbuf, written)) - written = -EFAULT; - kvfree(kbuf); + 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 written; + return 0; } -static const struct file_operations proc_zram_block_state_op = { - .open = simple_open, - .read = read_block_state, - .llseek = default_llseek, +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) { @@ -1613,7 +1618,7 @@ 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) -- 2.43.0