systemd-213: regression with zram

Thanks. I could reproduce.
When I read strace result, fstat access closed fd which seem to be a culprit.

Cced util-linux.

<snip>

open("/dev/zram0", O_RDONLY) = 4
uname({sys="Linux", node="bboxv", ...}) = 0
ioctl(4, BLKGETSIZE64, 0x7fffa2384888) = 0
close(4) = 0
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f8a058ea000 read(4, "# Locale name alias data base.\n#"..., 4096) = 2570

read(4, "", 4096)                       = 0
close(4)                                = 0
munmap(0x7f8a058ea000, 4096)            = 0

open("/usr/share/locale/en_US/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale/en/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale-langpack/en_US/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale-langpack/en/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, "mkswap: ", 8mkswap: ) = 8
write(2, "error: swap area needs to be at "..., 44error: swap area needs to be at least 40 KiB) = 44 write(2, "\n", 1
) = 1
write(2, "\nUsage:\n mkswap [options] device"..., 40
Usage:
mkswap [options] device [size]
) = 40
write(2, "\nOptions:\n -c, --check "..., 479
Options:

 -c, --check               check bad blocks before creating the swap area
 -f, --force               allow swap size area be larger than device
 -p, --pagesize SIZE       specify page size in bytes
 -L, --label LABEL         specify label
 -v, --swapversion NUM     specify swap-space version number
 -U, --uuid UUID           specify the uuid to use
 -V, --version             output version information and exit
 -h, --help                display this help and exit

) = 479
exit_group(1) = ?

But when it was successful, it was as follows via stat("/dev/zram0").

<snip>

open("/dev/zram0", O_RDONLY) = 4
uname({sys="Linux", node="bboxv", ...}) = 0
ioctl(4, BLKGETSIZE64, 0x7fff85926088) = 0
close(4) = 0
stat("/dev/zram0", {st_mode=S_IFBLK|0660, st_rdev=makedev(252, 0), ...}) = 0
open("/dev/zram0", O_RDWR|O_EXCL) = 4
open("/etc/mtab", O_RDONLY|O_CLOEXEC) = 5
fstat(5, {st_mode=S_IFREG|0644, st_size=725, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f984f537000 read(5, "/dev/vda1 / ext4 rw,errors=remou"..., 4096) = 725

read(5, "", 4096)                       = 0
close(5)                                = 0
munmap(0x7f984f537000, 4096)            = 0
ioctl(4, BLKALIGNOFF, 0x7fff85925fcc)   = 0
lseek(4, 0, SEEK_SET)                   = 0
ioctl(4, 0x301, 0x7fff85925fc0)         = -1 ENOTTY (Inappropriate ioctl for device)
fadvise64(4, 0, 0, POSIX_FADV_RANDOM)   = 0
fstat(4, {st_mode=S_IFBLK|0660, st_rdev=makedev(252, 0), ...}) = 0
uname({sys="Linux", node="bboxv", ...}) = 0
ioctl(4, BLKGETSIZE64, 0x15f72b0)       = 0
ioctl(4, CDROM_GET_CAPABILITY, 0)       = -1 ENOTTY (Inappropriate ioctl for device)
lseek(4, 0, SEEK_SET)                   = 0

read(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024
ioctl(4, BLKSSZGET, 0x15f72c8) = 0
lseek(4, 15872, SEEK_SET) = 15872
read(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 512) = 512
lseek(4, 28672, SEEK_SET) = 28672
read(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024
lseek(4, 0, SEEK_SET) = 0
write(4, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 5
fstat(5, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f984f537000 read(5, "# Locale name alias data base.\n#"..., 4096) = 2570

read(5, "", 4096)                       = 0
close(5)                                = 0
munmap(0x7f984f537000, 4096)            = 0

open("/usr/share/locale/en_US/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale/en/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale-langpack/en_US/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) open("/usr/share/locale-langpack/en/LC_MESSAGES/util-linux.mo", O_RDONLY) = -1 ENOENT (No such file or directory) fstat(1, {st_mode=S_IFREG|0644, st_size=8472, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f984f537000
lseek(4, 1024, SEEK_SET) = 1024
write(4, "\1\0\0\0\377\377\0\0\0\0\0\0\205\236:\36b\377N\324\255\224\5\341CH(\376\0\0\0\0"..., 3072) = 3072
fsync(4) = 0
write(1, "Setting up swapspace version 1, "..., 102Setting up swapspace version 1, size = 262140 KiB no label, UUID=859e3a1e-62ff-4ed4-ad94-05e1434828fe
) = 102
exit_group(0) = ?

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When I read disk-utils/mkswap.c, it's not a problem of mkswap. The problem is ioctl(fd, BLKGETSIZE64, bytes) is not work in your scenario. IOW, kernel fault.
Hmm,, will investgate it.

Thanks for the report!
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Hello Alexander,

Could you test this patch? It passed my test.
Thanks!

From: Minchan Kim <[email protected]>
Date: Wed, 25 Jun 2014 09:20:24 +0900
Subject: [PATCH] zram: revalidate disk after capacity change

Alexander reported mkswap on /dev/zram0 is failed if other process is opening the block device file.

Step is as follows,

0. Reset the unused zram device.
1. Use a program that opens /dev/zram0 with O_RDWR and sleeps until killed.
2. While that program sleeps, echo the correct value to /sys/block/zram0/disksize.
3. Verify (e.g. in /proc/partitions) that the disk size is applied correctly. It is.
4. While that program still sleeps, attempt to mkswap /dev/zram0. This fails:
result: mkswap: error: swap area needs to be at least 40 KiB

When I investigated, the size get by ioctl(fd, BLKGETSIZE64) on mkswap to get a size of blockdev was zero although zram0 has right size by 2.

The reason is zram didn't revalidate disk after changing capacity so that size of blockdev's inode is not uptodate until all of file is close.

This patch should fix the problem.

---
 drivers/block/zram/zram_drv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

index 48eccb350180..089e72cd37be 100644
@@ -622,8 +622,10 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
 	zram->disksize = 0;
-	if (reset_capacity)
+	if (reset_capacity) {
 		set_capacity(zram->disk, 0);
+		revalidate_disk(zram->disk);
+	}
 	up_write(&zram->init_lock);
 }
 

@@ -664,6 +666,7 @@ static ssize_t disksize_store(struct device *dev,
 	zram->comp = comp;
 	zram->disksize = disksize;
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+	revalidate_disk(zram->disk);
 	up_write(&zram->init_lock);
 	return len;
 

2.0.0

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It indeed fixes the problem.

Alexander E. Patrakov