diff options
author | Christoph Hellwig <hch@lst.de> | 2021-04-03 19:15:29 +0300 |
---|---|---|
committer | Song Liu <song@kernel.org> | 2021-04-08 08:41:26 +0300 |
commit | 65aa97c4d2bfd76677c211b9d03ef05a98c6d68e (patch) | |
tree | 8b41eac071ed554997c6a34ce489b1da86b991a6 | |
parent | 8b57251f9a91f5e5a599de7549915d2d226cc3af (diff) | |
download | linux-65aa97c4d2bfd76677c211b9d03ef05a98c6d68e.tar.xz |
md: split mddev_find
Split mddev_find into a simple mddev_find that just finds an existing
mddev by the unit number, and a more complicated mddev_find that deals
with find or allocating a mddev.
This turns out to fix this bug reported by Zhao Heming.
----------------------------- snip ------------------------------
commit d3374825ce57 ("md: make devices disappear when they are no longer
needed.") introduced protection between mddev creating & removing. The
md_open shouldn't create mddev when all_mddevs list doesn't contain
mddev. With currently code logic, there will be very easy to trigger
soft lockup in non-preempt env.
*** env ***
kvm-qemu VM 2C1G with 2 iscsi luns
kernel should be non-preempt
*** script ***
about trigger 1 time with 10 tests
`1 node1="15sp3-mdcluster1"
2 node2="15sp3-mdcluster2"
3
4 mdadm -Ss
5 ssh ${node2} "mdadm -Ss"
6 wipefs -a /dev/sda /dev/sdb
7 mdadm -CR /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sda \
/dev/sdb --assume-clean
8
9 for i in {1..100}; do
10 echo ==== $i ====;
11
12 echo "test ...."
13 ssh ${node2} "mdadm -A /dev/md0 /dev/sda /dev/sdb"
14 sleep 1
15
16 echo "clean ....."
17 ssh ${node2} "mdadm -Ss"
18 done
`
I use mdcluster env to trigger soft lockup, but it isn't mdcluster
speical bug. To stop md array in mdcluster env will do more jobs than
non-cluster array, which will leave enough time/gap to allow kernel to
run md_open.
*** stack ***
`ID: 2831 TASK: ffff8dd7223b5040 CPU: 0 COMMAND: "mdadm"
#0 [ffffa15d00a13b90] __schedule at ffffffffb8f1935f
#1 [ffffa15d00a13ba8] exact_lock at ffffffffb8a4a66d
#2 [ffffa15d00a13bb0] kobj_lookup at ffffffffb8c62fe3
#3 [ffffa15d00a13c28] __blkdev_get at ffffffffb89273b9
#4 [ffffa15d00a13c98] blkdev_get at ffffffffb8927964
#5 [ffffa15d00a13cb0] do_dentry_open at ffffffffb88dc4b4
#6 [ffffa15d00a13ce0] path_openat at ffffffffb88f0ccc
#7 [ffffa15d00a13db8] do_filp_open at ffffffffb88f32bb
#8 [ffffa15d00a13ee0] do_sys_open at ffffffffb88ddc7d
#9 [ffffa15d00a13f38] do_syscall_64 at ffffffffb86053cb ffffffffb900008c
or:
[ 884.226509] mddev_put+0x1c/0xe0 [md_mod]
[ 884.226515] md_open+0x3c/0xe0 [md_mod]
[ 884.226518] __blkdev_get+0x30d/0x710
[ 884.226520] ? bd_acquire+0xd0/0xd0
[ 884.226522] blkdev_get+0x14/0x30
[ 884.226524] do_dentry_open+0x204/0x3a0
[ 884.226531] path_openat+0x2fc/0x1520
[ 884.226534] ? seq_printf+0x4e/0x70
[ 884.226536] do_filp_open+0x9b/0x110
[ 884.226542] ? md_release+0x20/0x20 [md_mod]
[ 884.226543] ? seq_read+0x1d8/0x3e0
[ 884.226545] ? kmem_cache_alloc+0x18a/0x270
[ 884.226547] ? do_sys_open+0x1bd/0x260
[ 884.226548] do_sys_open+0x1bd/0x260
[ 884.226551] do_syscall_64+0x5b/0x1e0
[ 884.226554] entry_SYSCALL_64_after_hwframe+0x44/0xa9
`
*** rootcause ***
"mdadm -A" (or other array assemble commands) will start a daemon "mdadm
--monitor" by default. When "mdadm -Ss" is running, the stop action will
wakeup "mdadm --monitor". The "--monitor" daemon will immediately get
info from /proc/mdstat. This time mddev in kernel still exist, so
/proc/mdstat still show md device, which makes "mdadm --monitor" to open
/dev/md0.
The previously "mdadm -Ss" is removing action, the "mdadm --monitor"
open action will trigger md_open which is creating action. Racing is
happening.
`<thread 1>: "mdadm -Ss"
md_release
mddev_put deletes mddev from all_mddevs
queue_work for mddev_delayed_delete
at this time, "/dev/md0" is still available for opening
<thread 2>: "mdadm --monitor ..."
md_open
+ mddev_find can't find mddev of /dev/md0, and create a new mddev and
| return.
+ trigger "if (mddev->gendisk != bdev->bd_disk)" and return
-ERESTARTSYS.
`
In non-preempt kernel, <thread 2> is occupying on current CPU. and
mddev_delayed_delete which was created in <thread 1> also can't be
schedule.
In preempt kernel, it can also trigger above racing. But kernel doesn't
allow one thread running on a CPU all the time. after <thread 2> running
some time, the later "mdadm -A" (refer above script line 13) will call
md_alloc to alloc a new gendisk for mddev. it will break md_open
statement "if (mddev->gendisk != bdev->bd_disk)" and return 0 to caller,
the soft lockup is broken.
------------------------------ snip ------------------------------
Cc: stable@vger.kernel.org
Fixes: d3374825ce57 ("md: make devices disappear when they are no longer needed.")
Reported-by: Heming Zhao <heming.zhao@suse.com>
Reviewed-by: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Song Liu <song@kernel.org>
-rw-r--r-- | drivers/md/md.c | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c index e10d91122483..3ce5f4e0f431 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -747,6 +747,22 @@ static struct mddev *mddev_find_locked(dev_t unit) static struct mddev *mddev_find(dev_t unit) { + struct mddev *mddev; + + if (MAJOR(unit) != MD_MAJOR) + unit &= ~((1 << MdpMinorShift) - 1); + + spin_lock(&all_mddevs_lock); + mddev = mddev_find_locked(unit); + if (mddev) + mddev_get(mddev); + spin_unlock(&all_mddevs_lock); + + return mddev; +} + +static struct mddev *mddev_find_or_alloc(dev_t unit) +{ struct mddev *mddev, *new = NULL; if (unit && MAJOR(unit) != MD_MAJOR) @@ -5650,7 +5666,7 @@ static int md_alloc(dev_t dev, char *name) * writing to /sys/module/md_mod/parameters/new_array. */ static DEFINE_MUTEX(disks_mutex); - struct mddev *mddev = mddev_find(dev); + struct mddev *mddev = mddev_find_or_alloc(dev); struct gendisk *disk; int partitioned; int shift; @@ -6530,11 +6546,9 @@ static void autorun_devices(int part) md_probe(dev); mddev = mddev_find(dev); - if (!mddev || !mddev->gendisk) { - if (mddev) - mddev_put(mddev); + if (!mddev) break; - } + if (mddev_lock(mddev)) pr_warn("md: %s locked, cannot run\n", mdname(mddev)); else if (mddev->raid_disks || mddev->major_version |