The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 65aa97c4d2bfd76677c211b9d03ef05a98c6d68e Mon Sep 17 00:00:00 2001
From: Christoph Hellwig hch@lst.de Date: Sat, 3 Apr 2021 18:15:29 +0200 Subject: [PATCH] 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
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 @@ -746,6 +746,22 @@ 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;
@@ -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