'Murphy Zhou' reports[1] hitting the panic when running xfstests generic/108 on pmem ramdisk. In his words: This test is simulating partial disk error when calling fsync(): create a lvm vg which consists of 2 disks: one scsi_debug disk; one other disk I specified, pmem ramdisk in this case. create lv in this vg and write to it, make sure writing across 2 disks; offline scsi_debug disk; write again to allocated area; expect fsync: IO error. If one of the disks is pmem ramdisk, it reproduces every time on my setup, on v5.3-rc2+. The mount -o dax option is not required to reproduce this panic. ... Fix this by returning false from 'device_synchronous' function when dax_dev is NULL. [ 1984.878208] BUG: kernel NULL pointer dereference, address: 00000000000002d0 [ 1984.882546] #PF: supervisor read access in kernel mode [ 1984.885664] #PF: error_code(0x0000) - not-present page [ 1984.888626] PGD 0 P4D 0 [ 1984.890140] Oops: 0000 [#1] SMP PTI ... ... [ 1984.943682] Call Trace: [ 1984.945007] device_synchronous+0xe/0x20 [dm_mod] [ 1984.947328] stripe_iterate_devices+0x48/0x60 [dm_mod] [ 1984.949947] ? dm_set_device_limits+0x130/0x130 [dm_mod] [ 1984.952516] dm_table_supports_dax+0x39/0x90 [dm_mod] [ 1984.954989] dm_table_set_restrictions+0x248/0x5d0 [dm_mod] [ 1984.957685] dm_setup_md_queue+0x66/0x110 [dm_mod] [ 1984.960280] table_load+0x1e3/0x390 [dm_mod] [ 1984.962491] ? retrieve_status+0x1c0/0x1c0 [dm_mod] [ 1984.964910] ctl_ioctl+0x1d3/0x550 [dm_mod] [ 1984.967006] ? path_lookupat+0xf4/0x200 [ 1984.968890] dm_ctl_ioctl+0xa/0x10 [dm_mod] [ 1984.970920] do_vfs_ioctl+0xa9/0x630 [ 1984.972701] ksys_ioctl+0x60/0x90 [ 1984.974335] __x64_sys_ioctl+0x16/0x20 [ 1984.976221] do_syscall_64+0x5b/0x1d0 [ 1984.978091] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [1] https://lore.kernel.org/linux-fsdevel/2011806368.5335560.1564469373050.JavaMail.zimbra@xxxxxxxxxx/T/#mac662eb50b9d7bd282b23e6e8625a3f7a4687506 Fixes: 2e9ee0955d3c ("dm: enable synchronous dax") Reported-by: jencce.kernel@xxxxxxxxx Tested-by: jencce.kernel@xxxxxxxxx Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx> --- drivers/md/dm-table.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c index caaee8032afe..b065845c1bdd 100644 --- a/drivers/md/dm-table.c +++ b/drivers/md/dm-table.c @@ -894,6 +894,9 @@ int device_supports_dax(struct dm_target *ti, struct dm_dev *dev, static int device_synchronous(struct dm_target *ti, struct dm_dev *dev, sector_t start, sector_t len, void *data) { + if (!dev->dax_dev) + return false; + return dax_synchronous(dev->dax_dev); } -- 2.20.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
