Excerpts from Vineeth Pillai's message of March 25, 2019 6:08 pm: > On Sun, Mar 24, 2019 at 11:30 AM Alex Xu (Hello71) <alex_y_xu@xxxxxxxx> wrote: >> >> I get this BUG in 5.1-rc1 sometimes when powering off the machine. I >> suspect my setup erroneously executes two swapoff+cryptsetup close >> operations simultaneously, so a race condition is triggered. >> >> I am using a single swap on a plain dm-crypt device on a MBR partition >> on a SATA drive. >> >> I think the problem is probably related to >> b56a2d8af9147a4efe4011b60d93779c0461ca97, so CCing the related people. >> > Could you please provide more information on this - stack trace, dmesg etc? > Is it easily reproducible? If yes, please detail the steps so that I > can try it inhouse. > > Thanks, > Vineeth > Some info from the BUG entry (I didn't bother to type it all, low-quality image available upon request): BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 #PF error: [normal kernel read fault] PGD 0 P4D 0 Oops: 0000 [#1] SMP CPU: 0 Comm: swapoff Not tainted 5.1.0-rc1+ #2 RIP: 0010:shmem_recalc_inode+0x41/0x90 Call Trace: ? shmem_undo_range ? rb_erase_cached ? set_next_entity ? __inode_wait_for_writeback ? shmem_truncate_range ? shmem_evict_inode ? evict ? shmem_unuse ? try_to_unuse ? swapcache_free_entries ? _cond_resched ? __se_sys_swapoff ? do_syscall_64 ? entry_SYSCALL_64_after_hwframe As I said, it only occurs occasionally on shutdown. I think it is a safe guess that it can only occur when the swap is not empty, but possibly other conditions are necessary, so I will test further.
