On Tue, Jan 31, 2017 at 4:54 AM, Jan Kara <jack@xxxxxxx> wrote: > Currenly blk_get_backing_dev_info() is not safe to be called when the > block device is not open as bdev->bd_disk is NULL in that case. However > inode_to_bdi() uses this function and may be call called from flusher > worker or other writeback related functions without bdev being open > which leads to crashes such as: > > [113031.075540] Unable to handle kernel paging request for data at address 0x00000000 > [113031.075614] Faulting instruction address: 0xc0000000003692e0 > 0:mon> t > [c0000000fb65f900] c00000000036cb6c writeback_sb_inodes+0x30c/0x590 > [c0000000fb65fa10] c00000000036ced4 __writeback_inodes_wb+0xe4/0x150 > [c0000000fb65fa70] c00000000036d33c wb_writeback+0x30c/0x450 > [c0000000fb65fb40] c00000000036e198 wb_workfn+0x268/0x580 > [c0000000fb65fc50] c0000000000f3470 process_one_work+0x1e0/0x590 > [c0000000fb65fce0] c0000000000f38c8 worker_thread+0xa8/0x660 > [c0000000fb65fd80] c0000000000fc4b0 kthread+0x110/0x130 > [c0000000fb65fe30] c0000000000098f0 ret_from_kernel_thread+0x5c/0x6c > --- Exception: 0 at 0000000000000000 > 0:mon> e > cpu 0x0: Vector: 300 (Data Access) at [c0000000fb65f620] > pc: c0000000003692e0: locked_inode_to_wb_and_lock_list+0x50/0x290 > lr: c00000000036cb6c: writeback_sb_inodes+0x30c/0x590 > sp: c0000000fb65f8a0 > msr: 800000010280b033 > dar: 0 > dsisr: 40000000 > current = 0xc0000001d69be400 > paca = 0xc000000003480000 softe: 0 irq_happened: 0x01 > pid = 18689, comm = kworker/u16:10 > > Fix the problem by grabbing reference to bdi on first open of the block > device and drop the reference only once the inode is evicted from > memory. This pins struct backing_dev_info in memory and thus fixes the > crashes. > > Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx> > Reported-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Tested-by: Dan Williams <dan.j.williams@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
