On 18.04.19 г. 9:28 ч., Qu Wenruo wrote: > [BUG] > With kmalloc failure injection for submit_one_bio(), btrfs can crash like: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000038 > #PF error: [WRITE] > PGD 0 P4D 0 > Oops: 0002 [#1] PREEMPT SMP PTI > CPU: 1 PID: 247 Comm: kworker/u8:4 Not tainted 5.1.0-rc5-custom+ #19 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 > Workqueue: writeback wb_workfn (flush-btrfs-6) > RIP: 0010:alloc_btrfs_bio+0x1e/0x30 [btrfs] > Code: 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 0f 1f 44 00 00 48 63 f6 48 63 ff 48 8d 7c fe 18 be 40 8d 00 00 48 c1 e7 02 e8 a2 86 94 e0 <c7> 40 38 00 00 00 00 c7 00 01 00 00 00 c3 0f 1f 40 00 0f 1f 44 00 > Call Trace: > __btrfs_map_block+0x5ce/0x1210 [btrfs] > ? btrfs_bio_counter_inc_blocked+0x3a/0xc0 [btrfs] > btrfs_map_bio+0x9a/0x430 [btrfs] > btree_submit_bio_hook+0x82/0xb0 [btrfs] > submit_one_bio+0x95/0xc0 [btrfs] > copy_oldmem_page_encrypted+0x20/0x20 > ? write_one_eb+0x18f/0x2a0 [btrfs] > ? end_extent_buffer_writeback+0x20/0x20 [btrfs] > ? btree_write_cache_pages+0x12c/0x350 [btrfs] > ? do_writepages+0x41/0xd0 > ? __writeback_single_inode+0x54/0x650 > ? writeback_sb_inodes+0x1f9/0x540 > ? __writeback_inodes_wb+0x5d/0xb0 > ? wb_writeback+0x340/0x4b0 > ? wb_workfn+0x410/0x5d0 > ? process_one_work+0x294/0x650 > ? worker_thread+0x2d/0x3d0 > ? process_one_work+0x650/0x650 > ? kthread+0x112/0x130 > ? kthread_park+0x80/0x80 > ? ret_from_fork+0x3a/0x50 > ---[ end trace b637169fb8b17c9c ]--- > > [CAUSE] > We just forgot to check the return value of kmalloc. > Surprisingly, all alloc_btrfs_bio() callers have handled memory > allocation pretty well. > The allocation uses the GFP_NOFAIL modified, which, according to the docs: * The VM implementation _must_ retry infinitely: the caller * cannot handle allocation failures. The allocation could block * indefinitely but will never return with failure. Testing for * failure is pointless. The allocation requested is at least 128 bytes (assuming real_stripes is 0). 96 + 24 * total_stripes + 4 * real_stripes + 8 * total_stripes Considering this I think it might be prudent to also remove the NOFAIL flag altogether > [FIX] > Check and return if we failed memory allocation. > > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> Though the change is fine: Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx> > --- > fs/btrfs/volumes.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 78bab7803bda..875d0eee1785 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -5582,6 +5582,8 @@ static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes) > sizeof(u64) * (total_stripes), > GFP_NOFS|__GFP_NOFAIL); > > + if (!bbio) > + return NULL; > atomic_set(&bbio->error, 0); > refcount_set(&bbio->refs, 1); > >
