From 2e6e518335f81d651021a8873da1c938ca0bf1fc Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Tue, 12 May 2015 00:28:11 +0100 Subject: [PATCH] Btrfs: fix block group ->space_info null pointer dereference When we create a block group we add it to the rbtree of block groups before setting its ->space_info field (while it's NULL). This is problematic since other tasks can access the block group from the rbtree and attempt to use its ->space_info before it is set by btrfs_make_block_group(). This can happen for example when a concurrent fitrim ioctl operation is ongoing, which produces a trace like the following when CONFIG_DEBUG_PAGEALLOC is set. [11509.604369] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 [11509.606373] IP: [] __lock_acquire+0xb4/0xf02 [11509.608179] PGD 2296a8067 PUD 22f4a2067 PMD 0 [11509.608179] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [11509.608179] Modules linked in: btrfs crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse acpi_cpufreq processor i2c_piix4 psmou [11509.608179] CPU: 10 PID: 8538 Comm: fstrim Tainted: G W 4.0.0-rc5-btrfs-next-9+ #2 [11509.608179] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [11509.608179] task: ffff88009f5c46d0 ti: ffff8801b3edc000 task.ti: ffff8801b3edc000 [11509.608179] RIP: 0010:[] [] __lock_acquire+0xb4/0xf02 [11509.608179] RSP: 0018:ffff8801b3edf9e8 EFLAGS: 00010002 [11509.608179] RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000000000000 [11509.608179] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000018 [11509.608179] RBP: ffff8801b3edfaa8 R08: 0000000000000001 R09: 0000000000000000 [11509.608179] R10: 0000000000000000 R11: ffff88009f5c4f98 R12: 0000000000000000 [11509.608179] R13: 0000000000000000 R14: 0000000000000018 R15: ffff88009f5c46d0 [11509.608179] FS: 00007f280a10e840(0000) GS:ffff88023ed40000(0000) knlGS:0000000000000000 [11509.608179] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [11509.608179] CR2: 0000000000000018 CR3: 00000002119bc000 CR4: 00000000000006e0 [11509.608179] Stack: [11509.608179] 0000000000000000 0000000000000000 0000000000000004 0000000000000000 [11509.608179] ffff880100000000 ffffffff00000000 0000000000000001 ffffffff00000000 [11509.608179] 0000000000000001 0000000000000000 ffff880100000000 00000000000006c4 [11509.608179] Call Trace: [11509.608179] [] ? __lock_acquire+0x696/0xf02 [11509.608179] [] lock_acquire+0xa5/0x116 [11509.608179] [] ? do_trimming+0x51/0x145 [btrfs] [11509.608179] [] _raw_spin_lock+0x34/0x44 [11509.608179] [] ? do_trimming+0x51/0x145 [btrfs] [11509.608179] [] do_trimming+0x51/0x145 [btrfs] [11509.608179] [] btrfs_trim_block_group+0x201/0x491 [btrfs] [11509.608179] [] btrfs_trim_fs+0xe0/0x129 [btrfs] [11509.608179] [] btrfs_ioctl_fitrim+0x138/0x167 [btrfs] [11509.608179] [] btrfs_ioctl+0x50d/0x21e8 [btrfs] [11509.608179] [] ? might_fault+0x58/0xb5 [11509.608179] [] ? might_fault+0x58/0xb5 [11509.608179] [] ? might_fault+0x58/0xb5 [11509.608179] [] ? cp_new_stat+0x147/0x15e [11509.608179] [] do_vfs_ioctl+0x3c6/0x479 [11509.608179] [] ? SYSC_newfstat+0x25/0x2e [11509.608179] [] ? ret_from_sys_call+0x1d/0x58 [11509.608179] [] ? __fget_light+0x2d/0x4f [11509.608179] [] SyS_ioctl+0x5a/0x7f [11509.608179] [] system_call_fastpath+0x12/0x17 [11509.608179] Code: f4 01 00 0f 85 c0 00 00 00 48 c7 c1 f3 1f 7d 81 48 c7 c2 aa cb 7c 81 be fc 0b 00 00 eb 70 83 3d 61 eb 9c 00 00 0f 84 a5 00 00 00 <49> 81 3e 40 a3 2b 82 b8 00 00 00 [11509.608179] RIP [] __lock_acquire+0xb4/0xf02 [11509.608179] RSP [11509.608179] CR2: 0000000000000018 [11509.608179] ---[ end trace 570a5c6769f0e49a ]--- Which corresponds to the following access in fs/btrfs/free-space-cache.c: static int do_trimming(struct btrfs_block_group_cache *block_group, u64 *total_trimmed, u64 start, u64 bytes, u64 reserved_start, u64 reserved_bytes, struct btrfs_trim_range *trim_entry) { struct btrfs_space_info *space_info = block_group->space_info; (...) spin_lock(&space_info->lock); ^^^^^ - block_group->space_info is NULL... Fix this by ensuring the block group's ->space_info is set before adding the block group to the rbtree. Signed-off-by: Filipe Manana Signed-off-by: Chris Mason --- fs/btrfs/extent-tree.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 0ec3acd14cbf..1cbc71d8cb96 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -3693,7 +3693,8 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags, found->disk_total += total_bytes * factor; found->bytes_used += bytes_used; found->disk_used += bytes_used * factor; - found->full = 0; + if (total_bytes > 0) + found->full = 0; spin_unlock(&found->lock); *space_info = found; return 0; @@ -3721,7 +3722,10 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags, found->bytes_reserved = 0; found->bytes_readonly = 0; found->bytes_may_use = 0; - found->full = 0; + if (total_bytes > 0) + found->full = 0; + else + found->full = 1; found->force_alloc = CHUNK_ALLOC_NO_FORCE; found->chunk_alloc = 0; found->flush = 0; @@ -9562,6 +9566,19 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, free_excluded_extents(root, cache); + /* + * Call to ensure the corresponding space_info object is created and + * assigned to our block group, but don't update its counters just yet. + * We want our bg to be added to the rbtree with its ->space_info set. + */ + ret = update_space_info(root->fs_info, cache->flags, 0, 0, + &cache->space_info); + if (ret) { + btrfs_remove_free_space_cache(cache); + btrfs_put_block_group(cache); + return ret; + } + ret = btrfs_add_block_group_cache(root->fs_info, cache); if (ret) { btrfs_remove_free_space_cache(cache); @@ -9569,6 +9586,10 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, return ret; } + /* + * Now that our block group has its ->space_info set and is inserted in + * the rbtree, update the space info's counters. + */ ret = update_space_info(root->fs_info, cache->flags, size, bytes_used, &cache->space_info); if (ret) { -- 2.30.2