Btrfs: fix btrfs boot when compiled as built-in

After the change titled "Btrfs: add support for inode properties", if
btrfs was built-in the kernel (i.e. not as a module), it would cause a
kernel panic, as reported recently by Fengguang:

[    2.024722] BUG: unable to handle kernel NULL pointer dereference at           (null)
[    2.027814] IP: [<ffffffff81501594>] crc32c+0xc/0x6b
[    2.028684] PGD 0
[    2.028684] Oops: 0000 [#1] SMP
[    2.028684] Modules linked in:
[    2.028684] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc7-04795-ga7b57c2 #1
[    2.028684] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[    2.028684] task: ffff88000edba100 ti: ffff88000edd6000 task.ti: ffff88000edd6000
[    2.028684] RIP: 0010:[<ffffffff81501594>]  [<ffffffff81501594>] crc32c+0xc/0x6b
[    2.028684] RSP: 0000:ffff88000edd7e58  EFLAGS: 00010246
[    2.028684] RAX: 0000000000000000 RBX: ffffffff82295550 RCX: 0000000000000000
[    2.028684] RDX: 0000000000000011 RSI: ffffffff81efe393 RDI: 00000000fffffffe
[    2.028684] RBP: ffff88000edd7e60 R08: 0000000000000003 R09: 0000000000015d20
[    2.028684] R10: ffffffff81ef225e R11: ffffffff811b0222 R12: ffffffffffffffff
[    2.028684] R13: 0000000000000239 R14: 0000000000000000 R15: 0000000000000000
[    2.028684] FS:  0000000000000000(0000) GS:ffff88000fa00000(0000) knlGS:0000000000000000
[    2.028684] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    2.028684] CR2: 0000000000000000 CR3: 000000000220c000 CR4: 00000000000006f0
[    2.028684] Stack:
[    2.028684]  ffffffff82295550 ffff88000edd7e80 ffffffff8238af62 ffffffff8238ac05
[    2.028684]  0000000000000000 ffff88000edd7e98 ffffffff8238ac0f ffffffff8238ac05
[    2.028684]  ffff88000edd7f08 ffffffff810002ba ffff88000edd7f00 ffffffff810e2404
[    2.028684] Call Trace:
[    2.028684]  [<ffffffff8238af62>] btrfs_props_init+0x4f/0x96
[    2.028684]  [<ffffffff8238ac05>] ? ftrace_define_fields_btrfs_space_reservation+0x145/0x145
[    2.028684]  [<ffffffff8238ac0f>] init_btrfs_fs+0xa/0xf0
[    2.028684]  [<ffffffff8238ac05>] ? ftrace_define_fields_btrfs_space_reservation+0x145/0x145
[    2.028684]  [<ffffffff810002ba>] do_one_initcall+0xa4/0x13a
[    2.028684]  [<ffffffff810e2404>] ? parse_args+0x25f/0x33d
[    2.028684]  [<ffffffff8234cf75>] kernel_init_freeable+0x1aa/0x230
[    2.028684]  [<ffffffff8234c785>] ? do_early_param+0x88/0x88
[    2.028684]  [<ffffffff819f61b5>] ? rest_init+0x89/0x89
[    2.028684]  [<ffffffff819f61c3>] kernel_init+0xe/0x109

The issue here is that the initialization function of btrfs (super.c:init_btrfs_fs)
started using crc32c (from lib/libcrc32c.c). But when it needs to call crc32c (as
part of the properties initialization routine), the libcrc32c is not yet initialized,
so crc32c derreferenced a NULL pointer (lib/libcrc32c.c:tfm), causing the kernel
panic on boot.

The approach to fix this is to use crypto component directly to use its crc32c (which
is basically what lib/libcrc32c.c is, a wrapper around crypto). This is what ext4 is
doing as well, it uses crypto directly to get crc32c functionality.

Verified this works both when btrfs is built-in and when it's loadable kernel module.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/fs/btrfs/hash.c b/fs/btrfs/hash.c
new file mode 100644
index 000000000000..85889aa82c62
--- /dev/null
+++ b/fs/btrfs/hash.c
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2014 Filipe David Borba Manana <fdmanana@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <crypto/hash.h>
+#include <linux/err.h>
+#include "hash.h"
+
+static struct crypto_shash *tfm;
+
+int __init btrfs_hash_init(void)
+{
+        tfm = crypto_alloc_shash("crc32c", 0, 0);
+        if (IS_ERR(tfm))
+                return PTR_ERR(tfm);
+
+        return 0;
+}
+
+void btrfs_hash_exit(void)
+{
+        crypto_free_shash(tfm);
+}
+
+u32 btrfs_crc32c(u32 crc, const void *address, unsigned int length)
+{
+        struct {
+                struct shash_desc shash;
+                char ctx[crypto_shash_descsize(tfm)];
+        } desc;
+        int err;
+
+        desc.shash.tfm = tfm;
+        desc.shash.flags = 0;
+        *(u32 *)desc.ctx = crc;
+
+        err = crypto_shash_update(&desc.shash, address, length);
+        BUG_ON(err);
+
+        return *(u32 *)desc.ctx;
+}