On Thu, Jan 30, 2014 at 3:11 AM, Darrick J. Wong
<darrick.wong@xxxxxxxxxx> wrote:
> On Sun, Jan 12, 2014 at 02:22:46AM +0000, Filipe David Borba Manana wrote:
>> 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.
>
> Sorry, I didn't even see this until your other patch today...
>
> Yes, ext4 bypasses libcrc32c, but notice how ext4/jbd2 only call
> crypto_alloc_shash() when you mount the filesystem. This silly trick enables
> ext4 to take advantage of faster crc32c implementations that don't get loaded
> until after the initial insmod, just in case you do this:
>
> # modprobe btrfs
> # mount /dev/X / <-- / uses software crc32c implementation
> # modprobe crc32c-intel
> # mount /dev/Y /home <-- /home still uses software crc32c, because
> *tfm still points to the sw implementation!
>
> Of course, one could argue that this is a distro problem, and that the
> initramfs or kernel config should take care to load the appropriate hardware
> accelerated drivers /before/ btrfs.
>
> On the other hand, btrfs might as well always enjoy the fastest implementation
> that it can get its hands on.
Thanks Darrick, that's very useful information.
So, if I understood it correctly, before this change btrfs was using
libcrc32c, which is initialized only once and therefore it's possible
it wouldn't use crc32c-intel - if crc32c-intel was built as a module
and not loaded before libcrc32c is initialized.
Also that ext4 approach, of using crypto_alloc_shash() on each mount
(and make the result accessible via super block structure) doesn't
solve the case where the partition is mounted before crc32c-intel is
loaded but then it's never unmounted and mounted again (like a root or
home partition). By solve I mean not profiting from intel's hardware
based crc32c.
I suppose that if crc32c-intel is built-in (i.e. not as a module) that
either with the current approach (after this patch) or with the old
approach, we'll be using crc32c-intel. Is there any way to verify
this?
>
> (Also I suppose metadata_csum is optional in ext4/jbd2...)
>
> --D
>
>>
>> Verified this works both when btrfs is built-in and when it's loadable kernel module.
>>
>> Signed-off-by: Filipe David Borba Manana <fdmanana@xxxxxxxxx>
>> ---
>>
>> V2: Removed unnecessary __exit qualifier.
>>
>> fs/btrfs/Kconfig | 3 ++-
>> fs/btrfs/Makefile | 2 +-
>> fs/btrfs/extent-tree.c | 6 +++---
>> fs/btrfs/hash.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
>> fs/btrfs/hash.h | 11 ++++++++---
>> fs/btrfs/super.c | 10 +++++++++-
>> 6 files changed, 72 insertions(+), 9 deletions(-)
>> create mode 100644 fs/btrfs/hash.c
>>
>> diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
>> index aa976ec..a66768e 100644
>> --- a/fs/btrfs/Kconfig
>> +++ b/fs/btrfs/Kconfig
>> @@ -1,6 +1,7 @@
>> config BTRFS_FS
>> tristate "Btrfs filesystem support"
>> - select LIBCRC32C
>> + select CRYPTO
>> + select CRYPTO_CRC32C
>> select ZLIB_INFLATE
>> select ZLIB_DEFLATE
>> select LZO_COMPRESS
>> diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
>> index af7f000..f341a98 100644
>> --- a/fs/btrfs/Makefile
>> +++ b/fs/btrfs/Makefile
>> @@ -9,7 +9,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
>> export.o tree-log.o free-space-cache.o zlib.o lzo.o \
>> compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
>> reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
>> - uuid-tree.o props.o
>> + uuid-tree.o props.o hash.o
>>
>> btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
>> btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 77acc08..db19ed7 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -1072,11 +1072,11 @@ static u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset)
>> __le64 lenum;
>>
>> lenum = cpu_to_le64(root_objectid);
>> - high_crc = crc32c(high_crc, &lenum, sizeof(lenum));
>> + high_crc = btrfs_crc32c(high_crc, &lenum, sizeof(lenum));
>> lenum = cpu_to_le64(owner);
>> - low_crc = crc32c(low_crc, &lenum, sizeof(lenum));
>> + low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
>> lenum = cpu_to_le64(offset);
>> - low_crc = crc32c(low_crc, &lenum, sizeof(lenum));
>> + low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
>>
>> return ((u64)high_crc << 31) ^ (u64)low_crc;
>> }
>> diff --git a/fs/btrfs/hash.c b/fs/btrfs/hash.c
>> new file mode 100644
>> index 0000000..ab3a938
>> --- /dev/null
>> +++ b/fs/btrfs/hash.c
>> @@ -0,0 +1,49 @@
>> +/*
>> + * Copyright (C) 2014 Filipe David Borba Manana <fdmanana@xxxxxxxxx>
>> + *
>> + * 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 "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;
>> +}
>> diff --git a/fs/btrfs/hash.h b/fs/btrfs/hash.h
>> index 1d98281..118a231 100644
>> --- a/fs/btrfs/hash.h
>> +++ b/fs/btrfs/hash.h
>> @@ -19,10 +19,15 @@
>> #ifndef __HASH__
>> #define __HASH__
>>
>> -#include <linux/crc32c.h>
>> +int __init btrfs_hash_init(void);
>> +
>> +void btrfs_hash_exit(void);
>> +
>> +u32 btrfs_crc32c(u32 crc, const void *address, unsigned int length);
>> +
>> static inline u64 btrfs_name_hash(const char *name, int len)
>> {
>> - return crc32c((u32)~1, name, len);
>> + return btrfs_crc32c((u32)~1, name, len);
>> }
>>
>> /*
>> @@ -31,7 +36,7 @@ static inline u64 btrfs_name_hash(const char *name, int len)
>> static inline u64 btrfs_extref_hash(u64 parent_objectid, const char *name,
>> int len)
>> {
>> - return (u64) crc32c(parent_objectid, name, len);
>> + return (u64) btrfs_crc32c(parent_objectid, name, len);
>> }
>>
>> #endif
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index 461e41c..f44cc6a 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -48,6 +48,7 @@
>> #include "transaction.h"
>> #include "btrfs_inode.h"
>> #include "print-tree.h"
>> +#include "hash.h"
>> #include "props.h"
>> #include "xattr.h"
>> #include "volumes.h"
>> @@ -1866,11 +1867,15 @@ static int __init init_btrfs_fs(void)
>> {
>> int err;
>>
>> + err = btrfs_hash_init();
>> + if (err)
>> + return err;
>> +
>> btrfs_props_init();
>>
>> err = btrfs_init_sysfs();
>> if (err)
>> - return err;
>> + goto free_hash;
>>
>> btrfs_init_compress();
>>
>> @@ -1945,6 +1950,8 @@ free_cachep:
>> free_compress:
>> btrfs_exit_compress();
>> btrfs_exit_sysfs();
>> +free_hash:
>> + btrfs_hash_exit();
>> return err;
>> }
>>
>> @@ -1963,6 +1970,7 @@ static void __exit exit_btrfs_fs(void)
>> btrfs_exit_sysfs();
>> btrfs_cleanup_fs_uuids();
>> btrfs_exit_compress();
>> + btrfs_hash_exit();
>> }
>>
>> module_init(init_btrfs_fs)
>> --
>> 1.7.9.5
>>
>> --
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--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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