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    Subject[PATCH 3.10 1/9] ext4: atomically set inode->i_flags in ext4_set_inode_flags()
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Theodore Ts'o <tytso@mit.edu>

    commit 00a1a053ebe5febcfc2ec498bd894f035ad2aa06 upstream.

    Use cmpxchg() to atomically set i_flags instead of clearing out the
    S_IMMUTABLE, S_APPEND, etc. flags and then setting them from the
    EXT4_IMMUTABLE_FL, EXT4_APPEND_FL flags, since this opens up a race
    where an immutable file has the immutable flag cleared for a brief
    window of time.

    Reported-by: John Sullivan <jsrhbz@kanargh.force9.co.uk>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/inode.c | 15 +++++++++------
    include/linux/bitops.h | 15 +++++++++++++++
    2 files changed, 24 insertions(+), 6 deletions(-)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -38,6 +38,7 @@
    #include <linux/slab.h>
    #include <linux/ratelimit.h>
    #include <linux/aio.h>
    +#include <linux/bitops.h>

    #include "ext4_jbd2.h"
    #include "xattr.h"
    @@ -4044,18 +4045,20 @@ int ext4_get_inode_loc(struct inode *ino
    void ext4_set_inode_flags(struct inode *inode)
    {
    unsigned int flags = EXT4_I(inode)->i_flags;
    + unsigned int new_fl = 0;

    - inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
    if (flags & EXT4_SYNC_FL)
    - inode->i_flags |= S_SYNC;
    + new_fl |= S_SYNC;
    if (flags & EXT4_APPEND_FL)
    - inode->i_flags |= S_APPEND;
    + new_fl |= S_APPEND;
    if (flags & EXT4_IMMUTABLE_FL)
    - inode->i_flags |= S_IMMUTABLE;
    + new_fl |= S_IMMUTABLE;
    if (flags & EXT4_NOATIME_FL)
    - inode->i_flags |= S_NOATIME;
    + new_fl |= S_NOATIME;
    if (flags & EXT4_DIRSYNC_FL)
    - inode->i_flags |= S_DIRSYNC;
    + new_fl |= S_DIRSYNC;
    + set_mask_bits(&inode->i_flags,
    + S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC, new_fl);
    }

    /* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
    --- a/include/linux/bitops.h
    +++ b/include/linux/bitops.h
    @@ -185,6 +185,21 @@ static inline unsigned long __ffs64(u64

    #ifdef __KERNEL__

    +#ifndef set_mask_bits
    +#define set_mask_bits(ptr, _mask, _bits) \
    +({ \
    + const typeof(*ptr) mask = (_mask), bits = (_bits); \
    + typeof(*ptr) old, new; \
    + \
    + do { \
    + old = ACCESS_ONCE(*ptr); \
    + new = (old & ~mask) | bits; \
    + } while (cmpxchg(ptr, old, new) != old); \
    + \
    + new; \
    +})
    +#endif
    +
    #ifndef find_last_bit
    /**
    * find_last_bit - find the last set bit in a memory region



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