• Jeff Mahoney's avatar
    taskstats: pad taskstats netlink response for aligment issues on ia64 · 4be2c95d
    Jeff Mahoney authored
    The taskstats structure is internally aligned on 8 byte boundaries but the
    layout of the aggregrate reply, with two NLA headers and the pid (each 4
    bytes), actually force the entire structure to be unaligned.  This causes
    the kernel to issue unaligned access warnings on some architectures like
    ia64.  Unfortunately, some software out there doesn't properly unroll the
    NLA packet and assumes that the start of the taskstats structure will
    always be 20 bytes from the start of the netlink payload.  Aligning the
    start of the taskstats structure breaks this software, which we don't
    want.  So, for now the alignment only happens on architectures that
    require it and those users will have to update to fixed versions of those
    packages.  Space is reserved in the packet only when needed.  This ifdef
    should be removed in several years e.g.  2012 once we can be confident
    that fixed versions are installed on most systems.  We add the padding
    before the aggregate since the aggregate is already a defined type.
    Commit 85893120 ("delayacct: align to 8 byte boundary on 64-bit systems")
    previously addressed the alignment issues by padding out the pid field.
    This was supposed to be a compatible change but the circumstances
    described above mean that it wasn't.  This patch backs out that change,
    since it was a hack, and introduces a new NULL attribute type to provide
    the padding.  Padding the response with 4 bytes avoids allocating an
    aligned taskstats structure and copying it back.  Since the structure
    weighs in at 328 bytes, it's too big to do it on the stack.
    Signed-off-by: default avatarJeff Mahoney <jeffm@suse.com>
    Reported-by: default avatarBrian Rogers <brian@xyzw.org>
    Cc: Jeff Mahoney <jeffm@suse.com>
    Cc: Guillaume Chazarain <guichaz@gmail.com>
    Cc: Balbir Singh <balbir@in.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
getdelays.c 12.8 KB