Messages in this thread Patch in this message | | | Date | Fri, 12 Feb 2010 11:48:27 -0500 | From | Jeff Mahoney <> | Subject | [PATCH] delayacct: align to 8 byte boundary on 64-bit systems |
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prepare_reply sets up an skb for the response. If I understand it correctly, the payload contains:
+--------------------------------+ | genlmsghdr - 4 bytes | +--------------------------------+ | NLA header - 4 bytes | /* Aggregate header */ +-+------------------------------+ | | NLA header - 4 bytes | /* PID header */ | +------------------------------+ | | pid/tgid - 4 bytes | | +------------------------------+ | | NLA header - 4 bytes | /* stats header */ | + -----------------------------+ <- oops. aligned on 4 byte boundary | | struct taskstats - 328 bytes | +-+------------------------------+
The start of the taskstats struct must be 8 byte aligned on IA64 (and other systems with 8 byte alignment rules for 64-bit types) or runtime alignment warnings will be issued.
This patch pads the pid/tgid field out to sizeof(long), which forces the alignment of taskstats. The getdelays userspace code is ok with this since it assumes 32-bit pid/tgid and then honors that header's length field.
An array is used to avoid exposing kernel memory contents to userspace in the response.
Signed-off-by: Jeff Mahoney <jeffm@suse.com> --- kernel/taskstats.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/kernel/taskstats.c +++ b/kernel/taskstats.c @@ -362,6 +362,12 @@ static struct taskstats *mk_reply(struct struct nlattr *na, *ret; int aggr; + /* If we don't pad, we end up with alignment on a 4 byte boundary. + * This causes lots of runtime warnings on systems requiring 8 byte + * alignment */ + u32 pids[2] = { pid, 0 }; + int pid_size = ALIGN(sizeof(pid), sizeof(long)); + aggr = (type == TASKSTATS_TYPE_PID) ? TASKSTATS_TYPE_AGGR_PID : TASKSTATS_TYPE_AGGR_TGID; @@ -369,7 +375,7 @@ static struct taskstats *mk_reply(struct na = nla_nest_start(skb, aggr); if (!na) goto err; - if (nla_put(skb, type, sizeof(pid), &pid) < 0) + if (nla_put(skb, type, pid_size, pids) < 0) goto err; ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats)); if (!ret) -- Jeff Mahoney SUSE Labs
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