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    SubjectRe: News UBSAN warnings in aacraid
    On Mon, Nov 27, 2017 at 8:17 PM, Meelis Roos <mroos@linux.ee> wrote:
    > Tried 4.15-rc1 on an old 32-bit HP Netserver with aacraid card. Compared
    > to 4.14, there are new UBSAN warnings with timer related backtraces, so
    > the timespec64 change seems suspicious:

    > [ 12.228155] UBSAN: Undefined behaviour in drivers/scsi/aacraid/commsup.c:2514:49
    > [ 12.228229] signed integer overflow:
    > [ 12.228283] 964297611 * 250 cannot be represented in type 'long int'

    Thanks for reporting it! For reference, this is my change that got applied to
    aac_command_thread:

    @@ -2496,7 +2496,7 @@ int aac_command_thread(void *data)
    }
    if (!time_before(next_check_jiffies,next_jiffies)
    && ((difference = next_jiffies - jiffies) <= 0)) {
    - struct timeval now;
    + struct timespec64 now;
    int ret;

    /* Don't even try to talk to adapter if its sick */
    @@ -2506,15 +2506,15 @@ int aac_command_thread(void *data)
    next_check_jiffies = jiffies
    + ((long)(unsigned)check_interval)
    * HZ;
    - do_gettimeofday(&now);
    + ktime_get_real_ts64(&now);

    /* Synchronize our watches */
    - if (((1000000 - (1000000 / HZ)) > now.tv_usec)
    - && (now.tv_usec > (1000000 / HZ)))
    - difference = (((1000000 - now.tv_usec) * HZ)
    - + 500000) / 1000000;
    + if (((NSEC_PER_SEC - (NSEC_PER_SEC / HZ)) > now.tv_nsec)
    + && (now.tv_nsec > (NSEC_PER_SEC / HZ)))
    + difference = (((NSEC_PER_SEC -
    now.tv_nsec) * HZ)
    + + NSEC_PER_SEC / 2) / NSEC_PER_SEC;
    else {
    - if (now.tv_usec > 500000)
    + if (now.tv_nsec > NSEC_PER_SEC / 2)
    ++now.tv_sec;

    if (dev->sa_firmware)
    The problem is that a microsecond number (0 to 999999) multiplied by
    HZ (100 to 1024) always fits in a 32-bit integer, but the nanosecond
    number doesn't.
    We could make that a 64-bit division, but that would be fairly expensive.

    I'm trying to understand the bigger picture now, rather than simply
    attempting to do a simple conversion, but I don't see what we are
    actually trying to compute in 'difference' here.

    I think this chunk would solve the problem and result in the
    same behavior as before:

    --- a/drivers/scsi/aacraid/commsup.c
    +++ b/drivers/scsi/aacraid/commsup.c
    @@ -2511,8 +2511,8 @@ int aac_command_thread(void *data)
    /* Synchronize our watches */
    if (((NSEC_PER_SEC - (NSEC_PER_SEC / HZ)) > now.tv_nsec)
    && (now.tv_nsec > (NSEC_PER_SEC / HZ)))
    - difference = (((NSEC_PER_SEC -
    now.tv_nsec) * HZ)
    - + NSEC_PER_SEC / 2) / NSEC_PER_SEC;
    + difference = HZ + HZ / 2 -
    + now.tv_nsec / (NSEC_PER_SEC / HZ);
    else {
    if (now.tv_nsec > NSEC_PER_SEC / 2)
    ++now.tv_sec;
    but I don't see why we add in half a second here. Any ideas?

    Arnd

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