Messages in this thread Patch in this message | | | Date | Wed, 31 Aug 2005 13:01:09 -0700 | From | Nishanth Aravamudan <> | Subject | [PATCH][Bug 5132] fix sys_poll() large timeout handling |
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Sorry everybody, forgot the most important Cc: :)
-Nish
Hi Andrew,
In looking at Bug 5132 and sys_poll(), I think there is a flaw in the current code.
The @timeout parameter to sys_poll() is in milliseconds but we compare it to (MAX_SCHEDULE_TIMEOUT / HZ), which is jiffies/jiffies-per-sec or seconds. That seems blatantly broken. Also, I think we are better served by converting to jiffies first then comparing, as opposed to converting our maximum to milliseconds (or seconds, incorrectly) and comparing.
Comments, suggestions for improvement?
Description: The current sys_poll() implementation does not seem to handle large timeouts correctly. Any value in milliseconds (@timeout) which exceeds the maximum representable jiffy value (MAX_SCHEDULE_TIMEOUT) should result in a MAX_SCHEDULE_TIMEOUT schedule_timeout() call. To achieve this, convert @timeout to jiffies first, then compare to MAX_SCHEDULE_TIMEOUT.
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
---
fs/select.c | 14 +++++++++----- 1 files changed, 9 insertions(+), 5 deletions(-)
diff -urpN 2.6.13/fs/select.c 2.6.13-dev/fs/select.c --- 2.6.13/fs/select.c 2005-08-28 17:46:14.000000000 -0700 +++ 2.6.13-dev/fs/select.c 2005-08-31 12:43:52.000000000 -0700 @@ -470,12 +470,16 @@ asmlinkage long sys_poll(struct pollfd _ return -EINVAL; if (timeout) { - /* Careful about overflow in the intermediate values */ - if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ) - timeout = (unsigned long)(timeout*HZ+999)/1000+1; - else /* Negative or overflow */ - timeout = MAX_SCHEDULE_TIMEOUT; + /* + * Convert the value from msecs to jiffies - if overflow + * occurs we get a negative value, which gets handled by + * the next block + */ + timeout = msecs_to_jiffies(timeout) + 1; } + if (timeout < 0) /* Negative requests result in infinite timeouts */ + timeout = MAX_SCHEDULE_TIMEOUT; + /* 0 case falls through */ poll_initwait(&table); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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