Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 18 Apr 2005 11:29:51 +1000 | From | Kingsley Cheung <> | Subject | Relayfs Question: Use of relay_reset(). Potential race? |
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On Wed, Mar 23, 2005 at 08:02:54PM +1100, kingsley@aurema.com wrote: > Hi > > I'm using relayfs to relay data from a kernel module to user space on > a SuSE 2.6.5 kernel. I'm not absolutely sure what version of relayfs > has been back ported to it.
Hi Tom,
Could you please have a look at the following use of relay_reset() in a kernel module as follows (compiled against pre-redux relayfs):
static int exec_fileop_notify(int rchan_id, struct file *filp, enum relay_fileop op) { if (unlikely(rchan_id != exec_cid)) { printk(KERN_ERR "%s - bad file number\n", __FUNCTION__); return -EBADF; }
switch (op) { case RELAY_FILE_OPEN: atomic_inc(&exec_client_cnt); break; case RELAY_FILE_CLOSE: if (atomic_dec_and_test(&exec_client_cnt) == 0) relay_reset(exec_cid); <--- break; default: /* do nothing */ break; }
return 0; }
Is that legitimate? The reason I ask is because I've been seeing garbled oopses with keventd and I've narrowed it to two things:
1) Inadequate locking on my part in the kernel module, which I have addressed separately.
2) A race with relay_reset() and keventd, which is probably of interest to you if you're still maintaining the pre-redux patches.
The race is due to the use of INIT_WORK in _reset_relay():
INIT_WORK(&rchan->wake_readers, NULL, NULL); INIT_WORK(&rchan->wake_writers, NULL, NULL);
However, at the time relay_reset() is called, it is possible that these work structures are still being used by keventd when under heavy loads. The workaround I've used to fix this is to call flush_scheduled_work() before calling reset_relay() in the kernel module. Perhaps that needs to be called in relay_reset() or _relay_reset()?
As well I'm not sure about the uses of INIT_WORK in _relay_realloc_buffer() and relay_release() - perhaps they need attention too. I understand, however, that flush_schedule_work() blocks and thus it probably shouldn't be used in certain areas of the relayfs code.
My thanks, -- Kingsley - 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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