Messages in this thread | | | Date | Thu, 29 Nov 2001 08:06:37 -0800 (PST) | From | Balbir Singh <> | Subject | Re: Patch: Fix serial module use count (2.4.16 _and_ 2.5) |
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>Err, > close(-ENOMEM);
>What's that going to close? Hint: you _can't_ close a descriptor that >failed to open, since you don't have a descriptor to close. You can >only try to close an error code, but that's not going to make it anywhere >near the kernel driver level.
Let me make it clearer to you,
lets say I call rs_open() on /dev/ttyS0 and if it fails then I should not call rs_close() after a failed rs_open().
I hope this is clear now.
> The same thing applies to the code below. I think that the open routine > should instead set tty->driver_data to NULL upon failure.
>Here's an example why that'd be real bad:
>1. process A opens /dev/ttyS0 as a normal device. >This initialises > tty->driver_data. >2. process B tries to open /dev/cua0 >3. process B fails with -EBUSY since the normal >device is open and active > (see block_til_ready) >4. since rs_open failed, we set tty->driver_data to >be NULL (note that this > is the same tty device pointer as (1) above. >5. process A writes to /dev/ttyS0 >6. rs_write does the following:
> struct async_struct *info = (struct async_struct *)tty->driver_data;
>7. Oops.
Lets see what happens with your approach
1. I call rs_open(), it fails, ref_count set to 1
2. I am sane enough not to call rs_close() on the device which failed to open with rs_open the first time, count is set to 1, driver never unloads.
I do not have access to block_til_ready currently. But, I will see that function and revert with more comments.
Comments, Balbir Singh.
-- Russell King (rmk@arm.linux.org.uk) The developer of ARM Linux
http://www.arm.linux.org.uk/personal/aboutme.html
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