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65b770468e
By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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| accessibility | ||
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| amba | ||
| ata | ||
| atm | ||
| auxdisplay | ||
| base | ||
| block | ||
| bluetooth | ||
| cdrom | ||
| char | ||
| clocksource | ||
| connector | ||
| cpufreq | ||
| cpuidle | ||
| crypto | ||
| dca | ||
| dio | ||
| dma | ||
| edac | ||
| eisa | ||
| firewire | ||
| firmware | ||
| gpio | ||
| gpu | ||
| hid | ||
| hwmon | ||
| i2c | ||
| ide | ||
| idle | ||
| ieee1394 | ||
| ieee802154 | ||
| infiniband | ||
| input | ||
| isdn | ||
| leds | ||
| lguest | ||
| macintosh | ||
| mca | ||
| md | ||
| media | ||
| memstick | ||
| message | ||
| mfd | ||
| misc | ||
| mmc | ||
| mtd | ||
| net | ||
| nubus | ||
| of | ||
| oprofile | ||
| parisc | ||
| parport | ||
| pci | ||
| pcmcia | ||
| platform | ||
| pnp | ||
| power | ||
| pps | ||
| ps3 | ||
| rapidio | ||
| regulator | ||
| rtc | ||
| s390 | ||
| sbus | ||
| scsi | ||
| serial | ||
| sh | ||
| sn | ||
| spi | ||
| ssb | ||
| staging | ||
| tc | ||
| telephony | ||
| thermal | ||
| uio | ||
| usb | ||
| uwb | ||
| video | ||
| virtio | ||
| vlynq | ||
| w1 | ||
| watchdog | ||
| xen | ||
| zorro | ||
| Kconfig | ||
| Makefile | ||