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| author | Paul Gortmaker <paul.gortmaker@windriver.com> | 2014-01-15 01:03:37 +0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-02-13 22:41:47 +0400 |
| commit | f76a1cbed18c86e2d192455f0daebb48458965f3 (patch) | |
| tree | 6372a788551489c9fc68dfb82627c1970bdde4b1 /drivers/tty | |
| parent | 9be16b38cf43181efc12ee6f467aaf222ad31b03 (diff) | |
| download | linux-f76a1cbed18c86e2d192455f0daebb48458965f3.tar.xz | |
hvc: ensure hvc_init is only ever called once in hvc_console.c
Commit 3e6c6f630a5282df8f3393a59f10eb9c56536d23 ("Delay creation of
khcvd thread") moved the call of hvc_init from being a device_initcall
into hvc_alloc, and used a non-null hvc_driver as indication of whether
hvc_init had already been called.
The problem with this is that hvc_driver is only assigned a value
at the bottom of hvc_init, and so there is a window where multiple
hvc_alloc calls can be in progress at the same time and hence try
and call hvc_init multiple times. Previously the use of device_init
guaranteed that hvc_init was only called once.
This manifests itself as sporadic instances of two hvc_init calls
racing each other, and with the loser of the race getting -EBUSY
from tty_register_driver() and hence that virtual console fails:
Couldn't register hvc console driver
virtio-ports vport0p1: error -16 allocating hvc for port
Here we add an atomic_t to guarantee we'll never run hvc_init twice.
Cc: stable@vger.kernel.org # v2.6.24+
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 3e6c6f630a52 ("Delay creation of khcvd thread")
Reported-by: Jim Somerville <Jim.Somerville@windriver.com>
Tested-by: Jim Somerville <Jim.Somerville@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/hvc/hvc_console.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 50b46881b6ca..94f9e3a38412 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -31,6 +31,7 @@ #include <linux/list.h> #include <linux/module.h> #include <linux/major.h> +#include <linux/atomic.h> #include <linux/sysrq.h> #include <linux/tty.h> #include <linux/tty_flip.h> @@ -70,6 +71,9 @@ static struct task_struct *hvc_task; /* Picks up late kicks after list walk but before schedule() */ static int hvc_kicked; +/* hvc_init is triggered from hvc_alloc, i.e. only when actually used */ +static atomic_t hvc_needs_init __read_mostly = ATOMIC_INIT(-1); + static int hvc_init(void); #ifdef CONFIG_MAGIC_SYSRQ @@ -851,7 +855,7 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data, int i; /* We wait until a driver actually comes along */ - if (!hvc_driver) { + if (atomic_inc_not_zero(&hvc_needs_init)) { int err = hvc_init(); if (err) return ERR_PTR(err); |