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[PATCH 4.6 069/100] TTY: n_gsm, fix false positive WARN_ON

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4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Slaby <jslaby@suse.cz>

commit d175feca89a1c162f60f4e3560ca7bc9437c65eb upstream.

Dmitry reported, that the current cleanup code in n_gsm can trigger a
warning:
WARNING: CPU: 2 PID: 24238 at drivers/tty/n_gsm.c:2048 gsm_cleanup_mux+0x166/0x6b0()
...
Call Trace:
...
 [<ffffffff81247ab9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:490
 [<ffffffff828d0456>] gsm_cleanup_mux+0x166/0x6b0 drivers/tty/n_gsm.c:2048
 [<ffffffff828d4d87>] gsmld_open+0x5b7/0x7a0 drivers/tty/n_gsm.c:2386
 [<ffffffff828b9078>] tty_ldisc_open.isra.2+0x78/0xd0 drivers/tty/tty_ldisc.c:447
 [<ffffffff828b973a>] tty_set_ldisc+0x1ca/0xa70 drivers/tty/tty_ldisc.c:567
 [<     inline     >] tiocsetd drivers/tty/tty_io.c:2650
 [<ffffffff828a14ea>] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2883
...

But this is a legal path when open fails to find a space in the
gsm_mux array and tries to clean up. So make it a standard test
instead of a warning.

Reported-by: "Dmitry Vyukov" <dvyukov@google.com>
Cc: Alan Cox <alan@linux.intel.com>
Link: http://lkml.kernel.org/r/CACT4Y+bHQbAB68VFi7Romcs-Z9ZW3kQRvcq+BvHH1oa5NcAdLA@mail.gmail.com
Fixes: 5a640967 ("tty/n_gsm.c: fix a memory leak in gsmld_open()")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/n_gsm.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2045,7 +2045,9 @@ static void gsm_cleanup_mux(struct gsm_m
 		}
 	}
 	spin_unlock(&gsm_mux_lock);
-	WARN_ON(i == MAX_MUX);
+	/* open failed before registering => nothing to do */
+	if (i == MAX_MUX)
+		return;
 
 	/* In theory disconnecting DLCI 0 is sufficient but for some
 	   modems this is apparently not the case. */

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[PATCH 4.6 000/100] 4.6.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 074/100] serial: 8250_mid: recognize interrupt source in handler Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 070/100] tty/serial: atmel: fix hardware handshake selection Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 077/100] clk: bcm2835: add locking to pll*_on/off methods Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 069/100] TTY: n_gsm, fix false positive WARN_ON Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 055/100] usb: misc: usbtest: fix pattern tests for scatterlists. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 073/100] serial: 8250_mid: use proper bar for DNV platform Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 079/100] watchdog: sp5100_tco: properly check for new register layouts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 071/100] Fix OpenSSH pty regression on close Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 056/100] USB: leave LPM alone if possible when binding/unbinding interface drivers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 022/100] fscrypto/f2fs: allow fs-specific key prefix for fs encryption Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 076/100] locking,qspinlock: Fix spin_is_locked() and spin_unlock_wait() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 007/100] kvm: arm64: Fix EC field in inject_abt64 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 068/100] tty: vt, return error when con_startup fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 067/100] x86/cpufeature, x86/mm/pkeys: Fix broken compile-time disabling of pkeys Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 042/100] mei: amthif: discard not read messages Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 008/100] perf/x86/intel/uncore: Remove WARN_ON_ONCE in uncore_pci_probe Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 066/100] xen/x86: actually allocate legacy interrupts on PV guests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 043/100] mei: bus: call mei_cl_read_start under device lock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 081/100] Fixing oops in callback path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 059/100] usb: host: xhci-rcar: Avoid long wait in xhci_reset() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 044/100] USB: serial: cp210x: fix hardware flow-control disable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 060/100] staging: comedi: das1800: fix possible NULL dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 039/100] Bluetooth: vhci: purge unhandled skbs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 038/100] Bluetooth: vhci: fix open_timeout vs. hdev race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 016/100] ring-buffer: Prevent overflow of size in ring_buffer_resize() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 033/100] mmc: sdhci-acpi: Remove MMC_CAP_BUS_WIDTH_TEST for Intel controllers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 037/100] mmc: sdhci-pci: Remove MMC_CAP_BUS_WIDTH_TEST for Intel controllers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 031/100] ACPI / PM: Export acpi_device_fix_up_power() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 027/100] irqchip/gic-v3: Configure all interrupts as non-secure Group-1 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 036/100] mmc: longer timeout for long read time quirk Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 020/100] clk: qcom: msm8916: Fix crypto clock flags Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 024/100] mfd: omap-usb-tll: Fix scheduling while atomic BUG Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 018/100] crypto: talitos - fix ahash algorithms registration Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 002/100] arm64: Ensure pmd_present() returns false after pmd_mknotpresent() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 025/100] Input: pwm-beeper - fix - scheduling while atomic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 026/100] irqchip/gic: Ensure ordering between read of INTACK and shared data Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 030/100] mmc: mmc: Fix partition switch timeout for some eMMCs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 003/100] arm64: Implement ptep_set_access_flags() for hardware AF/DBM Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 019/100] crypto: sun4i-ss - Replace spinlock_bh by spin_lock_irq{save|restore} Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 023/100] sched/loadavg: Fix loadavg artifacts on fully idle and on fully loaded systems Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 017/100] crypto: caam - fix caam_jr_alloc() ret code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 034/100] ACPI / osi: Fix an issue that acpi_osi=!* cannot disable ACPICA internal strings Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  Re: [PATCH 4.6 000/100] 4.6.1-stable review Guenter Roeck <linux@roeck-us.net> - 2016-06-01 07:40 +0200
    Re: [PATCH 4.6 000/100] 4.6.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-01 18:20 +0200
      Re: [PATCH 4.6 000/100] 4.6.1-stable review "Xuetao Guan" <gxt@mprc.pku.edu.cn> - 2016-06-02 06:40 +0200
  Re: [PATCH 4.6 000/100] 4.6.1-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-06-01 16:30 +0200

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