From ad0b65efd12d020b046cde8d6f474e37bb98dd73 Mon Sep 17 00:00:00 2001 From: Brandon Philips Date: Thu, 6 Nov 2008 11:19:11 -0800 Subject: [PATCH] USB: cdc-acm.c: fix recursive lock in acm_start_wb error path Fixes an obvious bug in cdc-acm by avoiding a recursive lock on acm_start_wb()'s error path. Should apply towards 2.6.27 stable and 2.6.28. ============================================= [ INFO: possible recursive locking detected ] 2.6.27-2-pae #109 --------------------------------------------- python/31449 is trying to acquire lock: (&acm->write_lock){++..}, at: [] acm_start_wb+0x5c/0x7b [cdc_acm] but task is already holding lock: (&acm->write_lock){++..}, at: [] acm_tty_write+0xe1/0x167 [cdc_acm] other info that might help us debug this: 2 locks held by python/31449: #0: (&tty->atomic_write_lock){--..}, at: [] tty_write_lock+0x14/0x3b #1: (&acm->write_lock){++..}, at: [] acm_tty_write+0xe1/0x167 [cdc_acm] stack backtrace: Pid: 31449, comm: python Not tainted 2.6.27-2-pae #109 [] ? printk+0xf/0x18 [] __lock_acquire+0xc7b/0x1316 [] lock_acquire+0x70/0x97 [] ? acm_start_wb+0x5c/0x7b [cdc_acm] [] _spin_lock_irqsave+0x37/0x47 [] ? acm_start_wb+0x5c/0x7b [cdc_acm] [] acm_start_wb+0x5c/0x7b [cdc_acm] [] acm_tty_write+0x143/0x167 [cdc_acm] [] write_chan+0x1cd/0x297 [] ? default_wake_function+0x0/0xd [] tty_write+0x149/0x1b9 [] ? write_chan+0x0/0x297 [] ? rw_verify_area+0x76/0x98 [] ? tty_write+0x0/0x1b9 [] vfs_write+0x8c/0x136 [] sys_write+0x3b/0x60 [] sysenter_do_call+0x12/0x3f ======================= Signed-off-by: Brandon Philips Cc: Oliver Neukum Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/usb/class/cdc-acm.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 20104443081..d50a99f70ae 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -158,16 +158,12 @@ static int acm_wb_is_avail(struct acm *acm) } /* - * Finish write. + * Finish write. Caller must hold acm->write_lock */ static void acm_write_done(struct acm *acm, struct acm_wb *wb) { - unsigned long flags; - - spin_lock_irqsave(&acm->write_lock, flags); wb->use = 0; acm->transmitting--; - spin_unlock_irqrestore(&acm->write_lock, flags); } /* @@ -482,6 +478,7 @@ static void acm_write_bulk(struct urb *urb) { struct acm_wb *wb = urb->context; struct acm *acm = wb->instance; + unsigned long flags; if (verbose || urb->status || (urb->actual_length != urb->transfer_buffer_length)) @@ -490,7 +487,9 @@ static void acm_write_bulk(struct urb *urb) urb->transfer_buffer_length, urb->status); + spin_lock_irqsave(&acm->write_lock, flags); acm_write_done(acm, wb); + spin_unlock_irqrestore(&acm->write_lock, flags); if (ACM_READY(acm)) schedule_work(&acm->work); else -- 2.20.1