| From | Greg Kroah-Hartman <> | Subject | [ 065/127] cfg80211: fix possible circular lock on reg_regdb_search() | Date | Fri, 28 Sep 2012 13:33:58 -0700 |
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3.0-stable review patch. If anyone has any objections, please let me know.
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From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
commit a85d0d7f3460b1a123b78e7f7e39bf72c37dfb78 upstream.
When call_crda() is called we kick off a witch hunt search for the same regulatory domain on our internal regulatory database and that work gets kicked off on a workqueue, this is done while the cfg80211_mutex is held. If that workqueue kicks off it will first lock reg_regdb_search_mutex and later cfg80211_mutex but to ensure two CPUs will not contend against cfg80211_mutex the right thing to do is to have the reg_regdb_search() wait until the cfg80211_mutex is let go.
The lockdep report is pasted below.
cfg80211: Calling CRDA to update world regulatory domain
====================================================== [ INFO: possible circular locking dependency detected ] 3.3.8 #3 Tainted: G O ------------------------------------------------------- kworker/0:1/235 is trying to acquire lock: (cfg80211_mutex){+.+...}, at: [<816468a4>] set_regdom+0x78c/0x808 [cfg80211]
but task is already holding lock: (reg_regdb_search_mutex){+.+...}, at: [<81646828>] set_regdom+0x710/0x808 [cfg80211]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (reg_regdb_search_mutex){+.+...}: [<800a8384>] lock_acquire+0x60/0x88 [<802950a8>] mutex_lock_nested+0x54/0x31c [<81645778>] is_world_regdom+0x9f8/0xc74 [cfg80211]
-> #1 (reg_mutex#2){+.+...}: [<800a8384>] lock_acquire+0x60/0x88 [<802950a8>] mutex_lock_nested+0x54/0x31c [<8164539c>] is_world_regdom+0x61c/0xc74 [cfg80211]
-> #0 (cfg80211_mutex){+.+...}: [<800a77b8>] __lock_acquire+0x10d4/0x17bc [<800a8384>] lock_acquire+0x60/0x88 [<802950a8>] mutex_lock_nested+0x54/0x31c [<816468a4>] set_regdom+0x78c/0x808 [cfg80211]
other info that might help us debug this:
Chain exists of: cfg80211_mutex --> reg_mutex#2 --> reg_regdb_search_mutex
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(reg_regdb_search_mutex); lock(reg_mutex#2); lock(reg_regdb_search_mutex); lock(cfg80211_mutex);
*** DEADLOCK ***
3 locks held by kworker/0:1/235: #0: (events){.+.+..}, at: [<80089a00>] process_one_work+0x230/0x460 #1: (reg_regdb_work){+.+...}, at: [<80089a00>] process_one_work+0x230/0x460 #2: (reg_regdb_search_mutex){+.+...}, at: [<81646828>] set_regdom+0x710/0x808 [cfg80211]
stack backtrace: Call Trace: [<80290fd4>] dump_stack+0x8/0x34 [<80291bc4>] print_circular_bug+0x2ac/0x2d8 [<800a77b8>] __lock_acquire+0x10d4/0x17bc [<800a8384>] lock_acquire+0x60/0x88 [<802950a8>] mutex_lock_nested+0x54/0x31c [<816468a4>] set_regdom+0x78c/0x808 [cfg80211]
Reported-by: Felix Fietkau <nbd@openwrt.org> Tested-by: Felix Fietkau <nbd@openwrt.org> Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com> Reviewed-by: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: John W. Linville <linville@tuxdriver.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- net/wireless/reg.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/net/wireless/reg.c +++ b/net/wireless/reg.c @@ -331,6 +331,9 @@ static void reg_regdb_search(struct work struct reg_regdb_search_request *request; const struct ieee80211_regdomain *curdom, *regdom; int i, r; + bool set_reg = false; + + mutex_lock(&cfg80211_mutex); mutex_lock(®_regdb_search_mutex); while (!list_empty(®_regdb_search_list)) { @@ -346,9 +349,7 @@ static void reg_regdb_search(struct work r = reg_copy_regd(®dom, curdom); if (r) break; - mutex_lock(&cfg80211_mutex); - set_regdom(regdom); - mutex_unlock(&cfg80211_mutex); + set_reg = true; break; } } @@ -356,6 +357,11 @@ static void reg_regdb_search(struct work kfree(request); } mutex_unlock(®_regdb_search_mutex); + + if (set_reg) + set_regdom(regdom); + + mutex_unlock(&cfg80211_mutex); } static DECLARE_WORK(reg_regdb_work, reg_regdb_search);
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