On 2012-09-12 2:12 AM, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx>
>
> 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 scheuled 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@xxxxxxxxxxx>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxxxxxxxx>
With this patch I get a slightly different report:
[ 9.480000] cfg80211: Calling CRDA to update world regulatory domain
[ 9.490000]
[ 9.490000] ======================================================
[ 9.490000] [ INFO: possible circular locking dependency detected ]
[ 9.490000] 3.3.8 #4 Tainted: G O
[ 9.490000] -------------------------------------------------------
[ 9.490000] kworker/0:1/235 is trying to acquire lock:
[ 9.490000] (reg_mutex#2){+.+...}, at: [<8164617c>] set_regdom+0x64/0x80c [cfg80211]
[ 9.490000]
[ 9.490000] but task is already holding lock:
[ 9.490000] (reg_regdb_search_mutex){+.+...}, at: [<81646830>] set_regdom+0x718/0x80c [cfg80211]
[ 9.490000]
[ 9.490000] which lock already depends on the new lock.
[ 9.490000]
[ 9.490000]
[ 9.490000] the existing dependency chain (in reverse order) is:
[ 9.490000]
[ 9.490000] -> #1 (reg_regdb_search_mutex){+.+...}:
[ 9.490000] [<800a8384>] lock_acquire+0x60/0x88
[ 9.490000] [<802950a8>] mutex_lock_nested+0x54/0x31c
[ 9.490000] [<81645778>] is_world_regdom+0x9f8/0xc74 [cfg80211]
[ 9.490000]
[ 9.490000] -> #0 (reg_mutex#2){+.+...}:
[ 9.490000] [<800a77b8>] __lock_acquire+0x10d4/0x17bc
[ 9.490000] [<800a8384>] lock_acquire+0x60/0x88
[ 9.490000] [<802950a8>] mutex_lock_nested+0x54/0x31c
[ 9.490000] [<8164617c>] set_regdom+0x64/0x80c [cfg80211]
[ 9.490000] [<816468ac>] set_regdom+0x794/0x80c [cfg80211]
[ 9.490000]
[ 9.490000] other info that might help us debug this:
[ 9.490000]
[ 9.490000] Possible unsafe locking scenario:
[ 9.490000]
[ 9.490000] CPU0 CPU1
[ 9.490000] ---- ----
[ 9.490000] lock(reg_regdb_search_mutex);
[ 9.490000] lock(reg_mutex#2);
[ 9.490000] lock(reg_regdb_search_mutex);
[ 9.490000] lock(reg_mutex#2);
[ 9.490000]
[ 9.490000] *** DEADLOCK ***
[ 9.490000]
[ 9.490000] 4 locks held by kworker/0:1/235:
[ 9.490000] #0: (events){.+.+..}, at: [<80089a00>] process_one_work+0x230/0x460
[ 9.490000] #1: (reg_regdb_work){+.+...}, at: [<80089a00>] process_one_work+0x230/0x460
[ 9.490000] #2: (cfg80211_mutex){+.+...}, at: [<81646824>] set_regdom+0x70c/0x80c [cfg80211]
[ 9.490000] #3: (reg_regdb_search_mutex){+.+...}, at: [<81646830>] set_regdom+0x718/0x80c [cfg80211]
[ 9.490000]
[ 9.490000] stack backtrace:
[ 9.490000] Call Trace:
[ 9.490000] [<80290fd4>] dump_stack+0x8/0x34
[ 9.490000] [<80291bc4>] print_circular_bug+0x2ac/0x2d8
[ 9.490000] [<800a77b8>] __lock_acquire+0x10d4/0x17bc
[ 9.490000] [<800a8384>] lock_acquire+0x60/0x88
[ 9.490000] [<802950a8>] mutex_lock_nested+0x54/0x31c
[ 9.490000] [<8164617c>] set_regdom+0x64/0x80c [cfg80211]
[ 9.490000] [<816468ac>] set_regdom+0x794/0x80c [cfg80211]
[ 9.490000]
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