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Message-ID: <dcbd7098-be09-4309-a95f-c613977be389@linux.dev>
Date: Tue, 6 Feb 2024 14:10:05 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc: arkadiusz.kubalewski@...el.com
Subject: Re: [patch net] dpll: fix possible deadlock during netlink dump
operation
On 06/02/2024 12:51, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@...dia.com>
>
> Recently, I've been hitting following deadlock warning during dpll pin
> dump:
>
> [52804.637962] ======================================================
> [52804.638536] WARNING: possible circular locking dependency detected
> [52804.639111] 6.8.0-rc2jiri+ #1 Not tainted
> [52804.639529] ------------------------------------------------------
> [52804.640104] python3/2984 is trying to acquire lock:
> [52804.640581] ffff88810e642678 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}, at: netlink_dump+0xb3/0x780
> [52804.641417]
> but task is already holding lock:
> [52804.642010] ffffffff83bde4c8 (dpll_lock){+.+.}-{3:3}, at: dpll_lock_dumpit+0x13/0x20
> [52804.642747]
> which lock already depends on the new lock.
>
> [52804.643551]
> the existing dependency chain (in reverse order) is:
> [52804.644259]
> -> #1 (dpll_lock){+.+.}-{3:3}:
> [52804.644836] lock_acquire+0x174/0x3e0
> [52804.645271] __mutex_lock+0x119/0x1150
> [52804.645723] dpll_lock_dumpit+0x13/0x20
> [52804.646169] genl_start+0x266/0x320
> [52804.646578] __netlink_dump_start+0x321/0x450
> [52804.647056] genl_family_rcv_msg_dumpit+0x155/0x1e0
> [52804.647575] genl_rcv_msg+0x1ed/0x3b0
> [52804.648001] netlink_rcv_skb+0xdc/0x210
> [52804.648440] genl_rcv+0x24/0x40
> [52804.648831] netlink_unicast+0x2f1/0x490
> [52804.649290] netlink_sendmsg+0x36d/0x660
> [52804.649742] __sock_sendmsg+0x73/0xc0
> [52804.650165] __sys_sendto+0x184/0x210
> [52804.650597] __x64_sys_sendto+0x72/0x80
> [52804.651045] do_syscall_64+0x6f/0x140
> [52804.651474] entry_SYSCALL_64_after_hwframe+0x46/0x4e
> [52804.652001]
> -> #0 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}:
> [52804.652650] check_prev_add+0x1ae/0x1280
> [52804.653107] __lock_acquire+0x1ed3/0x29a0
> [52804.653559] lock_acquire+0x174/0x3e0
> [52804.653984] __mutex_lock+0x119/0x1150
> [52804.654423] netlink_dump+0xb3/0x780
> [52804.654845] __netlink_dump_start+0x389/0x450
> [52804.655321] genl_family_rcv_msg_dumpit+0x155/0x1e0
> [52804.655842] genl_rcv_msg+0x1ed/0x3b0
> [52804.656272] netlink_rcv_skb+0xdc/0x210
> [52804.656721] genl_rcv+0x24/0x40
> [52804.657119] netlink_unicast+0x2f1/0x490
> [52804.657570] netlink_sendmsg+0x36d/0x660
> [52804.658022] __sock_sendmsg+0x73/0xc0
> [52804.658450] __sys_sendto+0x184/0x210
> [52804.658877] __x64_sys_sendto+0x72/0x80
> [52804.659322] do_syscall_64+0x6f/0x140
> [52804.659752] entry_SYSCALL_64_after_hwframe+0x46/0x4e
> [52804.660281]
> other info that might help us debug this:
>
> [52804.661077] Possible unsafe locking scenario:
>
> [52804.661671] CPU0 CPU1
> [52804.662129] ---- ----
> [52804.662577] lock(dpll_lock);
> [52804.662924] lock(nlk_cb_mutex-GENERIC);
> [52804.663538] lock(dpll_lock);
> [52804.664073] lock(nlk_cb_mutex-GENERIC);
> [52804.664490]
>
> The issue as follows: __netlink_dump_start() calls control->start(cb)
> with nlk->cb_mutex held. In control->start(cb) the dpll_lock is taken.
> Then nlk->cb_mutex is released and taken again in netlink_dump(), while
> dpll_lock still being held. That leads to ABBA deadlock when another
> CPU races with the same operation.
>
> Fix this by moving dpll_lock taking into dumpit() callback which ensures
> correct lock taking order.
>
> Fixes: 9d71b54b65b1 ("dpll: netlink: Add DPLL framework base functions")
> Signed-off-by: Jiri Pirko <jiri@...dia.com>
Good catch, thanks!
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> ---
> drivers/dpll/dpll_netlink.c | 20 ++++++--------------
> drivers/dpll/dpll_nl.c | 4 ----
> 2 files changed, 6 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/dpll/dpll_netlink.c b/drivers/dpll/dpll_netlink.c
> index 314bb3775465..4ca9ad16cd95 100644
> --- a/drivers/dpll/dpll_netlink.c
> +++ b/drivers/dpll/dpll_netlink.c
> @@ -1199,6 +1199,7 @@ int dpll_nl_pin_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> unsigned long i;
> int ret = 0;
>
> + mutex_lock(&dpll_lock);
> xa_for_each_marked_start(&dpll_pin_xa, i, pin, DPLL_REGISTERED,
> ctx->idx) {
> if (!dpll_pin_available(pin))
> @@ -1218,6 +1219,8 @@ int dpll_nl_pin_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> }
> genlmsg_end(skb, hdr);
> }
> + mutex_unlock(&dpll_lock);
> +
> if (ret == -EMSGSIZE) {
> ctx->idx = i;
> return skb->len;
> @@ -1373,6 +1376,7 @@ int dpll_nl_device_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> unsigned long i;
> int ret = 0;
>
> + mutex_lock(&dpll_lock);
> xa_for_each_marked_start(&dpll_device_xa, i, dpll, DPLL_REGISTERED,
> ctx->idx) {
> hdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid,
> @@ -1389,6 +1393,8 @@ int dpll_nl_device_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
> }
> genlmsg_end(skb, hdr);
> }
> + mutex_unlock(&dpll_lock);
> +
> if (ret == -EMSGSIZE) {
> ctx->idx = i;
> return skb->len;
> @@ -1439,20 +1445,6 @@ dpll_unlock_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
> mutex_unlock(&dpll_lock);
> }
>
> -int dpll_lock_dumpit(struct netlink_callback *cb)
> -{
> - mutex_lock(&dpll_lock);
> -
> - return 0;
> -}
> -
> -int dpll_unlock_dumpit(struct netlink_callback *cb)
> -{
> - mutex_unlock(&dpll_lock);
> -
> - return 0;
> -}
> -
> int dpll_pin_pre_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
> struct genl_info *info)
> {
> diff --git a/drivers/dpll/dpll_nl.c b/drivers/dpll/dpll_nl.c
> index eaee5be7aa64..1e95f5397cfc 100644
> --- a/drivers/dpll/dpll_nl.c
> +++ b/drivers/dpll/dpll_nl.c
> @@ -95,9 +95,7 @@ static const struct genl_split_ops dpll_nl_ops[] = {
> },
> {
> .cmd = DPLL_CMD_DEVICE_GET,
> - .start = dpll_lock_dumpit,
> .dumpit = dpll_nl_device_get_dumpit,
> - .done = dpll_unlock_dumpit,
> .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DUMP,
> },
> {
> @@ -129,9 +127,7 @@ static const struct genl_split_ops dpll_nl_ops[] = {
> },
> {
> .cmd = DPLL_CMD_PIN_GET,
> - .start = dpll_lock_dumpit,
> .dumpit = dpll_nl_pin_get_dumpit,
> - .done = dpll_unlock_dumpit,
> .policy = dpll_pin_get_dump_nl_policy,
> .maxattr = DPLL_A_PIN_ID,
> .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DUMP,
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