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Message-ID: <372ba741.6a64.180749d7078.Coremail.duoming@zju.edu.cn> Date: Fri, 29 Apr 2022 17:18:36 +0800 (GMT+08:00) From: duoming@....edu.cn To: "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org> Cc: linux-kernel@...r.kernel.org, kuba@...nel.org, gregkh@...uxfoundation.org, davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com, alexander.deucher@....com, akpm@...ux-foundation.org, broonie@...nel.org, netdev@...r.kernel.org, linma@....edu.cn Subject: Re: Re: [PATCH net v5 1/2] nfc: replace improper check device_is_registered() in netlink related functions Hello, On Fri, 29 Apr 2022 09:19:36 +0200 Krzysztof wrote: > > The device_is_registered() in nfc core is used to check whether > > nfc device is registered in netlink related functions such as > > nfc_fw_download(), nfc_dev_up() and so on. Although device_is_registered() > > is protected by device_lock, there is still a race condition between > > device_del() and device_is_registered(). The root cause is that > > kobject_del() in device_del() is not protected by device_lock. > > > > (cleanup task) | (netlink task) > > | > > nfc_unregister_device | nfc_fw_download > > device_del | device_lock > > ... | if (!device_is_registered)//(1) > > kobject_del//(2) | ... > > ... | device_unlock > > > > The device_is_registered() returns the value of state_in_sysfs and > > the state_in_sysfs is set to zero in kobject_del(). If we pass check in > > position (1), then set zero in position (2). As a result, the check > > in position (1) is useless. > > > > This patch uses bool variable instead of device_is_registered() to judge > > whether the nfc device is registered, which is well synchronized. > > > > Fixes: 3e256b8f8dfa ("NFC: add nfc subsystem core") > > Signed-off-by: Duoming Zhou <duoming@....edu.cn> > > --- > > Changes in v5: > > - Replace device_is_registered() to bool variable. > > > > include/net/nfc/nfc.h | 1 + > > net/nfc/core.c | 26 ++++++++++++++------------ > > 2 files changed, 15 insertions(+), 12 deletions(-) > > > > diff --git a/include/net/nfc/nfc.h b/include/net/nfc/nfc.h > > index 5dee575fbe8..7bb4ccb1830 100644 > > --- a/include/net/nfc/nfc.h > > +++ b/include/net/nfc/nfc.h > > @@ -167,6 +167,7 @@ struct nfc_dev { > > int n_targets; > > int targets_generation; > > struct device dev; > > + bool dev_register; > > bool dev_up; > > bool fw_download_in_progress; > > u8 rf_mode; > > diff --git a/net/nfc/core.c b/net/nfc/core.c > > index dc7a2404efd..52147da2286 100644 > > --- a/net/nfc/core.c > > +++ b/net/nfc/core.c > > @@ -38,7 +38,7 @@ int nfc_fw_download(struct nfc_dev *dev, const char *firmware_name) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -94,7 +94,7 @@ int nfc_dev_up(struct nfc_dev *dev) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -142,7 +142,7 @@ int nfc_dev_down(struct nfc_dev *dev) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -207,7 +207,7 @@ int nfc_start_poll(struct nfc_dev *dev, u32 im_protocols, u32 tm_protocols) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -246,7 +246,7 @@ int nfc_stop_poll(struct nfc_dev *dev) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -291,7 +291,7 @@ int nfc_dep_link_up(struct nfc_dev *dev, int target_index, u8 comm_mode) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -335,7 +335,7 @@ int nfc_dep_link_down(struct nfc_dev *dev) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -401,7 +401,7 @@ int nfc_activate_target(struct nfc_dev *dev, u32 target_idx, u32 protocol) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -448,7 +448,7 @@ int nfc_deactivate_target(struct nfc_dev *dev, u32 target_idx, u8 mode) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -495,7 +495,7 @@ int nfc_data_exchange(struct nfc_dev *dev, u32 target_idx, struct sk_buff *skb, > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > kfree_skb(skb); > > goto error; > > @@ -552,7 +552,7 @@ int nfc_enable_se(struct nfc_dev *dev, u32 se_idx) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -601,7 +601,7 @@ int nfc_disable_se(struct nfc_dev *dev, u32 se_idx) > > > > device_lock(&dev->dev); > > > > - if (!device_is_registered(&dev->dev)) { > > + if (!dev->dev_register) { > > rc = -ENODEV; > > goto error; > > } > > @@ -1134,6 +1134,7 @@ int nfc_register_device(struct nfc_dev *dev) > > dev->rfkill = NULL; > > } > > } > > + dev->dev_register = true; > > device_unlock(&dev->dev); > > > > rc = nfc_genl_device_added(dev); > > @@ -1166,6 +1167,7 @@ void nfc_unregister_device(struct nfc_dev *dev) > > rfkill_unregister(dev->rfkill); > > rfkill_destroy(dev->rfkill); > > } > > + dev->dev_register = false; > > We already have flag for it - dev->shutting_down. Currently it is used > only in if device implements check_presence but I think it can be easily > moved to common path. > > Having multiple fields for similar, but slightly different cases, is > getting us closer and closer to spaghetti code. Thanks a lot for your suggestion, I will move dev->shutting_down to common path. Best regards, Duoming Zhou
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