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30 Mar 2025 14:32:22 +0200 Message-ID: <45cee3c7-e1b2-4058-bc81-c6eb5935fad0@o2.pl> Date: Sun, 30 Mar 2025 14:32:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [ BUG: Invalid wait context ] rtc_lock at: mc146818_avoid_UIP From: =?UTF-8?Q?Mateusz_Jo=C5=84czyk?= To: Borislav Petkov , linux-rtc@vger.kernel.org, Alexandre Belloni Cc: lkml , Anna-Maria Behnsen , Frederic Weisbecker , Thomas Gleixner References: <20250330113202.GAZ-krsjAnurOlTcp-@fat_crate.local> <947b1ceb-77a3-439b-bb7b-6eba38e12cb3@o2.pl> Content-Language: en-GB, pl Autocrypt: addr=mat.jonczyk@o2.pl; keydata= xsFNBFqMDyQBEAC2VYhOvwXdcGfmMs9amNUFjGFgLixeS2C1uYwaC3tYqjgDQNo/qDoPh52f ExoTMJRqx48qvvY/i6iwia7wOTBxbYCBDqGYxDudjtL41ko8AmbGOSkxJww5X/2ZAtFjUJxO QjNESFlRscMfDv5vcCvtH7PaJJob4TBZvKxdL4VCDCgEsmOadTy5hvwv0rjNjohau1y4XfxU DdvOcl6LpWMEezsHGc/PbSHNAKtVht4BZYg66kSEAhs2rOTN6pnWJVd7ErauehrET2xo2JbO 4lAv0nbXmCpPj37ZvURswCeP8PcHoA1QQKWsCnHU2WeVw+XcvR/hmFMI2QnE6V/ObHAb9bzg jxSYVZRAWVsdNakfT7xhkaeHjEQMVRQYBL6bqrJMFFXyh9YDj+MALjyb5hDG3mUcB4Wg7yln DRrda+1EVObfszfBWm2pC9Vz1QUQ4CD88FcmrlC7n2witke3gr38xmiYBzDqi1hRmrSj2WnS RP/s9t+C8M8SweQ2WuoVBLWUvcULYMzwy6mte0aSA8XV6+02a3VuBjP/6Y8yZUd0aZfAHyPi Rf60WVjYNRSeg27lZ9DJmHjSfZNn1FrtZi3W9Ff6bry/SY9D136qXBQxPYxXQfaGDhVeLUVF Q+NIZ6NEjqrLQ07LEvUW2Qzk2q851/IaXZPtP6swx0gqrpjNrwARAQABzSRNYXRldXN6IEpv xYRjenlrIDxtYXQuam9uY3p5a0BvMi5wbD7CwX4EEwECACgFAlqMDyQCGwMFCRLMAwAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEPvWWrhhCv7Gb0MQAJVIpJ1KAOH6WaT8e65xZulI 1jkwGwNp+3bWWc5eLjKUnXtOYpa9oIsUUAqvh/L8MofGtM1V11kSX9dEloyqlqDyNSQk0h52 hZxMsCQyzjGOcBAi0zmWGYB4xu6SXj4LpVpIPW0sogduEOfbC0i7uAIyotHgepQ8RPGmZoXU 9bzFCyqZ8kAqwOoCCx+ccnXtbnlAXQmDb88cIprAU+Elk4k4t7Bpjn2ek4fv35PsvsBdRTq3 ADg8sGuq4KQXhbY53n1tyiab3M88uv6Cv//Ncgx+AqMdXq2AJ7amFsYdvkTC98sx20qk6Cul oHggmCre4MBcDD4S0qDXo5Z9NxVR/e9yUHxGLc5BlNj+FJPO7zwvkmIaMMnMlbydWVke0FSR AzJaEV/NNZKYctw2wYThdXPiz/y7aKd6/sM1jgPlleQhs3tZAIdjPfFjGdeeggv668M7GmKl +SEzpeFQ4b0x64XfLfLXX8GP/ArTuxEfJX4L05/Y9w9AJwXCVEwW4q17v8gNsPyVUVEdIroK cve6cgNNSWoxTaYcATePmkKnrAPqfg+6qFM4TuOWmyzCLQ1YoUZMxH+ddivDQtlKCp6JgGCz c9YCESxVii0vo8TsHdIAjQ/px9KsuYBmOlKnHXKbj6BsE/pkMMKQg/L415dvKzhLm2qVih7I U16IAtK5b7RpzsFNBFqMDyQBEACclVvbzpor4XfU6WLUofqnO3QSTwDuNyoNQaE4GJKEXA+p Bw5/D2ruHhj1Bgs6Qx7G4XL3odzO1xT3Iz6w26ZrxH69hYjeTdT8VW4EoYFvliUvgye2cC01 ltYrMYV1IBXwJqSEAImU0Xb+AItAnHA1NNUUb9wKHvOLrW4Y7Ntoy1tp7Vww2ecAWEIYjcO6 AMoUX8Q6gfVPxVEQv1EpspSwww+x/VlDGEiiYO4Ewm4MMSP4bmxsTmPb/f/K3rv830ZCQ5Ds U0rzUMG2CkyF45qXVWZ974NqZIeVCTE+liCTU7ARX1bN8VlU/yRs/nP2ISO0OAAMBKea7slr mu93to9gXNt3LEt+5aVIQdwEwPcqR09vGvTWdRaEQPqgkOJFyiZ0vYAUTwtITyjYxZWJbKJh JFaHpMds9kZLF9bH45SGb64uZrrE2eXTyI3DSeUS1YvMlJwKGumRTPXIzmVQ5PHiGXr2/9S4 16W9lBDJeHhmcVOsn+04x5KIxHtqAP3mkMjDBYa0A3ksqD84qUBNuEKkZKgibBbs4qT35oXf kgWJtW+JziZf6LYx4WvRa80VDIIYCcQM6TrpsXIJI+su5qpzON1XJQG2iswY8PJ40pkRI9Sm kfTFrHOgiTpwZnI9saWqJh2ABavtnKZ1CtAY2VA8gmEqQeqs2hjdiNHAmRxR2wARAQABwsFl BBgBAgAPBQJajA8kAhsMBQkSzAMAAAoJEPvWWrhhCv7GhpYP/1tH/Kc35OgWu2lsgJxR9Z49 4q+yYAuu11p0aQidL5utMFiemYHvxh/sJ4vMq65uPQXoQ3vo8lu9YR/p8kEt8jbljJusw6xQ iKA1Cc68xtseiKcUrjmN/rk3csbT+Qj2rZwkgod8v9GlKo6BJXMcKGbHb1GJtLF5HyI1q4j/ zfeu7G1gVjGTx8e2OLyuBJp0HlFXWs2vWSMesmZQIBVNyyL9mmDLEwO4ULK2quF6RYtbvg+2 PMyomNAaQB4s1UbXAO87s75hM79iszIzak2am4dEjTx+uYCWpvcw3rRDz7aMs401CphrlMKr WndS5qYcdiS9fvAfu/Jp5KIawpM0tVrojnKWCKHG4UnJIn+RF26+E7bjzE/Q5/NpkMblKD/Y 6LHzJWsnLnL1o7MUARU++ztOl2Upofyuj7BSath0N632+XCTXk9m5yeDCl/UzPbP9brIChuw gF7DbkdscM7fkYzkUVRJM45rKOupy5Z03EtAzuT5Z/If3qJPU0txAJsquDohppFsGHrzn/X2 0nI2LedLnIMUWwLRT4EvdYzsbP6im/7FXps15jaBOreobCaWTWtKtwD2LNI0l9LU9/RF+4Ac gwYu1CerMmdFbSo8ZdnaXlbEHinySUPqKmLHmPgDfxKNhfRDm1jJcGATkHCP80Fww8Ihl8aS TANkZ3QqXNX2 In-Reply-To: <947b1ceb-77a3-439b-bb7b-6eba38e12cb3@o2.pl> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-WP-MailID: e47304061ecc448764be7d6522469e98 X-WP-AV: skaner antywirusowy Poczty o2 X-WP-SPAM: NO 0000000 [obM0] W dniu 30.03.2025 o 14:23, Mateusz Jończyk pisze: > W dniu 30.03.2025 o 13:32, Borislav Petkov pisze: >> So, >> >> while playing with suspend to RAM, I got this lockdep splat below. >> >> Poking around I found: >> >> ec5895c0f2d8 ("rtc: mc146818-lib: extract mc146818_avoid_UIP") >> >> which is doing this funky taking and dropping the rtc_lock and I >> guess that's >> inherited from ye olde times. >> >> I "fixed" it so lockdeup doesn't warn by converting rtc_lock to a raw >> spinlock >> but this is definitely not the right fix so let me bounce it off to >> the folks >> on Cc who might have a better idea perhaps... >> >> Thx. > > Hello, > > This problem has been reported before, see > > https://lore.kernel.org/all/463fbc29-b41f-4d2d-a869-108114000cdb@o2.pl/ > > I started work on converting rtc_lock to a raw spinlock, but got stuck > mostly to a lack > of time etc. Only did some MIPS patches (unpublished). > > The problem is that timekeeping_suspend() takes a raw spinlock called > "tk_core.lock". > With this lock taken, this function indirectly calls > mc146818_avoid_UIP(), which takes > a normal spinlock called "rtc_lock". It is necessary to take the > rtc_lock while accessing > the RTC: the RTC access cycle consists of writing to an index register > and then accessing > the data register. If something else touches the index register in the > middle, we get garbage. > > During a RTC tick, the RTC date/time registers are in an unspecified > state - roughly during this > time the UIP (Update In Progress) bit in an RTC register A is set. > This is handled by > mc146818_avoid_UIP(). This function takes and releases the rtc_lock > multiple times, > in order not to hold it for too long a time (while sleeping). I meant "while waiting / while calling udelay()". mc146818_avoid_UIP() does not sleep. > But the rtc_lock does need to be taken anyway. > > So the solutions would be: > > 1. Change the rtc_lock to a raw spinlock. > > 2. Change the tick_freeze_lock to a normal spinlock (if possible). > > 3. Possibly rewrite mc146818_avoid_UIP to avoid taking the rtc_lock if > the tick_freeze_lock is held (likely ugly). > > 4. Maybe something else I haven't thought about. > > Thanks, > > Mateusz Greetings, Mateusz