From f133bd4b5daf71bccdde0ad1a4f47fac76a6bfb1 Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:12:58 +0000 Subject: [PATCH 1/5] firmware: samsung: acpm: Fix cross-thread RX length corruption Sashiko identified a cross-thread RX length corruption bug when reviewing the thermal addition to ACPM [1]. When multiple threads concurrently send IPC requests, the ACPM polling mechanism can encounter responses belonging to other threads. To drain the queue, the driver saves these concurrent responses into an internal cache (`rx_data->cmd`) to be retrieved later by the owning thread. Previously, the driver incorrectly used `xfer->rxcnt` (the expected receive length of the *current* polling thread) when copying data for *other* threads into this cache. If the threads expected responses of different lengths, this resulted in buffer underflows (leading to reads of uninitialized memory) or potential buffer overflows. Fix this by replacing the boolean `response` flag in `struct acpm_rx_data` with `rxcnt`, caching the exact expected receive length for each specific transaction during transfer preparation. Use this cached length when saving concurrent responses. Consequently, ensure that `xfer->rxcnt` is explicitly zeroed in driver helpers (e.g., `acpm_dvfs_set_xfer`) for fire-and-forget messages to prevent uninitialized stack garbage from being interpreted as a massive expected receive length. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260420-acpm-tmu-v3-0-3dc8e93f0b26%40linaro.org [1] Reported-by: Titouan Ameline de Cadeville Closes: https://lore.kernel.org/r/20260426210255.73674-1-titouan.ameline@gmail.com/ Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-1-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski --- drivers/firmware/samsung/exynos-acpm-dvfs.c | 3 +++ drivers/firmware/samsung/exynos-acpm.c | 15 ++++++++------- 2 files changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/firmware/samsung/exynos-acpm-dvfs.c b/drivers/firmware/samsung/exynos-acpm-dvfs.c index 06bdf62dea1f..fdea7aa24ca0 100644 --- a/drivers/firmware/samsung/exynos-acpm-dvfs.c +++ b/drivers/firmware/samsung/exynos-acpm-dvfs.c @@ -31,6 +31,9 @@ static void acpm_dvfs_set_xfer(struct acpm_xfer *xfer, u32 *cmd, size_t cmdlen, if (response) { xfer->rxcnt = cmdlen; xfer->rxd = cmd; + } else { + xfer->rxcnt = 0; + xfer->rxd = NULL; } } diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index 16c46ed60837..e95edc350efa 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -104,12 +104,12 @@ struct acpm_queue { * * @cmd: pointer to where the data shall be saved. * @n_cmd: number of 32-bit commands. - * @response: true if the client expects the RX data. + * @rxcnt: expected length of the response in 32-bit words. */ struct acpm_rx_data { u32 *cmd; size_t n_cmd; - bool response; + size_t rxcnt; }; #define ACPM_SEQNUM_MAX 64 @@ -199,7 +199,7 @@ static void acpm_get_saved_rx(struct acpm_chan *achan, const struct acpm_rx_data *rx_data = &achan->rx_data[tx_seqnum - 1]; u32 rx_seqnum; - if (!rx_data->response) + if (!rx_data->rxcnt) return; rx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, rx_data->cmd[0]); @@ -256,7 +256,7 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) seqnum = rx_seqnum - 1; rx_data = &achan->rx_data[seqnum]; - if (rx_data->response) { + if (rx_data->rxcnt) { if (rx_seqnum == tx_seqnum) { __ioread32_copy(xfer->rxd, addr, xfer->rxcnt); rx_set = true; @@ -268,7 +268,8 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) * clear yet the bitmap. It will be cleared * after the response is copied to the request. */ - __ioread32_copy(rx_data->cmd, addr, xfer->rxcnt); + __ioread32_copy(rx_data->cmd, addr, + rx_data->rxcnt); } } else { clear_bit(seqnum, achan->bitmap_seqnum); @@ -380,8 +381,8 @@ static void acpm_prepare_xfer(struct acpm_chan *achan, /* Clear data for upcoming responses */ rx_data = &achan->rx_data[achan->seqnum - 1]; memset(rx_data->cmd, 0, sizeof(*rx_data->cmd) * rx_data->n_cmd); - if (xfer->rxd) - rx_data->response = true; + /* zero means no response expected */ + rx_data->rxcnt = xfer->rxcnt; /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ set_bit(achan->seqnum - 1, achan->bitmap_seqnum); From b66829b17f6385cc9ffbcbe2476d532d2e3121ad Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:12:59 +0000 Subject: [PATCH 2/5] firmware: samsung: acpm: Fix mailbox channel leak on probe error Sashiko identified the leak at [1]. The ACPM driver allocates hardware mailbox channels using `mbox_request_channel()` during `acpm_channels_init()`. However, the driver lacked a `.remove` callback and did not free these channels on subsequent error paths inside `acpm_probe()`. Additionally, if `acpm_achan_alloc_cmds()` failed during the channel initialization loop, the function returned immediately, bypassing the manual cleanup and permanently leaking any channels successfully requested in previous loop iterations. Fix this by modifying `acpm_free_mbox_chans()` to match the `devres` action signature and registering it via `devm_add_action_or_reset()`. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260420-acpm-tmu-v3-0-3dc8e93f0b26%40linaro.org [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-2-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski --- drivers/firmware/samsung/exynos-acpm.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index e95edc350efa..9766425a44ab 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -527,10 +527,11 @@ static int acpm_achan_alloc_cmds(struct acpm_chan *achan) /** * acpm_free_mbox_chans() - free mailbox channels. - * @acpm: pointer to driver data. + * @data: pointer to driver data. */ -static void acpm_free_mbox_chans(struct acpm_info *acpm) +static void acpm_free_mbox_chans(void *data) { + struct acpm_info *acpm = data; int i; for (i = 0; i < acpm->num_chans; i++) @@ -558,6 +559,10 @@ static int acpm_channels_init(struct acpm_info *acpm) if (!acpm->chans) return -ENOMEM; + ret = devm_add_action_or_reset(dev, acpm_free_mbox_chans, acpm); + if (ret) + return dev_err_probe(dev, ret, "Failed to add mbox free action.\n"); + chans_shmem = acpm->sram_base + readl(&shmem->chans); for (i = 0; i < acpm->num_chans; i++) { @@ -579,10 +584,8 @@ static int acpm_channels_init(struct acpm_info *acpm) cl->dev = dev; achan->chan = mbox_request_channel(cl, 0); - if (IS_ERR(achan->chan)) { - acpm_free_mbox_chans(acpm); + if (IS_ERR(achan->chan)) return PTR_ERR(achan->chan); - } } return 0; From c889b146478885344a220dd468e5a08de088cbc5 Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:13:02 +0000 Subject: [PATCH 3/5] firmware: samsung: acpm: Fix false timeouts and Use-After-Free in polling Sashiko identified severe races in the polling state machine [1]. In the ACPM driver's polling mode, threads waited for responses by monitoring the globally shared 'bitmap_seqnum'. This caused false timeouts because if a thread processed its response and freed the sequence number, a concurrent TX thread could immediately reallocate it before the polling thread woke up. Additionally, the driver suffered from a cross-thread Use-After-Free (UAF) preemption race. Previously, acpm_get_rx() cleared the sequence number of whichever RX message it drained from the hardware queue. This meant Thread A could globally free Thread B's sequence slot while Thread B was asleep. A new Thread C could then steal the slot, overwrite the buffer, and leave Thread B to wake up to corrupted state or a timeout. Fix this by rewriting the polling state machine: 1. Decouple polling from the global allocator by introducing a per-slot 'completed' flag, synchronized via smp_store_release() and smp_load_acquire(). 2. Strip acpm_get_saved_rx() out of acpm_get_rx() to make it a pure queue-draining function. Introduce a 'native_match' boolean argument which evaluates to true only if the thread natively processed its own sequence number during the call. This explicitly informs the polling loop whether it must retrieve its payload from the cross-thread cache. 3. Centralize the cache fallback and sequence number free (clear_bit) inside the polling loop. Crucially, the free operation now strictly targets the thread's own TX sequence number (xfer->txd[0]), rather than the drained RX sequence number. This enforces strict ownership: a thread only ever frees its own allocated sequence slot, and only at the exact moment it completes its poll, eliminating the UAF window. Furthermore, explicitly guard the 'native_match' assignment with an if (rx_seqnum == tx_seqnum) check, even for zero-length (no payload) responses. While an unguarded assignment wouldn't crash (because the cache fallback acpm_get_saved_rx() safely returns early on zero-length transfers) doing so would "lie" to the state machine. If a thread drained the queue and found another thread's zero-length message, setting native_match = true would falsely convince the polling loop that it natively handled its own response. Maintaining a rigorous state machine requires that native_match is only set when a thread explicitly processes its own sequence number. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260429-acpm-fixes-sashiko-reports-v3-0-47cf74ab09ad%40linaro.org [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-5-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski --- drivers/firmware/samsung/exynos-acpm.c | 68 ++++++++++++++++++-------- 1 file changed, 48 insertions(+), 20 deletions(-) diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index 9766425a44ab..620880d8820a 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -105,11 +105,14 @@ struct acpm_queue { * @cmd: pointer to where the data shall be saved. * @n_cmd: number of 32-bit commands. * @rxcnt: expected length of the response in 32-bit words. + * @completed: flag indicating if the firmware response has been fully + * processed. */ struct acpm_rx_data { u32 *cmd; size_t n_cmd; size_t rxcnt; + bool completed; }; #define ACPM_SEQNUM_MAX 64 @@ -204,26 +207,28 @@ static void acpm_get_saved_rx(struct acpm_chan *achan, rx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, rx_data->cmd[0]); - if (rx_seqnum == tx_seqnum) { + if (rx_seqnum == tx_seqnum) memcpy(xfer->rxd, rx_data->cmd, xfer->rxcnt * sizeof(*xfer->rxd)); - clear_bit(rx_seqnum - 1, achan->bitmap_seqnum); - } } /** * acpm_get_rx() - get response from RX queue. * @achan: ACPM channel info. * @xfer: reference to the transfer to get response for. + * @native_match: pointer to a boolean set to true if the thread natively + * processed its own sequence number during this call. * * Return: 0 on success, -errno otherwise. */ -static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) +static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer, + bool *native_match) { u32 rx_front, rx_seqnum, tx_seqnum, seqnum; const void __iomem *base, *addr; struct acpm_rx_data *rx_data; u32 i, val, mlen; - bool rx_set = false; + + *native_match = false; guard(mutex)(&achan->rx_lock); @@ -232,10 +237,8 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) tx_seqnum = FIELD_GET(ACPM_PROTOCOL_SEQNUM, xfer->txd[0]); - if (i == rx_front) { - acpm_get_saved_rx(achan, xfer, tx_seqnum); + if (i == rx_front) return 0; - } base = achan->rx.base; mlen = achan->mlen; @@ -259,8 +262,13 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) if (rx_data->rxcnt) { if (rx_seqnum == tx_seqnum) { __ioread32_copy(xfer->rxd, addr, xfer->rxcnt); - rx_set = true; - clear_bit(seqnum, achan->bitmap_seqnum); + /* + * Signal completion to the polling thread. + * Pairs with smp_load_acquire() in polling + * loop. + */ + smp_store_release(&rx_data->completed, true); + *native_match = true; } else { /* * The RX data corresponds to another request. @@ -270,9 +278,21 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) */ __ioread32_copy(rx_data->cmd, addr, rx_data->rxcnt); + /* + * Signal completion to the polling thread. + * Pairs with smp_load_acquire() in polling + * loop. + */ + smp_store_release(&rx_data->completed, true); } } else { - clear_bit(seqnum, achan->bitmap_seqnum); + /* + * Signal completion to the polling thread. + * Pairs with smp_load_acquire() in polling loop. + */ + smp_store_release(&rx_data->completed, true); + if (rx_seqnum == tx_seqnum) + *native_match = true; } i = (i + 1) % achan->qlen; @@ -281,13 +301,6 @@ static int acpm_get_rx(struct acpm_chan *achan, const struct acpm_xfer *xfer) /* We saved all responses, mark RX empty. */ writel(rx_front, achan->rx.rear); - /* - * If the response was not in this iteration of the queue, check if the - * RX data was previously saved. - */ - if (!rx_set) - acpm_get_saved_rx(achan, xfer, tx_seqnum); - return 0; } @@ -302,6 +315,7 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan, const struct acpm_xfer *xfer) { struct device *dev = achan->acpm->dev; + bool native_match; ktime_t timeout; u32 seqnum; int ret; @@ -310,12 +324,25 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan, timeout = ktime_add_us(ktime_get(), ACPM_POLL_TIMEOUT_US); do { - ret = acpm_get_rx(achan, xfer); + ret = acpm_get_rx(achan, xfer, &native_match); if (ret) return ret; - if (!test_bit(seqnum - 1, achan->bitmap_seqnum)) + /* + * Safely check if our specific transaction has been processed. + * smp_load_acquire prevents the CPU from speculatively + * executing subsequent instructions before the transaction is + * synchronized. + */ + if (smp_load_acquire(&achan->rx_data[seqnum - 1].completed)) { + /* Retrieve payload if another thread cached it for us */ + if (!native_match) + acpm_get_saved_rx(achan, xfer, seqnum); + + /* Relinquish ownership of the sequence slot */ + clear_bit(seqnum - 1, achan->bitmap_seqnum); return 0; + } /* Determined experimentally. */ udelay(20); @@ -380,6 +407,7 @@ static void acpm_prepare_xfer(struct acpm_chan *achan, /* Clear data for upcoming responses */ rx_data = &achan->rx_data[achan->seqnum - 1]; + rx_data->completed = false; memset(rx_data->cmd, 0, sizeof(*rx_data->cmd) * rx_data->n_cmd); /* zero means no response expected */ rx_data->rxcnt = xfer->rxcnt; From bf296f83a3ddab1ab875edc4e8862cb10553064f Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:13:03 +0000 Subject: [PATCH 4/5] firmware: samsung: acpm: Fix missing LKMM barriers in sequence allocator Sashiko identified memory ordering races in [1]. The ACPM driver uses a globally shared 'bitmap_seqnum' to track available sequence numbers. Even though threads now strictly free their own sequence numbers, the allocation and freeing of these bits across concurrent threads are effectively lockless operations and require explicit LKMM memory barriers. Previously, the driver used plain bitwise operators (test_bit, set_bit, clear_bit), which lack ordering guarantees. This creates two race conditions on weakly ordered architectures like ARM64: 1. Polling Release Violation: The polling thread copies its payload and calls clear_bit(). Without a release barrier, the CPU can reorder the memory operations, making the cleared bit globally visible before the payload reads have fully completed. 2. TX Acquire Violation: The TX thread loops on test_bit(), calls set_bit(), and then wipes the payload buffer via memset(). Without an acquire barrier, the CPU can speculatively execute the memset() before the bit is safely and formally claimed. If these reorderings overlap, a new TX thread can claim the sequence number and overwrite the buffer while the original polling thread is still actively reading from it. Fix this by upgrading the bitwise operators. Wrap the TX allocation in test_and_set_bit_lock() to establish formal LKMM Acquire semantics, and pair it with clear_bit_unlock() in the polling path to enforce Release semantics. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260423-acpm-fixes-sashiko-reports-v1-0-2217b790925e%40linaro.org [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-6-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski --- drivers/firmware/samsung/exynos-acpm.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index 620880d8820a..3fa9fe283be4 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -7,7 +7,7 @@ #include #include -#include +#include #include #include #include @@ -340,7 +340,7 @@ static int acpm_dequeue_by_polling(struct acpm_chan *achan, acpm_get_saved_rx(achan, xfer, seqnum); /* Relinquish ownership of the sequence slot */ - clear_bit(seqnum - 1, achan->bitmap_seqnum); + clear_bit_unlock(seqnum - 1, achan->bitmap_seqnum); return 0; } @@ -397,11 +397,18 @@ static void acpm_prepare_xfer(struct acpm_chan *achan, struct acpm_rx_data *rx_data; u32 *txd = (u32 *)xfer->txd; - /* Prevent chan->seqnum from being re-used */ + /* + * Prevent chan->seqnum from being re-used. + * test_and_set_bit_lock() provides formal LKMM Acquire semantics. + * It pairs with the RX thread's clear_bit_unlock() to ensure the CPU + * does not speculatively execute the rx_data buffer wipe (memset) + * before the sequence number is safely claimed. + */ do { if (++achan->seqnum == ACPM_SEQNUM_MAX) achan->seqnum = 1; - } while (test_bit(achan->seqnum - 1, achan->bitmap_seqnum)); + /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ + } while (test_and_set_bit_lock(achan->seqnum - 1, achan->bitmap_seqnum)); txd[0] |= FIELD_PREP(ACPM_PROTOCOL_SEQNUM, achan->seqnum); @@ -411,9 +418,6 @@ static void acpm_prepare_xfer(struct acpm_chan *achan, memset(rx_data->cmd, 0, sizeof(*rx_data->cmd) * rx_data->n_cmd); /* zero means no response expected */ rx_data->rxcnt = xfer->rxcnt; - - /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ - set_bit(achan->seqnum - 1, achan->bitmap_seqnum); } /** From 7fe40c32a33905302341797b5d12c541729dd08d Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:13:04 +0000 Subject: [PATCH 5/5] firmware: samsung: acpm: Fix infinite loop on sequence number exhaustion Sashiko identified a possible infinite loop [1]. ACPM IPC sequence numbers are tracked via a 64-bit bitmap. Previously, acpm_prepare_xfer() used a do...while loop to search for a free sequence number. If all 63 available sequence numbers are leaked due to transient hardware timeouts or mailbox failures, the bitmap becomes full. The next call to acpm_prepare_xfer() would enter an infinite loop. Fix this by utilizing the kernel's optimized bitmap search functions (find_next_zero_bit / find_first_zero_bit). If the pool is completely exhausted, log the failure and return -EBUSY to allow the kernel to fail gracefully instead of hanging. Furthermore, drop the allocation loop entirely. Because acpm_prepare_xfer() is strictly called under the 'tx_lock' mutex, sequence number allocations are perfectly serialized. If find_next_zero_bit() locates a free bit, a single test_and_set_bit_lock() is mathematically guaranteed to succeed. To enforce this locking invariant, wrap the allocation in a WARN_ON_ONCE. If the atomic set fails, it indicates the driver's mutex serialization is fundamentally broken. The warning generates a stack trace for debugging, while returning -EIO immediately aborts the transfer to prevent silent payload corruption. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260420-acpm-tmu-v3-0-3dc8e93f0b26%40linaro.org [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-7-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski --- drivers/firmware/samsung/exynos-acpm.c | 45 ++++++++++++++++++-------- 1 file changed, 31 insertions(+), 14 deletions(-) diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index 3fa9fe283be4..19db3674a28f 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -390,34 +391,48 @@ static int acpm_wait_for_queue_slots(struct acpm_chan *achan, u32 next_tx_front) * TX queue. * @achan: ACPM channel info. * @xfer: reference to the transfer being prepared. + * + * Return: 0 on success, -errno otherwise. */ -static void acpm_prepare_xfer(struct acpm_chan *achan, - const struct acpm_xfer *xfer) +static int acpm_prepare_xfer(struct acpm_chan *achan, + const struct acpm_xfer *xfer) { struct acpm_rx_data *rx_data; u32 *txd = (u32 *)xfer->txd; + unsigned long size = ACPM_SEQNUM_MAX - 1; + unsigned long bit = achan->seqnum; + + bit = find_next_zero_bit(achan->bitmap_seqnum, size, bit); + if (bit >= size) { + bit = find_first_zero_bit(achan->bitmap_seqnum, size); + if (bit >= size) { + dev_err_ratelimited(achan->acpm->dev, + "ACPM sequence number pool exhausted\n"); + return -EBUSY; + } + } /* - * Prevent chan->seqnum from being re-used. - * test_and_set_bit_lock() provides formal LKMM Acquire semantics. - * It pairs with the RX thread's clear_bit_unlock() to ensure the CPU - * does not speculatively execute the rx_data buffer wipe (memset) - * before the sequence number is safely claimed. + * Execute the atomic set to formally claim the bit and establish + * LKMM Acquire semantics against the RX thread's clear_bit_unlock(). + * A loop is unnecessary because allocations are strictly serialized + * by tx_lock. */ - do { - if (++achan->seqnum == ACPM_SEQNUM_MAX) - achan->seqnum = 1; - /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ - } while (test_and_set_bit_lock(achan->seqnum - 1, achan->bitmap_seqnum)); + if (WARN_ON_ONCE(test_and_set_bit_lock(bit, achan->bitmap_seqnum))) + return -EIO; + /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ + achan->seqnum = bit + 1; txd[0] |= FIELD_PREP(ACPM_PROTOCOL_SEQNUM, achan->seqnum); /* Clear data for upcoming responses */ - rx_data = &achan->rx_data[achan->seqnum - 1]; + rx_data = &achan->rx_data[bit]; rx_data->completed = false; memset(rx_data->cmd, 0, sizeof(*rx_data->cmd) * rx_data->n_cmd); /* zero means no response expected */ rx_data->rxcnt = xfer->rxcnt; + + return 0; } /** @@ -477,7 +492,9 @@ int acpm_do_xfer(struct acpm_handle *handle, const struct acpm_xfer *xfer) if (ret) return ret; - acpm_prepare_xfer(achan, xfer); + ret = acpm_prepare_xfer(achan, xfer); + if (ret) + return ret; /* Write TX command. */ __iowrite32_copy(achan->tx.base + achan->mlen * tx_front,