Re: [PATCH] tpm: Remove ineffective wmb() from tpm_pm_resume()

[Richard Lyu <richard.lyu@suse.com>]

On 2026/09/10 01:51, Jarkko Sakkinen wrote:
>On Tue, Sep 08, 2026 at 05:58:02PM +0800, Richard Lyu wrote:
>> The comment above the wmb() in tpm_pm_resume() states that the barrier
>> guarantees TPM_CHIP_FLAG_SUSPENDED is written last, so that hwrng does
>> not activate before the chip has been fully resumed.  It cannot do so:
>> it is placed after the store that clears the flag, and therefore does
>> not order the preceding resume work before that store.  It also has
>> nothing to pair with, as tpm_try_get_ops() contains no matching read
>> barrier.
>>
>> Drop the barrier along with the comment rather than leave a no-op
>> behind.  Should such ordering turn out to be needed, it would require
>> paired barriers or locking.
>>
>> Fixes: 99d464506255 ("tpm: Prevent hwrng from activating during resume")
>> Link: https://lore.kernel.org/all/a62fc816-259a-4d28-a265-e425bc17ed50@gmail.com/
>> Signed-off-by: Richard Lyu <richard.lyu@suse.com>
>
>I agree that wmb() is necessary but what is the bug here?
>
>Agree with the change but I'm not convinced about fixes tag here.

You're right. There is no actual bug being fixed here, so a Fixes tag is not
needed. This patch only removes redundant code. I will send a v2 without the
tag.

Best Regards,
Richard Lyu