From: Hongbo Li <lihongbo22@huawei.com>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bfoster@redhat.com>, <linux-bcachefs@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] bcachefs: eliminate the uninitialized compilation warning in __do_six_trylock
Date: Fri, 26 Apr 2024 14:09:53 +0800 [thread overview]
Message-ID: <4c7f35f0-29c2-4368-8061-d022b7528469@huawei.com> (raw)
In-Reply-To: <mk6bvhdvbeo5ey7oxlclkgya4ywk3izi4p2anl5n7a7zngneoj@qddrf2si5nfd>
On 2024/4/26 12:04, Kent Overstreet wrote:
> On Fri, Apr 26, 2024 at 11:21:36AM +0800, Hongbo Li wrote:
>> When compiling the bcachefs-tools, the following compilation warning
>> is reported:
>> libbcachefs/six.c: In function ‘__do_six_trylock’:
>> libbcachefs/six.c:90:12: warning: ‘old’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>> 90 | if (!(old & SIX_LOCK_HELD_intent)) {
>> | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~
>>
>> This is also a false altert. Only when @type=SIX_LOCK_write and @try=false
>> are passed in __do_six_trylock, the second condition branch would enter
>> which does not initialize the @old variable. But six_set_owner will not
>> use @old if @type is not SIX_LOCK_intent. There should be nothing wrong
>> in logical too.
>>
>> Although the report itself is a false alert, we can elimate the unitialize
>> compilation warning by assigning @old in front.
>>
>> Fixes: 84a37cbf62e0 ("six locks: Wakeup now takes lock on behalf of waiter")
>> Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
>
> let's just delete the assertion - I don't like moving around reading the
> lock state for this.
ok, thank you, and I will keep "old = atomic_read(&lock->state);" in the
following else branch for next version.
>
>> ---
>> v2:
>> - Fix the error about reading lock->state introduced in v1.
>>
>> v1: https://lore.kernel.org/all/20240419074851.1583392-3-lihongbo22@huawei.com/T/#u
>> ---
>> ---
>> fs/bcachefs/six.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/bcachefs/six.c b/fs/bcachefs/six.c
>> index 3a494c5d1247..8bfd22a6f771 100644
>> --- a/fs/bcachefs/six.c
>> +++ b/fs/bcachefs/six.c
>> @@ -118,11 +118,11 @@ static int __do_six_trylock(struct six_lock *lock, enum six_lock_type type,
>> struct task_struct *task, bool try)
>> {
>> int ret;
>> - u32 old;
>> + u32 old = atomic_read(&lock->state);
>>
>> EBUG_ON(type == SIX_LOCK_write && lock->owner != task);
>> EBUG_ON(type == SIX_LOCK_write &&
>> - (try != !(atomic_read(&lock->state) & SIX_LOCK_HELD_write)));
>> + (try != !(old & SIX_LOCK_HELD_write)));
>>
>> /*
>> * Percpu reader mode:
>> @@ -182,7 +182,6 @@ static int __do_six_trylock(struct six_lock *lock, enum six_lock_type type,
>> ret = -1 - SIX_LOCK_read;
>> }
>> } else {
>> - old = atomic_read(&lock->state);
>> do {
>> ret = !(old & l[type].lock_fail);
>> if (!ret || (type == SIX_LOCK_write && !try)) {
>> --
>> 2.34.1
>>
>
prev parent reply other threads:[~2024-04-26 6:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 3:21 [PATCH v2 0/2] eliminate the uninitialized compilation warning Hongbo Li
2024-04-26 3:21 ` [PATCH v2 1/2] bcachefs: eliminate the uninitialized compilation warning in bch2_reconstruct_snapshots Hongbo Li
2024-04-26 4:04 ` Kent Overstreet
2024-04-26 3:21 ` [PATCH v2 2/2] bcachefs: eliminate the uninitialized compilation warning in __do_six_trylock Hongbo Li
2024-04-26 4:04 ` Kent Overstreet
2024-04-26 6:09 ` Hongbo Li [this message]
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