From: "Yordan Karadzhov (VMware)" <y.karadz@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH v2 2/3] kernel-shark: Fix potential memory leak in libkshark-collection
Date: Thu, 28 Nov 2019 11:25:33 +0200 [thread overview]
Message-ID: <61ba76fd-25ba-821d-b8e8-0f3209f692b5@gmail.com> (raw)
In-Reply-To: <20191127135416.6bcc0fd9@gandalf.local.home>
On 27.11.19 г. 20:54 ч., Steven Rostedt wrote:
> On Wed, 23 Oct 2019 15:21:44 +0300
> "Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:
>
>> When searching for the entry, do not loop over the original list of
>> requests. Use a copy instead. If we loop over the original list and
>> no entry is found in the first element of the list, later the memory
>> used for this first element will leak.
>>
>> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
>> ---
>> kernel-shark/src/libkshark-collection.c | 14 ++++++--------
>> 1 file changed, 6 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel-shark/src/libkshark-collection.c b/kernel-shark/src/libkshark-collection.c
>> index 02a014e..95fdbab 100644
>> --- a/kernel-shark/src/libkshark-collection.c
>> +++ b/kernel-shark/src/libkshark-collection.c
>> @@ -622,6 +622,7 @@ kshark_get_collection_entry_front(struct kshark_entry_request **req,
>> ssize_t *index)
>> {
>> const struct kshark_entry *entry = NULL;
>> + struct kshark_entry_request *list;
>
> Hi Yordan,
>
> I was looking at this patch in more detail, and I'm thinking that we
> don't need to pass in the address of the req pointer, but just the req
> pointer itself. The only place that I see the req pointer being
> modified is the failure case in map_collection_request_init() where it
> does:
>
> kshark_free_entry_request(*req);
> *req = NULL;
>
> But all callers do that free anyway.
>
Yes, because the caller is expected to do
kshark_free_entry_request(*req) at the end, here we have to set the
original pointer to NULL. Otherwise we will get double free error.
I think this is what I have been trying to fix, when I introduced the
memory leak.
And yes, I agree with you that carrying the address of the pointer
through all these functions is a bit ugly.
Thanks!
Yordan
> Maybe I'm missing something, but why are we passing in the pointer to
> the pointer of req, and not just the req pointer itself? I don't see a
> need to modify the pointer.
>
> Before this patch, *req is modified, but after this patch, it is not.
> If you pass in just "struct kshark_entry_request *req" then you don't
> even need to have the "list" variable, you could just use "req" because
> that would be a copy of the pointer.
>
> -- Steve
>
>
>
>> int req_count;
>>
>> /*
>> @@ -638,12 +639,10 @@ kshark_get_collection_entry_front(struct kshark_entry_request **req,
>> * Loop over the list of redefined requests and search until you find
>> * the first matching entry.
>> */
>> - while (*req) {
>> - entry = kshark_get_entry_front(*req, data, index);
>> + for (list = *req; list; list = list->next) {
>> + entry = kshark_get_entry_front(list, data, index);
>> if (entry)
>> break;
>> -
>> - *req = (*req)->next;
>> }
>>
>> return entry;
>> @@ -680,6 +679,7 @@ kshark_get_collection_entry_back(struct kshark_entry_request **req,
>> ssize_t *index)
>> {
>> const struct kshark_entry *entry = NULL;
>> + struct kshark_entry_request *list;
>> int req_count;
>>
>> /*
>> @@ -695,12 +695,10 @@ kshark_get_collection_entry_back(struct kshark_entry_request **req,
>> * Loop over the list of redefined requests and search until you find
>> * the first matching entry.
>> */
>> - while (*req) {
>> - entry = kshark_get_entry_back(*req, data, index);
>> + for (list = *req; list; list = list->next) {
>> + entry = kshark_get_entry_back(list, data, index);
>> if (entry)
>> break;
>> -
>> - *req = (*req)->next;
>> }
>>
>> return entry;
>
next prev parent reply other threads:[~2019-11-28 9:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-23 12:21 [PATCH v2 1/3] kernel-shark: Fix simple typo in the "File" menu Yordan Karadzhov (VMware)
2019-10-23 12:21 ` [PATCH v2 2/3] kernel-shark: Fix potential memory leak in libkshark-collection Yordan Karadzhov (VMware)
2019-11-27 18:54 ` Steven Rostedt
2019-11-28 9:25 ` Yordan Karadzhov (VMware) [this message]
2019-10-23 12:21 ` [PATCH v2 3/3] kernel-shark: When running as Root save all config settings in /root/ Yordan Karadzhov (VMware)
2019-11-27 20:13 ` Steven Rostedt
2019-11-28 11:29 ` Yordan Karadzhov (VMware)
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