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Fix potential memory leak of tev->e_list by reordering list_add before epoll_ctl #66

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@jkchen1095 jkchen1095 commented Aug 10, 2024

This commit addresses a potential memory leak in tgt_event_add related to
tev->e_list. Previously, epoll_ctl(EPOLL_CTL_ADD) was called before
list_add. This sequence could lead to a race condition where the epoll event
is registered and immediately triggered, leading to EPOLL_CTL_DEL and
list_del being called before list_add, resulting in the event being removed
from epoll but never added to the list, causing a memory leak after calling
list_add (Because no one will call list_del to remove this tev->e_list anymore).

To prevent this, list_add is now called before epoll_ctl(EPOLL_CTL_ADD).
This ensures that the tev->e_list is added to the list before any
epoll events can be triggered, allowing proper cleanup by list_del in case
of an early EPOLL_CTL_DEL.

@jkchen1095 jkchen1095 force-pushed the master branch 4 times, most recently from 1ccb178 to e84dc5d Compare August 10, 2024 13:45
@jkchen1095 jkchen1095 changed the title Fix potential memory leak of event_data->e_list by reordering list_add before epoll_ctl Fix potential memory leak of tev->e_list by reordering list_add before epoll_ctl Aug 10, 2024
@jkchen1095 jkchen1095 force-pushed the master branch 5 times, most recently from a2f404a to 8a41c08 Compare August 10, 2024 14:36
…e epoll_ctl

This commit addresses a potential memory leak in tgt_event_add related to
tev->e_list. Previously, epoll_ctl(EPOLL_CTL_ADD) was called before
list_add. This sequence could lead to a race condition where the epoll event
is registered and immediately triggered, leading to EPOLL_CTL_DEL and
list_del being called before list_add, resulting in the event being removed
from epoll but never added to the list, causing a memory leak after calling
list_add (Because no one will call list_del to remove this tev->e_list anymore).

To prevent this, list_add is now called before epoll_ctl(EPOLL_CTL_ADD).
This ensures that the tev->e_list is added to the list before any
epoll events can be triggered, allowing proper cleanup by list_del in case
of an early EPOLL_CTL_DEL.

Signed-off-by: JK Chen <jk.chen1095@gmail.com>
@fujita
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fujita commented Aug 14, 2024

One thread calls tgt_event_add() and another thread calls tgt_event_del()? It's possible?

@jkchen1095
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jkchen1095 commented Aug 14, 2024

Hi fujita
You are correct; in the context of a single thread, it indeed does not need to be considered. This fix is merely a formality in terms of standardization, and as long as there are no changes to a multi-threaded environment in the future, this issue will not actually arise.

@fujita
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fujita commented Aug 14, 2024

If we need to think about multi threads, there are many other races. So I don't think that fixing one place makes sense.

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2 participants