ep_events_available() checks for available events by looking at ep->rdllist
and ep->ovflist. However, this is done without a lock, therefore the
returned value is not reliable. Because it is possible that both checks on
ep->rdllist and ep->ovflist are false while ep_start_scan() or
ep_done_scan() is being executed on other CPUs, despite events are
available.
This bug can be observed by:
1. Create an eventpoll with at least one ready level-triggered event
2. Create multiple threads who do epoll_wait() with zero timeout. The
threads do not consume the events, therefore all epoll_wait() should
return at least one event.
If one thread is executing ep_events_available() while another thread is
executing ep_start_scan() or ep_done_scan(), epoll_wait() may wrongly
return no event for the former thread.
This reproducer is implemented as TEST(epoll65) in
tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
Fix it by skipping ep_events_available(), just call ep_try_send_events()
directly.
epoll_sendevents() (io_uring) suffers the same problem, fix that as well.
There is still ep_busy_loop() who uses ep_events_available() without lock,
but it is probably okay (?) for busy-polling.
Fixes: c5a282e9635e ("fs/epoll: reduce the scope of wq lock in epoll_wait()")
Fixes: e59d3c64cba6 ("epoll: eliminate unnecessary lock for zero timeout")
Fixes: ae3a4f1fdc2c ("eventpoll: add epoll_sendevents() helper")
Signed-off-by: Nam Cao <namcao(a)linutronix.de>
Cc: stable(a)vger.kernel.org
---
fs/eventpoll.c | 16 ++--------------
1 file changed, 2 insertions(+), 14 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 0fbf5dfedb24..541481eafc20 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2022,7 +2022,7 @@ static int ep_schedule_timeout(ktime_t *to)
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, struct timespec64 *timeout)
{
- int res, eavail, timed_out = 0;
+ int res, eavail = 1, timed_out = 0;
u64 slack = 0;
wait_queue_entry_t wait;
ktime_t expires, *to = NULL;
@@ -2041,16 +2041,6 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
timed_out = 1;
}
- /*
- * This call is racy: We may or may not see events that are being added
- * to the ready list under the lock (e.g., in IRQ callbacks). For cases
- * with a non-zero timeout, this thread will check the ready list under
- * lock and will add to the wait queue. For cases with a zero
- * timeout, the user by definition should not care and will have to
- * recheck again.
- */
- eavail = ep_events_available(ep);
-
while (1) {
if (eavail) {
res = ep_try_send_events(ep, events, maxevents);
@@ -2496,9 +2486,7 @@ int epoll_sendevents(struct file *file, struct epoll_event __user *events,
* Racy call, but that's ok - it should get retried based on
* poll readiness anyway.
*/
- if (ep_events_available(ep))
- return ep_try_send_events(ep, events, maxevents);
- return 0;
+ return ep_try_send_events(ep, events, maxevents);
}
/*
--
2.39.5
Make sure we return the right pud value and not a value that could
have been overwritten in between by a different core.
Fixes: c3cc2a4a3a23 ("riscv: Add support for PUD THP")
Cc: stable(a)vger.kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti(a)rivosinc.com>
---
Note that this will conflict with
https://lore.kernel.org/linux-riscv/20250625063753.77511-1-ajd@linux.ibm.co…
if applied after 6.17.
---
arch/riscv/include/asm/pgtable.h | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 91697fbf1f9013005800f713797e4b6b1fc8d312..e69346307e78608dd98d8b7a77b7063c333448ee 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -942,6 +942,17 @@ static inline int pudp_test_and_clear_young(struct vm_area_struct *vma,
return ptep_test_and_clear_young(vma, address, (pte_t *)pudp);
}
+#define __HAVE_ARCH_PUDP_HUGE_GET_AND_CLEAR
+static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm,
+ unsigned long address, pud_t *pudp)
+{
+ pud_t pud = __pud(atomic_long_xchg((atomic_long_t *)pudp, 0));
+
+ page_table_check_pud_clear(mm, pud);
+
+ return pud;
+}
+
static inline int pud_young(pud_t pud)
{
return pte_young(pud_pte(pud));
---
base-commit: 62950c35a515743739e3d863eac25c20a5bd1613
change-id: 20250814-dev-alex-thp_pud_xchg-8153c313d946
Best regards,
--
Alexandre Ghiti <alexghiti(a)rivosinc.com>
Hi Sasha,
Thank you for maintaining the stable versions with Greg!
If I remember well, you run some scripts on your side to maintain the
queue/* branches in the linux-stable-rc Git tree [1], is that correct?
These branches have not been updated for a bit more than 3 weeks. Is it
normal?
Personally, I find them useful. But if it is just me, I can work without
them.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/…
Cheers,
Matt
--
Sponsored by the NGI0 Core fund.