The branch main has been updated by hselasky:
URL:
https://cgit.FreeBSD.org/src/commit/?id=b764a426534f2f5f86d6625288c74dafdbc94d2b
commit b764a426534f2f5f86d6625288c74dafdbc94d2b
Author: Hans Petter Selasky <hsela...@freebsd.org>
AuthorDate: 2021-05-21 11:17:42 +0000
Commit: Hans Petter Selasky <hsela...@freebsd.org>
CommitDate: 2021-05-21 11:18:41 +0000
There is a window where threads are removed from the process list and where
the thread destructor is invoked. Catch that window by waiting for all
task_struct allocations to be returned before freeing the UMA zone in the
LinuxKPI. Else UMA may fail to release the zone due to concurrent access
and panic:
panic() - Bad link element prev->next != elm
zone_release()
bucket_drain()
bucket_free()
zone_dtor()
zone_free_item()
uma_zdestroy()
linux_current_uninit()
This failure can be triggered by loading and unloading the LinuxKPI module
in a loop:
while true
do
kldload linuxkpi
kldunload linuxkpi
done
Discussed with: kib@
MFC after: 1 week
Sponsored by: Mellanox Technologies // NVIDIA Networking
---
sys/compat/linuxkpi/common/src/linux_current.c | 35 ++++++++++++++++++++++----
1 file changed, 30 insertions(+), 5 deletions(-)
diff --git a/sys/compat/linuxkpi/common/src/linux_current.c
b/sys/compat/linuxkpi/common/src/linux_current.c
index 9bae7ee92e49..51e396081c04 100644
--- a/sys/compat/linuxkpi/common/src/linux_current.c
+++ b/sys/compat/linuxkpi/common/src/linux_current.c
@@ -45,6 +45,7 @@ extern u_int first_msi_irq, num_msi_irqs;
static eventhandler_tag linuxkpi_thread_dtor_tag;
+static atomic_t linux_current_allocs;
static uma_zone_t linux_current_zone;
static uma_zone_t linux_mm_zone;
@@ -146,6 +147,10 @@ linux_alloc_current(struct thread *td, int flags)
/* free mm_struct pointer, if any */
uma_zfree(linux_mm_zone, mm);
+ /* keep track of number of allocations */
+ if (atomic_add_return(1, &linux_current_allocs) == INT_MAX)
+ panic("linux_alloc_current: Refcount too high!");
+
return (0);
}
@@ -173,6 +178,10 @@ linux_free_current(struct task_struct *ts)
{
mmput(ts->mm);
uma_zfree(linux_current_zone, ts);
+
+ /* keep track of number of allocations */
+ if (atomic_sub_return(1, &linux_current_allocs) < 0)
+ panic("linux_free_current: Negative refcount!");
}
static void
@@ -271,10 +280,6 @@ SYSCTL_INT(_compat_linuxkpi, OID_AUTO, task_struct_reserve,
static void
linux_current_init(void *arg __unused)
{
- lkpi_alloc_current = linux_alloc_current;
- linuxkpi_thread_dtor_tag = EVENTHANDLER_REGISTER(thread_dtor,
- linuxkpi_thread_dtor, NULL, EVENTHANDLER_PRI_ANY);
-
TUNABLE_INT_FETCH("compat.linuxkpi.task_struct_reserve",
&lkpi_task_resrv);
if (lkpi_task_resrv == 0) {
@@ -298,6 +303,12 @@ linux_current_init(void *arg __unused)
UMA_ALIGN_PTR, 0);
uma_zone_reserve(linux_mm_zone, lkpi_task_resrv);
uma_prealloc(linux_mm_zone, lkpi_task_resrv);
+
+ atomic_thread_fence_seq_cst();
+
+ lkpi_alloc_current = linux_alloc_current;
+ linuxkpi_thread_dtor_tag = EVENTHANDLER_REGISTER(thread_dtor,
+ linuxkpi_thread_dtor, NULL, EVENTHANDLER_PRI_ANY);
}
SYSINIT(linux_current, SI_SUB_EVENTHANDLER, SI_ORDER_SECOND,
linux_current_init, NULL);
@@ -309,6 +320,10 @@ linux_current_uninit(void *arg __unused)
struct task_struct *ts;
struct thread *td;
+ lkpi_alloc_current = linux_alloc_current_noop;
+
+ atomic_thread_fence_seq_cst();
+
sx_slock(&allproc_lock);
FOREACH_PROC_IN_SYSTEM(p) {
PROC_LOCK(p);
@@ -321,8 +336,18 @@ linux_current_uninit(void *arg __unused)
PROC_UNLOCK(p);
}
sx_sunlock(&allproc_lock);
+
+ /*
+ * There is a window where threads are removed from the
+ * process list and where the thread destructor is invoked.
+ * Catch that window by waiting for all task_struct
+ * allocations to be returned before freeing the UMA zone.
+ */
+ while (atomic_read(&linux_current_allocs) != 0)
+ pause("W", 1);
+
EVENTHANDLER_DEREGISTER(thread_dtor, linuxkpi_thread_dtor_tag);
- lkpi_alloc_current = linux_alloc_current_noop;
+
uma_zdestroy(linux_current_zone);
uma_zdestroy(linux_mm_zone);
}
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