As the clone side already executes pid allocation with only pidmap_lock
held, issuing free_pid() while still holding tasklist_lock exacerbates
total hold time of the latter.

The pid array is smuggled through newly added release_task_post struct
so that any extra things want to get moved out have means to do it.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 include/linux/pid.h |  7 ++++---
 kernel/exit.c       | 27 +++++++++++++++++++--------
 kernel/pid.c        | 44 ++++++++++++++++++++++----------------------
 kernel/sys.c        | 14 +++++++++-----
 4 files changed, 54 insertions(+), 38 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 98837a1ff0f3..311ecebd7d56 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -101,9 +101,9 @@ extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
  * these helpers must be called with the tasklist_lock write-held.
  */
 extern void attach_pid(struct task_struct *task, enum pid_type);
-extern void detach_pid(struct task_struct *task, enum pid_type);
-extern void change_pid(struct task_struct *task, enum pid_type,
-			struct pid *pid);
+void detach_pid(struct pid **pids, struct task_struct *task, enum pid_type);
+void change_pid(struct pid **pids, struct task_struct *task, enum pid_type,
+		struct pid *pid);
 extern void exchange_tids(struct task_struct *task, struct task_struct *old);
 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
 			 enum pid_type);
@@ -129,6 +129,7 @@ extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 			     size_t set_tid_size);
 extern void free_pid(struct pid *pid);
+void free_pids(struct pid **pids);
 extern void disable_pid_allocation(struct pid_namespace *ns);
 
 /*
diff --git a/kernel/exit.c b/kernel/exit.c
index b5c0cbc6bdfb..0d6df671c8a8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -122,14 +122,22 @@ static __init int kernel_exit_sysfs_init(void)
 late_initcall(kernel_exit_sysfs_init);
 #endif
 
-static void __unhash_process(struct task_struct *p, bool group_dead)
+/*
+ * For things release_task() would like to do *after* tasklist_lock is released.
+ */
+struct release_task_post {
+	struct pid *pids[PIDTYPE_MAX];
+};
+
+static void __unhash_process(struct release_task_post *post, struct task_struct *p,
+			     bool group_dead)
 {
 	nr_threads--;
-	detach_pid(p, PIDTYPE_PID);
+	detach_pid(post->pids, p, PIDTYPE_PID);
 	if (group_dead) {
-		detach_pid(p, PIDTYPE_TGID);
-		detach_pid(p, PIDTYPE_PGID);
-		detach_pid(p, PIDTYPE_SID);
+		detach_pid(post->pids, p, PIDTYPE_TGID);
+		detach_pid(post->pids, p, PIDTYPE_PGID);
+		detach_pid(post->pids, p, PIDTYPE_SID);
 
 		list_del_rcu(&p->tasks);
 		list_del_init(&p->sibling);
@@ -141,7 +149,7 @@ static void __unhash_process(struct task_struct *p, bool group_dead)
 /*
  * This function expects the tasklist_lock write-locked.
  */
-static void __exit_signal(struct task_struct *tsk)
+static void __exit_signal(struct release_task_post *post, struct task_struct *tsk)
 {
 	struct signal_struct *sig = tsk->signal;
 	bool group_dead = thread_group_leader(tsk);
@@ -194,7 +202,7 @@ static void __exit_signal(struct task_struct *tsk)
 	task_io_accounting_add(&sig->ioac, &tsk->ioac);
 	sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
 	sig->nr_threads--;
-	__unhash_process(tsk, group_dead);
+	__unhash_process(post, tsk, group_dead);
 	write_sequnlock(&sig->stats_lock);
 
 	/*
@@ -236,10 +244,13 @@ void __weak release_thread(struct task_struct *dead_task)
 
 void release_task(struct task_struct *p)
 {
+	struct release_task_post post;
 	struct task_struct *leader;
 	struct pid *thread_pid;
 	int zap_leader;
 repeat:
+	memset(&post, 0, sizeof(post));
+
 	/* don't need to get the RCU readlock here - the process is dead and
 	 * can't be modifying its own credentials. But shut RCU-lockdep up */
 	rcu_read_lock();
@@ -252,7 +263,7 @@ void release_task(struct task_struct *p)
 
 	write_lock_irq(&tasklist_lock);
 	ptrace_release_task(p);
-	__exit_signal(p);
+	__exit_signal(&post, p);
 
 	/*
 	 * If we are the last non-leader member of the thread
diff --git a/kernel/pid.c b/kernel/pid.c
index 2ae872f689a7..73625f28c166 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -88,20 +88,6 @@ struct pid_namespace init_pid_ns = {
 };
 EXPORT_SYMBOL_GPL(init_pid_ns);
 
-/*
- * Note: disable interrupts while the pidmap_lock is held as an
- * interrupt might come in and do read_lock(&tasklist_lock).
- *
- * If we don't disable interrupts there is a nasty deadlock between
- * detach_pid()->free_pid() and another cpu that does
- * spin_lock(&pidmap_lock) followed by an interrupt routine that does
- * read_lock(&tasklist_lock);
- *
- * After we clean up the tasklist_lock and know there are no
- * irq handlers that take it we can leave the interrupts enabled.
- * For now it is easier to be safe than to prove it can't happen.
- */
-
 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
 seqcount_spinlock_t pidmap_lock_seq = SEQCNT_SPINLOCK_ZERO(pidmap_lock_seq, &pidmap_lock);
 
@@ -128,10 +114,11 @@ static void delayed_put_pid(struct rcu_head *rhp)
 
 void free_pid(struct pid *pid)
 {
-	/* We can be called with write_lock_irq(&tasklist_lock) held */
 	int i;
 	unsigned long flags;
 
+	lockdep_assert_not_held(&tasklist_lock);
+
 	spin_lock_irqsave(&pidmap_lock, flags);
 	for (i = 0; i <= pid->level; i++) {
 		struct upid *upid = pid->numbers + i;
@@ -160,6 +147,18 @@ void free_pid(struct pid *pid)
 	call_rcu(&pid->rcu, delayed_put_pid);
 }
 
+void free_pids(struct pid **pids)
+{
+	int tmp;
+
+	/*
+	 * This can batch pidmap_lock.
+	 */
+	for (tmp = PIDTYPE_MAX; --tmp >= 0; )
+		if (pids[tmp])
+			free_pid(pids[tmp]);
+}
+
 struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 		      size_t set_tid_size)
 {
@@ -347,8 +346,8 @@ void attach_pid(struct task_struct *task, enum pid_type type)
 	hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
 }
 
-static void __change_pid(struct task_struct *task, enum pid_type type,
-			struct pid *new)
+static void __change_pid(struct pid **pids, struct task_struct *task,
+			 enum pid_type type, struct pid *new)
 {
 	struct pid **pid_ptr, *pid;
 	int tmp;
@@ -370,18 +369,19 @@ static void __change_pid(struct task_struct *task, enum pid_type type,
 		if (pid_has_task(pid, tmp))
 			return;
 
-	free_pid(pid);
+	WARN_ON(pids[type]);
+	pids[type] = pid;
 }
 
-void detach_pid(struct task_struct *task, enum pid_type type)
+void detach_pid(struct pid **pids, struct task_struct *task, enum pid_type type)
 {
-	__change_pid(task, type, NULL);
+	__change_pid(pids, task, type, NULL);
 }
 
-void change_pid(struct task_struct *task, enum pid_type type,
+void change_pid(struct pid **pids, struct task_struct *task, enum pid_type type,
 		struct pid *pid)
 {
-	__change_pid(task, type, pid);
+	__change_pid(pids, task, type, pid);
 	attach_pid(task, type);
 }
 
diff --git a/kernel/sys.c b/kernel/sys.c
index cb366ff8703a..4efca8a97d62 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1085,6 +1085,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
 {
 	struct task_struct *p;
 	struct task_struct *group_leader = current->group_leader;
+	struct pid *pids[PIDTYPE_MAX] = { 0 };
 	struct pid *pgrp;
 	int err;
 
@@ -1142,13 +1143,14 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
 		goto out;
 
 	if (task_pgrp(p) != pgrp)
-		change_pid(p, PIDTYPE_PGID, pgrp);
+		change_pid(pids, p, PIDTYPE_PGID, pgrp);
 
 	err = 0;
 out:
 	/* All paths lead to here, thus we are safe. -DaveM */
 	write_unlock_irq(&tasklist_lock);
 	rcu_read_unlock();
+	free_pids(pids);
 	return err;
 }
 
@@ -1222,21 +1224,22 @@ SYSCALL_DEFINE1(getsid, pid_t, pid)
 	return retval;
 }
 
-static void set_special_pids(struct pid *pid)
+static void set_special_pids(struct pid **pids, struct pid *pid)
 {
 	struct task_struct *curr = current->group_leader;
 
 	if (task_session(curr) != pid)
-		change_pid(curr, PIDTYPE_SID, pid);
+		change_pid(pids, curr, PIDTYPE_SID, pid);
 
 	if (task_pgrp(curr) != pid)
-		change_pid(curr, PIDTYPE_PGID, pid);
+		change_pid(pids, curr, PIDTYPE_PGID, pid);
 }
 
 int ksys_setsid(void)
 {
 	struct task_struct *group_leader = current->group_leader;
 	struct pid *sid = task_pid(group_leader);
+	struct pid *pids[PIDTYPE_MAX] = { 0 };
 	pid_t session = pid_vnr(sid);
 	int err = -EPERM;
 
@@ -1252,13 +1255,14 @@ int ksys_setsid(void)
 		goto out;
 
 	group_leader->signal->leader = 1;
-	set_special_pids(sid);
+	set_special_pids(pids, sid);
 
 	proc_clear_tty(group_leader);
 
 	err = session;
 out:
 	write_unlock_irq(&tasklist_lock);
+	free_pids(pids);
 	if (err > 0) {
 		proc_sid_connector(group_leader);
 		sched_autogroup_create_attach(group_leader);
-- 
2.43.0

On Wed, Feb 05, 2025 at 09:09:28PM +0100, Mateusz Guzik wrote:
> As the clone side already executes pid allocation with only pidmap_lock
> held, issuing free_pid() while still holding tasklist_lock exacerbates
> total hold time of the latter.
> 
> The pid array is smuggled through newly added release_task_post struct
> so that any extra things want to get moved out have means to do it.

We are seeing failures in -next with the clone3 clone3_set_tid selftest
on at least arm and arm64 systems which have been bisected to this
commit, in -next as 88dec855ce117f52bcf88748ddcbb25b10f4f2fc (same
bisect for both):

For arm64 we're seeing a bunch of new failures including:

# # [389] Trying clone3() with CLONE_SET_TID to 391 and 0x0
# # File exists - Failed to create new process
# # [389] clone3() with CLONE_SET_TID 391 says: -17 - expected 0
# not ok 19 reallocate child TID with 1 TIDs and flags 0x0

# # [389] Trying clone3() with CLONE_SET_TID to 1 and 0x20000000
# # File exists - Failed to create new process
# # [389] clone3() with CLONE_SET_TID 1 says: -17 - expected 0
# not ok 21 create PID 1 in new NS with 2 TIDs and flags 0x20000000

# # [1] Trying clone3() with CLONE_SET_TID to 43 and 0x0
# # File exists - Failed to create new process
# # [1] clone3() with CLONE_SET_TID 43 says: -17 - expected 0
# not ok 24 check leak on invalid specific TID with 2 TIDs and flags 0x0

but there's more, 32 bit only seems to see one new failure (at least on
Beaglebone Black which is where I have that test running).

Full log for a run on arm64:

   https://lava.sirena.org.uk/scheduler/job/1102114

and arm:

   https://lava.sirena.org.uk/scheduler/job/1102088

Bisect log, the start is my tooling feeding in test results it already
has to hand in the commit range to seed the bisect:

# bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
# good: [653cd79f296fc6fa592cb9fa2f7b8494d5573a43] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
# good: [4c7518062d638837cea915e0ffe30f846780639a] ASoC: SOF: ipc4: Add support for split firmware releases
# good: [0a7c85b516830c0bb088b0bdb2f2c50c76fc531a] regulator: ad5398: Fix incorrect power down bit mask
# good: [215705db51eb23052c73126d2efb6acbc2db0424] spi: Replace custom fsleep() implementation
# good: [6603c5133daadbb3277fbd93be0d0d5b8ec928e8] ASoC: dt-bindings: atmel,at91-ssc: Convert to YAML format
# good: [25fac20edd09b60651eabcc57c187b1277f43d08] spi: gpio: Support a single always-selected device
# good: [652ffad172d089acb1a20e5fde1b66e687832b06] spi: fsi: Batch TX operations
# good: [6eab7034579917f207ca6d8e3f4e11e85e0ab7d5] ASoC: soc-core: Stop using of_property_read_bool() for non-boolean properties
# good: [f5aab0438ef17f01c5ecd25e61ae6a03f82a4586] regulator: pca9450: Fix enable register for LDO5
# good: [c1ac98492d1584d31f335d233a5cd7a4d4116e5a] spi: realtek-rtl-snand: Drop unneeded assignment for cache_type
# good: [5a6a461079decea452fdcae955bccecf92e07e97] regulator: ad5398: Add device tree support
# good: [995cf0e014b0144edf1125668a97c252c5ab775e] regmap: Reorder 'struct regmap'
# good: [89785306453ce6d949e783f6936821a0b7649ee2] spi: zynqmp-gqspi: Always acknowledge interrupts
# good: [0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d] Merge branch 'for-5.19/cleanup' into for-next
git bisect start 'ed58d103e6da15a442ff87567898768dc3a66987' '653cd79f296fc6fa592cb9fa2f7b8494d5573a43' '4c7518062d638837cea915e0ffe30f846780639a' '0a7c85b516830c0bb088b0bdb2f2c50c76fc531a' '215705db51eb23052c73126d2efb6acbc2db0424' '6603c5133daadbb3277fbd93be0d0d5b8ec928e8' '25fac20edd09b60651eabcc57c187b1277f43d08' '652ffad172d089acb1a20e5fde1b66e687832b06' '6eab7034579917f207ca6d8e3f4e11e85e0ab7d5' 'f5aab0438ef17f01c5ecd25e61ae6a03f82a4586' 'c1ac98492d1584d31f335d233a5cd7a4d4116e5a' '5a6a461079decea452fdcae955bccecf92e07e97' '995cf0e014b0144edf1125668a97c252c5ab775e' '89785306453ce6d949e783f6936821a0b7649ee2' '0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d'
# bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
git bisect bad ed58d103e6da15a442ff87567898768dc3a66987
# bad: [5a44f71c6ba5b0a7623c25047ac61ed852afbd84] Merge branch 'for-linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git
git bisect bad 5a44f71c6ba5b0a7623c25047ac61ed852afbd84
# bad: [953e43d94b2048d260774e9ddbfd3f378aa2c256] Merge branch 'fs-next' of linux-next
git bisect bad 953e43d94b2048d260774e9ddbfd3f378aa2c256
# good: [2ab7baf7ebddff9faff6846648fd0753e5ee58c1] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux.git
git bisect good 2ab7baf7ebddff9faff6846648fd0753e5ee58c1
# good: [09c7fd0d4465df7fd6cda5668bd32267884b6cbf] Merge branch '9p-next' of git://github.com/martinetd/linux
git bisect good 09c7fd0d4465df7fd6cda5668bd32267884b6cbf
# bad: [7a1f00b09c09aadbf33660a31f3f3d8ee6302c45] Merge branch 'vfs-6.15.iomap' into vfs.all
git bisect bad 7a1f00b09c09aadbf33660a31f3f3d8ee6302c45
# good: [9bc19073026d0dce6b7d17d22e74643c80283f8f] Merge branch 'vfs-6.15.mount' into vfs.all
git bisect good 9bc19073026d0dce6b7d17d22e74643c80283f8f
# bad: [ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c] Merge branch 'kernel-6.15.tasklist_lock' into vfs.all
git bisect bad ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c
# good: [d7c340391cb0f0882bc8d5d9798ef32b577a89bc] Merge branch 'vfs-6.15.pipe' into vfs.all
git bisect good d7c340391cb0f0882bc8d5d9798ef32b577a89bc
# good: [e88fed94388f62a28acfef4954348abe79557d19] pid: sprinkle tasklist_lock asserts
git bisect good e88fed94388f62a28acfef4954348abe79557d19
# bad: [5ca27e0557d722dd648f949dde6e4997f6255f18] pid: drop irq disablement around pidmap_lock
git bisect bad 5ca27e0557d722dd648f949dde6e4997f6255f18
# bad: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock
git bisect bad 88dec855ce117f52bcf88748ddcbb25b10f4f2fc
# first bad commit: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock

... and found

next-20250207 is somehow missing a call to free_pids() in release_task().

There was some fat-fingering in v5 and maybe previous versions which
made the call land in the wrong commit, I presume there was further
crappery elsewhere which concluded in the call not being present to
begin with.

I just confirmed the version is is intended to land has the call in
the right place:
https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=kernel-6.15.tasklist_lock&id=7903f907a226058ed99f86e9924e082aea57fc45

As in this chunk fell out in -next:
diff --git a/kernel/exit.c b/kernel/exit.c
index b4fc3cc96ea4..0d6df671c8a8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -289,6 +289,7 @@ void release_task(struct task_struct *p)
        put_pid(thread_pid);
        add_device_randomness(&p->se.sum_exec_runtime,
                              sizeof(p->se.sum_exec_runtime));
+       free_pids(post.pids);
        release_thread(p);
        put_task_struct_rcu_user(p);

On Fri, Feb 7, 2025 at 7:31 PM Mark Brown <broonie@kernel.org> wrote:
>
> On Wed, Feb 05, 2025 at 09:09:28PM +0100, Mateusz Guzik wrote:
> > As the clone side already executes pid allocation with only pidmap_lock
> > held, issuing free_pid() while still holding tasklist_lock exacerbates
> > total hold time of the latter.
> >
> > The pid array is smuggled through newly added release_task_post struct
> > so that any extra things want to get moved out have means to do it.
>
> We are seeing failures in -next with the clone3 clone3_set_tid selftest
> on at least arm and arm64 systems which have been bisected to this
> commit, in -next as 88dec855ce117f52bcf88748ddcbb25b10f4f2fc (same
> bisect for both):
>
> For arm64 we're seeing a bunch of new failures including:
>
> # # [389] Trying clone3() with CLONE_SET_TID to 391 and 0x0
> # # File exists - Failed to create new process
> # # [389] clone3() with CLONE_SET_TID 391 says: -17 - expected 0
> # not ok 19 reallocate child TID with 1 TIDs and flags 0x0
>
> # # [389] Trying clone3() with CLONE_SET_TID to 1 and 0x20000000
> # # File exists - Failed to create new process
> # # [389] clone3() with CLONE_SET_TID 1 says: -17 - expected 0
> # not ok 21 create PID 1 in new NS with 2 TIDs and flags 0x20000000
>
> # # [1] Trying clone3() with CLONE_SET_TID to 43 and 0x0
> # # File exists - Failed to create new process
> # # [1] clone3() with CLONE_SET_TID 43 says: -17 - expected 0
> # not ok 24 check leak on invalid specific TID with 2 TIDs and flags 0x0
>
> but there's more, 32 bit only seems to see one new failure (at least on
> Beaglebone Black which is where I have that test running).
>
> Full log for a run on arm64:
>
>    https://lava.sirena.org.uk/scheduler/job/1102114
>
> and arm:
>
>    https://lava.sirena.org.uk/scheduler/job/1102088
>
> Bisect log, the start is my tooling feeding in test results it already
> has to hand in the commit range to seed the bisect:
>
> # bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
> # good: [653cd79f296fc6fa592cb9fa2f7b8494d5573a43] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
> # good: [4c7518062d638837cea915e0ffe30f846780639a] ASoC: SOF: ipc4: Add support for split firmware releases
> # good: [0a7c85b516830c0bb088b0bdb2f2c50c76fc531a] regulator: ad5398: Fix incorrect power down bit mask
> # good: [215705db51eb23052c73126d2efb6acbc2db0424] spi: Replace custom fsleep() implementation
> # good: [6603c5133daadbb3277fbd93be0d0d5b8ec928e8] ASoC: dt-bindings: atmel,at91-ssc: Convert to YAML format
> # good: [25fac20edd09b60651eabcc57c187b1277f43d08] spi: gpio: Support a single always-selected device
> # good: [652ffad172d089acb1a20e5fde1b66e687832b06] spi: fsi: Batch TX operations
> # good: [6eab7034579917f207ca6d8e3f4e11e85e0ab7d5] ASoC: soc-core: Stop using of_property_read_bool() for non-boolean properties
> # good: [f5aab0438ef17f01c5ecd25e61ae6a03f82a4586] regulator: pca9450: Fix enable register for LDO5
> # good: [c1ac98492d1584d31f335d233a5cd7a4d4116e5a] spi: realtek-rtl-snand: Drop unneeded assignment for cache_type
> # good: [5a6a461079decea452fdcae955bccecf92e07e97] regulator: ad5398: Add device tree support
> # good: [995cf0e014b0144edf1125668a97c252c5ab775e] regmap: Reorder 'struct regmap'
> # good: [89785306453ce6d949e783f6936821a0b7649ee2] spi: zynqmp-gqspi: Always acknowledge interrupts
> # good: [0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d] Merge branch 'for-5.19/cleanup' into for-next
> git bisect start 'ed58d103e6da15a442ff87567898768dc3a66987' '653cd79f296fc6fa592cb9fa2f7b8494d5573a43' '4c7518062d638837cea915e0ffe30f846780639a' '0a7c85b516830c0bb088b0bdb2f2c50c76fc531a' '215705db51eb23052c73126d2efb6acbc2db0424' '6603c5133daadbb3277fbd93be0d0d5b8ec928e8' '25fac20edd09b60651eabcc57c187b1277f43d08' '652ffad172d089acb1a20e5fde1b66e687832b06' '6eab7034579917f207ca6d8e3f4e11e85e0ab7d5' 'f5aab0438ef17f01c5ecd25e61ae6a03f82a4586' 'c1ac98492d1584d31f335d233a5cd7a4d4116e5a' '5a6a461079decea452fdcae955bccecf92e07e97' '995cf0e014b0144edf1125668a97c252c5ab775e' '89785306453ce6d949e783f6936821a0b7649ee2' '0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d'
> # bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
> git bisect bad ed58d103e6da15a442ff87567898768dc3a66987
> # bad: [5a44f71c6ba5b0a7623c25047ac61ed852afbd84] Merge branch 'for-linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git
> git bisect bad 5a44f71c6ba5b0a7623c25047ac61ed852afbd84
> # bad: [953e43d94b2048d260774e9ddbfd3f378aa2c256] Merge branch 'fs-next' of linux-next
> git bisect bad 953e43d94b2048d260774e9ddbfd3f378aa2c256
> # good: [2ab7baf7ebddff9faff6846648fd0753e5ee58c1] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux.git
> git bisect good 2ab7baf7ebddff9faff6846648fd0753e5ee58c1
> # good: [09c7fd0d4465df7fd6cda5668bd32267884b6cbf] Merge branch '9p-next' of git://github.com/martinetd/linux
> git bisect good 09c7fd0d4465df7fd6cda5668bd32267884b6cbf
> # bad: [7a1f00b09c09aadbf33660a31f3f3d8ee6302c45] Merge branch 'vfs-6.15.iomap' into vfs.all
> git bisect bad 7a1f00b09c09aadbf33660a31f3f3d8ee6302c45
> # good: [9bc19073026d0dce6b7d17d22e74643c80283f8f] Merge branch 'vfs-6.15.mount' into vfs.all
> git bisect good 9bc19073026d0dce6b7d17d22e74643c80283f8f
> # bad: [ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c] Merge branch 'kernel-6.15.tasklist_lock' into vfs.all
> git bisect bad ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c
> # good: [d7c340391cb0f0882bc8d5d9798ef32b577a89bc] Merge branch 'vfs-6.15.pipe' into vfs.all
> git bisect good d7c340391cb0f0882bc8d5d9798ef32b577a89bc
> # good: [e88fed94388f62a28acfef4954348abe79557d19] pid: sprinkle tasklist_lock asserts
> git bisect good e88fed94388f62a28acfef4954348abe79557d19
> # bad: [5ca27e0557d722dd648f949dde6e4997f6255f18] pid: drop irq disablement around pidmap_lock
> git bisect bad 5ca27e0557d722dd648f949dde6e4997f6255f18
> # bad: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock
> git bisect bad 88dec855ce117f52bcf88748ddcbb25b10f4f2fc
> # first bad commit: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock



-- 
Mateusz Guzik <mjguzik gmail.com>

thanks for the report, i'll prod it over the weekend

On Fri, Feb 7, 2025 at 7:31 PM Mark Brown <broonie@kernel.org> wrote:
>
> On Wed, Feb 05, 2025 at 09:09:28PM +0100, Mateusz Guzik wrote:
> > As the clone side already executes pid allocation with only pidmap_lock
> > held, issuing free_pid() while still holding tasklist_lock exacerbates
> > total hold time of the latter.
> >
> > The pid array is smuggled through newly added release_task_post struct
> > so that any extra things want to get moved out have means to do it.
>
> We are seeing failures in -next with the clone3 clone3_set_tid selftest
> on at least arm and arm64 systems which have been bisected to this
> commit, in -next as 88dec855ce117f52bcf88748ddcbb25b10f4f2fc (same
> bisect for both):
>
> For arm64 we're seeing a bunch of new failures including:
>
> # # [389] Trying clone3() with CLONE_SET_TID to 391 and 0x0
> # # File exists - Failed to create new process
> # # [389] clone3() with CLONE_SET_TID 391 says: -17 - expected 0
> # not ok 19 reallocate child TID with 1 TIDs and flags 0x0
>
> # # [389] Trying clone3() with CLONE_SET_TID to 1 and 0x20000000
> # # File exists - Failed to create new process
> # # [389] clone3() with CLONE_SET_TID 1 says: -17 - expected 0
> # not ok 21 create PID 1 in new NS with 2 TIDs and flags 0x20000000
>
> # # [1] Trying clone3() with CLONE_SET_TID to 43 and 0x0
> # # File exists - Failed to create new process
> # # [1] clone3() with CLONE_SET_TID 43 says: -17 - expected 0
> # not ok 24 check leak on invalid specific TID with 2 TIDs and flags 0x0
>
> but there's more, 32 bit only seems to see one new failure (at least on
> Beaglebone Black which is where I have that test running).
>
> Full log for a run on arm64:
>
>    https://lava.sirena.org.uk/scheduler/job/1102114
>
> and arm:
>
>    https://lava.sirena.org.uk/scheduler/job/1102088
>
> Bisect log, the start is my tooling feeding in test results it already
> has to hand in the commit range to seed the bisect:
>
> # bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
> # good: [653cd79f296fc6fa592cb9fa2f7b8494d5573a43] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
> # good: [4c7518062d638837cea915e0ffe30f846780639a] ASoC: SOF: ipc4: Add support for split firmware releases
> # good: [0a7c85b516830c0bb088b0bdb2f2c50c76fc531a] regulator: ad5398: Fix incorrect power down bit mask
> # good: [215705db51eb23052c73126d2efb6acbc2db0424] spi: Replace custom fsleep() implementation
> # good: [6603c5133daadbb3277fbd93be0d0d5b8ec928e8] ASoC: dt-bindings: atmel,at91-ssc: Convert to YAML format
> # good: [25fac20edd09b60651eabcc57c187b1277f43d08] spi: gpio: Support a single always-selected device
> # good: [652ffad172d089acb1a20e5fde1b66e687832b06] spi: fsi: Batch TX operations
> # good: [6eab7034579917f207ca6d8e3f4e11e85e0ab7d5] ASoC: soc-core: Stop using of_property_read_bool() for non-boolean properties
> # good: [f5aab0438ef17f01c5ecd25e61ae6a03f82a4586] regulator: pca9450: Fix enable register for LDO5
> # good: [c1ac98492d1584d31f335d233a5cd7a4d4116e5a] spi: realtek-rtl-snand: Drop unneeded assignment for cache_type
> # good: [5a6a461079decea452fdcae955bccecf92e07e97] regulator: ad5398: Add device tree support
> # good: [995cf0e014b0144edf1125668a97c252c5ab775e] regmap: Reorder 'struct regmap'
> # good: [89785306453ce6d949e783f6936821a0b7649ee2] spi: zynqmp-gqspi: Always acknowledge interrupts
> # good: [0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d] Merge branch 'for-5.19/cleanup' into for-next
> git bisect start 'ed58d103e6da15a442ff87567898768dc3a66987' '653cd79f296fc6fa592cb9fa2f7b8494d5573a43' '4c7518062d638837cea915e0ffe30f846780639a' '0a7c85b516830c0bb088b0bdb2f2c50c76fc531a' '215705db51eb23052c73126d2efb6acbc2db0424' '6603c5133daadbb3277fbd93be0d0d5b8ec928e8' '25fac20edd09b60651eabcc57c187b1277f43d08' '652ffad172d089acb1a20e5fde1b66e687832b06' '6eab7034579917f207ca6d8e3f4e11e85e0ab7d5' 'f5aab0438ef17f01c5ecd25e61ae6a03f82a4586' 'c1ac98492d1584d31f335d233a5cd7a4d4116e5a' '5a6a461079decea452fdcae955bccecf92e07e97' '995cf0e014b0144edf1125668a97c252c5ab775e' '89785306453ce6d949e783f6936821a0b7649ee2' '0e11f2076e7fa3efa3e0a694bc4d30ef185f0f7d'
> # bad: [ed58d103e6da15a442ff87567898768dc3a66987] Add linux-next specific files for 20250207
> git bisect bad ed58d103e6da15a442ff87567898768dc3a66987
> # bad: [5a44f71c6ba5b0a7623c25047ac61ed852afbd84] Merge branch 'for-linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git
> git bisect bad 5a44f71c6ba5b0a7623c25047ac61ed852afbd84
> # bad: [953e43d94b2048d260774e9ddbfd3f378aa2c256] Merge branch 'fs-next' of linux-next
> git bisect bad 953e43d94b2048d260774e9ddbfd3f378aa2c256
> # good: [2ab7baf7ebddff9faff6846648fd0753e5ee58c1] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux.git
> git bisect good 2ab7baf7ebddff9faff6846648fd0753e5ee58c1
> # good: [09c7fd0d4465df7fd6cda5668bd32267884b6cbf] Merge branch '9p-next' of git://github.com/martinetd/linux
> git bisect good 09c7fd0d4465df7fd6cda5668bd32267884b6cbf
> # bad: [7a1f00b09c09aadbf33660a31f3f3d8ee6302c45] Merge branch 'vfs-6.15.iomap' into vfs.all
> git bisect bad 7a1f00b09c09aadbf33660a31f3f3d8ee6302c45
> # good: [9bc19073026d0dce6b7d17d22e74643c80283f8f] Merge branch 'vfs-6.15.mount' into vfs.all
> git bisect good 9bc19073026d0dce6b7d17d22e74643c80283f8f
> # bad: [ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c] Merge branch 'kernel-6.15.tasklist_lock' into vfs.all
> git bisect bad ba734a751d30f59e3b10d6792a1e1b50e7b1fc0c
> # good: [d7c340391cb0f0882bc8d5d9798ef32b577a89bc] Merge branch 'vfs-6.15.pipe' into vfs.all
> git bisect good d7c340391cb0f0882bc8d5d9798ef32b577a89bc
> # good: [e88fed94388f62a28acfef4954348abe79557d19] pid: sprinkle tasklist_lock asserts
> git bisect good e88fed94388f62a28acfef4954348abe79557d19
> # bad: [5ca27e0557d722dd648f949dde6e4997f6255f18] pid: drop irq disablement around pidmap_lock
> git bisect bad 5ca27e0557d722dd648f949dde6e4997f6255f18
> # bad: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock
> git bisect bad 88dec855ce117f52bcf88748ddcbb25b10f4f2fc
> # first bad commit: [88dec855ce117f52bcf88748ddcbb25b10f4f2fc] pid: perform free_pid() calls outside of tasklist_lock



-- 
Mateusz Guzik <mjguzik gmail.com>