linux.git/kernel/futex/waitwake.c, branch v6.18.21 Clone of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git futex: Correct the kernedoc return value for futex_wait_setup(). 2025-05-21T11:57:41+00:00 Sebastian Andrzej Siewior bigeasy@linutronix.de 2025-05-17T15:14:55+00:00 73c6c02b4febbb2c2761e559f31af8c7b87e81a5 The kerneldoc for futex_wait_setup() states it can return "0" or "<1". This isn't true because the error case is "<0" not less than 1. Document that <0 is returned on error. Drop the possible return values and state possible reasons. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: André Almeida <andrealmeid@igalia.com> Link: https://lore.kernel.org/r/20250517151455.1065363-6-bigeasy@linutronix.de 
The kerneldoc for futex_wait_setup() states it can return "0" or "<1".
This isn't true because the error case is "<0" not less than 1.

Document that <0 is returned on error. Drop the possible return values
and state possible reasons.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20250517151455.1065363-6-bigeasy@linutronix.de
futex: Fix kernel-doc comments 2025-05-16T07:33:53+00:00 Borislav Petkov (AMD) bp@alien8.de 2025-05-15T17:16:41+00:00 bd59f6170968314c82e2b65f8bbaec55896b7a5f Fix those: ./kernel/futex/futex.h:208: warning: Function parameter or struct member 'drop_hb_ref' not described in 'futex_q' ./kernel/futex/waitwake.c:343: warning: expecting prototype for futex_wait_queue(). Prototype was for futex_do_wait() instead ./kernel/futex/waitwake.c:594: warning: Function parameter or struct member 'task' not described in 'futex_wait_setup' Fixes: 93f1b6d79a73 ("futex: Move futex_queue() into futex_wait_setup()") Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/20250512185641.0450a99b@canb.auug.org.au # report Link: https://lore.kernel.org/r/20250515171641.24073-1-bp@kernel.org # submission 
Fix those:

  ./kernel/futex/futex.h:208: warning: Function parameter or struct member 'drop_hb_ref' not described in 'futex_q'
  ./kernel/futex/waitwake.c:343: warning: expecting prototype for futex_wait_queue(). Prototype was for futex_do_wait() instead
  ./kernel/futex/waitwake.c:594: warning: Function parameter or struct member 'task' not described in 'futex_wait_setup'

Fixes: 93f1b6d79a73 ("futex: Move futex_queue() into futex_wait_setup()")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250512185641.0450a99b@canb.auug.org.au # report
Link: https://lore.kernel.org/r/20250515171641.24073-1-bp@kernel.org     # submission
futex: Acquire a hash reference in futex_wait_multiple_setup() 2025-05-03T10:02:06+00:00 Sebastian Andrzej Siewior bigeasy@linutronix.de 2025-04-16T16:29:08+00:00 3f6b233018af2a6fb449faa324d94a437e2e47ce futex_wait_multiple_setup() changes task_struct::__state to !TASK_RUNNING and then enqueues on multiple futexes. Every futex_q_lock() acquires a reference on the global hash which is dropped later. If a rehash is in progress then the loop will block on mm_struct::futex_hash_bucket for the rehash to complete and this will lose the previously set task_struct::__state. Acquire a reference on the local hash to avoiding blocking on mm_struct::futex_hash_bucket. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250416162921.513656-9-bigeasy@linutronix.de 
futex_wait_multiple_setup() changes task_struct::__state to
!TASK_RUNNING and then enqueues on multiple futexes. Every
futex_q_lock() acquires a reference on the global hash which is
dropped later.

If a rehash is in progress then the loop will block on
mm_struct::futex_hash_bucket for the rehash to complete and this will
lose the previously set task_struct::__state.

Acquire a reference on the local hash to avoiding blocking on
mm_struct::futex_hash_bucket.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-9-bigeasy@linutronix.de
futex: Create futex_hash() get/put class 2025-05-03T10:02:06+00:00 Peter Zijlstra peterz@infradead.org 2025-04-16T16:29:06+00:00 6c67f8d880c0950215b8e6f8539562ad1971a05a This gets us: hb = futex_hash(key) /* gets hb and inc users */ futex_hash_get(hb) /* inc users */ futex_hash_put(hb) /* dec users */ Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250416162921.513656-7-bigeasy@linutronix.de 
This gets us:

  hb = futex_hash(key) /* gets hb and inc users */
  futex_hash_get(hb)   /* inc users */
  futex_hash_put(hb)   /* dec users */

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-7-bigeasy@linutronix.de
futex: Create hb scopes 2025-05-03T10:02:05+00:00 Peter Zijlstra peterz@infradead.org 2025-04-16T16:29:05+00:00 8486d12f558ff9e4e90331e8ef841d84bf3a8c24 Create explicit scopes for hb variables; almost pure re-indent. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250416162921.513656-6-bigeasy@linutronix.de 
Create explicit scopes for hb variables; almost pure re-indent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-6-bigeasy@linutronix.de
futex: Pull futex_hash() out of futex_q_lock() 2025-05-03T10:02:05+00:00 Peter Zijlstra peterz@infradead.org 2025-04-16T16:29:04+00:00 2fb292096d950a67a1941949a08a60ddd3193da3 Getting the hash bucket and queuing it are two distinct actions. In light of wanting to add a put hash bucket function later, untangle them. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250416162921.513656-5-bigeasy@linutronix.de 
Getting the hash bucket and queuing it are two distinct actions. In
light of wanting to add a put hash bucket function later, untangle
them.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-5-bigeasy@linutronix.de
futex: Move futex_queue() into futex_wait_setup() 2025-05-03T10:02:05+00:00 Peter Zijlstra peterz@infradead.org 2025-04-16T16:29:03+00:00 93f1b6d79a73b520b6875cf3babf4a09acc4eef0 futex_wait_setup() has a weird calling convention in order to return hb to use as an argument to futex_queue(). Mostly such that requeue can have an extra test in between. Reorder code a little to get rid of this and keep the hb usage inside futex_wait_setup(). [bigeasy: fixes] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250416162921.513656-4-bigeasy@linutronix.de 
futex_wait_setup() has a weird calling convention in order to return
hb to use as an argument to futex_queue().

Mostly such that requeue can have an extra test in between.

Reorder code a little to get rid of this and keep the hb usage inside
futex_wait_setup().

[bigeasy: fixes]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-4-bigeasy@linutronix.de
Merge tag 'locking-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2025-02-08T18:54:11+00:00 Linus Torvalds torvalds@linux-foundation.org 2025-02-08T18:54:11+00:00 fa76887bb72ae11347730271e6a04c147b7527e6 Pull locking fix from Ingo Molnar: "Fix a dangling pointer bug in the futex code used by the uring code. It isn't causing problems at the moment due to uring ABI limitations leaving it essentially unused in current usages, but is a good idea to fix nevertheless" * tag 'locking-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: futex: Pass in task to futex_queue() 
Pull locking fix from Ingo Molnar:
 "Fix a dangling pointer bug in the futex code used by the uring code.

  It isn't causing problems at the moment due to uring ABI limitations
  leaving it essentially unused in current usages, but is a good idea to
  fix nevertheless"

* tag 'locking-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Pass in task to futex_queue()
futex: Pass in task to futex_queue() 2025-01-24T08:37:30+00:00 Jens Axboe axboe@kernel.dk 2025-01-15T16:05:15+00:00 5e0e02f0d7e52cfc8b1adfc778dd02181d8b47b4 futex_queue() -> __futex_queue() uses 'current' as the task to store in the struct futex_q->task field. This is fine for synchronous usage of the futex infrastructure, but it's not always correct when used by io_uring where the task doing the initial futex_queue() might not be available later on. This doesn't lead to any issues currently, as the io_uring side doesn't support PI futexes, but it does leave a potentially dangling pointer which is never a good idea. Have futex_queue() take a task_struct argument, and have the regular callers pass in 'current' for that. Meanwhile io_uring can just pass in NULL, as the task should never be used off that path. In theory req->tctx->task could be used here, but there's no point populating it with a task field that will never be used anyway. Reported-by: Jann Horn <jannh@google.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/all/22484a23-542c-4003-b721-400688a0d055@kernel.dk 
futex_queue() -> __futex_queue() uses 'current' as the task to store in
the struct futex_q->task field. This is fine for synchronous usage of
the futex infrastructure, but it's not always correct when used by
io_uring where the task doing the initial futex_queue() might not be
available later on. This doesn't lead to any issues currently, as the
io_uring side doesn't support PI futexes, but it does leave a
potentially dangling pointer which is never a good idea.

Have futex_queue() take a task_struct argument, and have the regular
callers pass in 'current' for that. Meanwhile io_uring can just pass in
NULL, as the task should never be used off that path. In theory
req->tctx->task could be used here, but there's no point populating it
with a task field that will never be used anyway.

Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/22484a23-542c-4003-b721-400688a0d055@kernel.dk
kernel: remove get_task_comm() and print task comm directly 2025-01-13T04:21:15+00:00 Yafang Shao laoar.shao@gmail.com 2024-12-19T02:34:48+00:00 b6dcdb06c064b520a3f406bfdc4d64510cf84108 Patch series "Remove get_task_comm() and print task comm directly", v2. Since task->comm is guaranteed to be NUL-terminated, we can print it directly without the need to copy it into a separate buffer. This simplifies the code and avoids unnecessary operations. This patch (of 5): Since task->comm is guaranteed to be NUL-terminated, we can print it directly without the need to copy it into a separate buffer. This simplifies the code and avoids unnecessary operations. Link: https://lkml.kernel.org/r/20241219023452.69907-1-laoar.shao@gmail.com Link: https://lkml.kernel.org/r/20241219023452.69907-2-laoar.shao@gmail.com Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Cc: Serge Hallyn <serge@hallyn.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Darren Hart <dvhart@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: "André Almeida" <andrealmeid@igalia.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Borislav Petkov (AMD) <bp@alien8.de> Cc: Kalle Valo <kvalo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Petr Mladek <pmladek@suse.com> Cc: Danilo Krummrich <dakr@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Airlie <airlied@gmail.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: James Morris <jmorris@namei.org> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: Jiri Slaby <jirislaby@kernel.org> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Karol Herbst <kherbst@redhat.com> Cc: Kees Cook <kees@kernel.org> Cc: Lyude Paul <lyude@redhat.com> Cc: Oded Gabbay <ogabbay@kernel.org> Cc: Paul Moore <paul@paul-moore.com> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Simona Vetter <simona@ffwll.ch> Cc: Tvrtko Ursulin <tursulin@ursulin.net> Cc: Vineet Gupta <vgupta@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> 
Patch series "Remove get_task_comm() and print task comm directly", v2.

Since task->comm is guaranteed to be NUL-terminated, we can print it
directly without the need to copy it into a separate buffer.  This
simplifies the code and avoids unnecessary operations.


This patch (of 5):

Since task->comm is guaranteed to be NUL-terminated, we can print it
directly without the need to copy it into a separate buffer.  This
simplifies the code and avoids unnecessary operations.

Link: https://lkml.kernel.org/r/20241219023452.69907-1-laoar.shao@gmail.com
Link: https://lkml.kernel.org/r/20241219023452.69907-2-laoar.shao@gmail.com
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "André Almeida" <andrealmeid@igalia.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Kalle Valo <kvalo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Oded Gabbay <ogabbay@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: Vineet Gupta <vgupta@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>