[PATCH] mm: Remove pointless might_sleep() in remove_vm_area().

Andrey Ryabinin wrote:

It's safe to call vfree() from rcu callback as in any other interrupt context.
Commits you listed bellow didn't change anything in that respect.
They made impossible to call vfree() under stuff like preempt_disable()/spin_lock()

I still cannot catch. According to test results shown below, calling vfree() from
RCU callback is permitted but calling vfree() from RCU read section is no longer
permitted.

---------- test.c ----------
#include <linux/module.h>
static int test_init(void)
{
        rcu_read_lock();
        might_sleep();
        rcu_read_unlock();
        return -EINVAL;
}
module_init(test_init);
MODULE_LICENSE("GPL");
---------- test.c ----------

[   49.729561] test: loading out-of-tree module taints kernel.
[   49.738211] test: module verification failed: signature and/or required key missing - tainting kernel

[   49.757855] ===============================
[   49.764038] [ ERR: suspicious RCU usage.  ]
[   49.767222] 4.11.0-rc4+ #210 Tainted: G           OE
[   49.770216] -------------------------------
[   49.772668] ./include/linux/rcupdate.h:521 Illegal context switch in RCU read-side critical section!
[   49.777915]
other info that might help us debug this:

[   49.782562]
rcu_scheduler_active = 2, debug_locks = 0
[   49.786336] 1 lock held by insmod/2332:
[   49.788596]  #0:  (rcu_read_lock){......}, at: [<ffffffffc07c7005>] test_init+0x5/0x1000 [test]
[   49.793632]
stack backtrace:
[   49.796190] CPU: 2 PID: 2332 Comm: insmod Tainted: G           OE   4.11.0-rc4+ #210
[   49.798830] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[   49.802213] Call Trace:
[   49.803010]  dump_stack+0x85/0xc9
[   49.804079]  lockdep_rcu_suspicious+0xe7/0x120
[   49.805503]  ___might_sleep+0xac/0x250
[   49.806704]  __might_sleep+0x4a/0x90
[   49.807852]  ? 0xffffffffc07c7000
[   49.808921]  test_init+0x5c/0x1000 [test]
[   49.810212]  ? test_init+0x5/0x1000 [test]
[   49.811526]  do_one_initcall+0x51/0x1c0
[   49.813014]  ? do_init_module+0x27/0x1fc
[   49.814370]  ? rcu_read_lock_sched_held+0x98/0xa0
[   49.815882]  ? kmem_cache_alloc_trace+0x278/0x2e0
[   49.817389]  ? do_init_module+0x27/0x1fc
[   49.818651]  do_init_module+0x60/0x1fc
[   49.819880]  load_module+0x23b4/0x2a00
[   49.821087]  ? __symbol_put+0x70/0x70
[   49.822271]  ? vfs_read+0x12b/0x180
[   49.823401]  SYSC_finit_module+0xa6/0xf0
[   49.824667]  SyS_finit_module+0xe/0x10
[   49.825894]  do_syscall_64+0x6c/0x200
[   49.827074]  entry_SYSCALL64_slow_path+0x25/0x25
[   49.829239] RIP: 0033:0x7fdeb1f52bf9
[   49.830540] RSP: 002b:00007fff1f355b28 EFLAGS: 00000206 ORIG_RAX: 0000000000000139
[   49.833255] RAX: ffffffffffffffda RBX: 00000000014e71f0 RCX: 00007fdeb1f52bf9
[   49.835586] RDX: 0000000000000000 RSI: 000000000041a2d8 RDI: 0000000000000003
[   49.838370] RBP: 000000000041a2d8 R08: 0000000000000000 R09: 00007fff1f355cc8
[   49.841099] R10: 0000000000000003 R11: 0000000000000206 R12: 0000000000000000
[   49.843994] R13: 00000000014e6130 R14: 0000000000000000 R15: 0000000000000000
[   49.846756] BUG: sleeping function called from invalid context at /data/linux/akari/test.c:5
[   49.850727] in_atomic(): 1, irqs_disabled(): 0, pid: 2332, name: insmod
[   49.853353] INFO: lockdep is turned off.
[   49.855088] CPU: 2 PID: 2332 Comm: insmod Tainted: G           OE   4.11.0-rc4+ #210
[   49.858013] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[   49.861940] Call Trace:
[   49.863217]  dump_stack+0x85/0xc9
[   49.864744]  ___might_sleep+0x184/0x250
[   49.866420]  __might_sleep+0x4a/0x90
[   49.868003]  ? 0xffffffffc07c7000
[   49.869502]  test_init+0x5c/0x1000 [test]
[   49.871236]  ? test_init+0x5/0x1000 [test]
[   49.872983]  do_one_initcall+0x51/0x1c0
[   49.874796]  ? do_init_module+0x27/0x1fc
[   49.876486]  ? rcu_read_lock_sched_held+0x98/0xa0
[   49.878413]  ? kmem_cache_alloc_trace+0x278/0x2e0
[   49.880330]  ? do_init_module+0x27/0x1fc
[   49.882006]  do_init_module+0x60/0x1fc
[   49.883623]  load_module+0x23b4/0x2a00
[   49.885225]  ? __symbol_put+0x70/0x70
[   49.886784]  ? vfs_read+0x12b/0x180
[   49.888291]  SYSC_finit_module+0xa6/0xf0
[   49.890025]  SyS_finit_module+0xe/0x10
[   49.891611]  do_syscall_64+0x6c/0x200
[   49.893168]  entry_SYSCALL64_slow_path+0x25/0x25
[   49.895027] RIP: 0033:0x7fdeb1f52bf9
[   49.896561] RSP: 002b:00007fff1f355b28 EFLAGS: 00000206 ORIG_RAX: 0000000000000139
[   49.899355] RAX: ffffffffffffffda RBX: 00000000014e71f0 RCX: 00007fdeb1f52bf9
[   49.902020] RDX: 0000000000000000 RSI: 000000000041a2d8 RDI: 0000000000000003
[   49.904683] RBP: 000000000041a2d8 R08: 0000000000000000 R09: 00007fff1f355cc8
[   49.907510] R10: 0000000000000003 R11: 0000000000000206 R12: 0000000000000000
[   49.910180] R13: 00000000014e6130 R14: 0000000000000000 R15: 0000000000000000

---------- test.c ----------
#include <linux/module.h>
#include <linux/sched.h>
static int test_init(void)
{
        static DEFINE_SPINLOCK(lock);
        rcu_read_lock();
        spin_lock(&lock);
        cond_resched_lock(&lock);
        spin_unlock(&lock);
        rcu_read_unlock();
        return -EINVAL;
}
module_init(test_init);
MODULE_LICENSE("GPL");
---------- test.c ----------

[   66.548461] test: loading out-of-tree module taints kernel.
[   66.551894] test: module verification failed: signature and/or required key missing - tainting kernel

[   66.560299] ===============================
[   66.562838] [ ERR: suspicious RCU usage.  ]
[   66.565395] 4.11.0-rc4+ #210 Tainted: G           OE
[   66.568494] -------------------------------
[   66.571012] ./include/linux/rcupdate.h:521 Illegal context switch in RCU read-side critical section!
[   66.576384]
other info that might help us debug this:

[   66.579234]
rcu_scheduler_active = 2, debug_locks = 0
[   66.581505] 2 locks held by insmod/2336:
[   66.582897]  #0:  (rcu_read_lock){......}, at: [<ffffffffc0543005>] test_init+0x5/0x1000 [test]
[   66.586253]  #1:  (lock#4){+.+...}, at: [<ffffffffc0543055>] test_init+0x55/0x1000 [test]
[   66.589135]
stack backtrace:
[   66.590919] CPU: 0 PID: 2336 Comm: insmod Tainted: G           OE   4.11.0-rc4+ #210
[   66.593842] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[   66.597716] Call Trace:
[   66.598598]  dump_stack+0x85/0xc9
[   66.599749]  lockdep_rcu_suspicious+0xe7/0x120
[   66.601289]  ___might_sleep+0xac/0x250
[   66.602585]  ? 0xffffffffc0543000
[   66.603735]  test_init+0x6b/0x1000 [test]
[   66.605121]  ? test_init+0x5/0x1000 [test]
[   66.606520]  do_one_initcall+0x51/0x1c0
[   66.607850]  ? do_init_module+0x27/0x1fc
[   66.609245]  ? rcu_read_lock_sched_held+0x98/0xa0
[   66.610855]  ? kmem_cache_alloc_trace+0x278/0x2e0
[   66.612489]  ? do_init_module+0x27/0x1fc
[   66.613868]  do_init_module+0x60/0x1fc
[   66.615195]  load_module+0x23b4/0x2a00
[   66.616512]  ? __symbol_put+0x70/0x70
[   66.617816]  ? vfs_read+0x12b/0x180
[   66.619074]  SYSC_finit_module+0xa6/0xf0
[   66.620455]  SyS_finit_module+0xe/0x10
[   66.621780]  do_syscall_64+0x6c/0x200
[   66.623067]  entry_SYSCALL64_slow_path+0x25/0x25
[   66.624937] RIP: 0033:0x7f6e6702bbf9
[   66.626206] RSP: 002b:00007ffdc94c3588 EFLAGS: 00000206 ORIG_RAX: 0000000000000139
[   66.628901] RAX: ffffffffffffffda RBX: 00000000007421f0 RCX: 00007f6e6702bbf9
[   66.631373] RDX: 0000000000000000 RSI: 000000000041a2d8 RDI: 0000000000000003
[   66.634430] RBP: 000000000041a2d8 R08: 0000000000000000 R09: 00007ffdc94c3728
[   66.637428] R10: 0000000000000003 R11: 0000000000000206 R12: 0000000000000000
[   66.640422] R13: 0000000000741130 R14: 0000000000000000 R15: 0000000000000000
[   66.643430] BUG: sleeping function called from invalid context at /data/linux/akari/test.c:8
[   66.646779] in_atomic(): 1, irqs_disabled(): 0, pid: 2336, name: insmod
[   66.649484] INFO: lockdep is turned off.
[   66.651284] CPU: 0 PID: 2336 Comm: insmod Tainted: G           OE   4.11.0-rc4+ #210
[   66.654377] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[   66.658592] Call Trace:
[   66.659939]  dump_stack+0x85/0xc9
[   66.661562]  ___might_sleep+0x184/0x250
[   66.663385]  ? 0xffffffffc0543000
[   66.664967]  test_init+0x6b/0x1000 [test]
[   66.666812]  ? test_init+0x5/0x1000 [test]
[   66.668636]  do_one_initcall+0x51/0x1c0
[   66.670399]  ? do_init_module+0x27/0x1fc
[   66.672170]  ? rcu_read_lock_sched_held+0x98/0xa0
[   66.674256]  ? kmem_cache_alloc_trace+0x278/0x2e0
[   66.676308]  ? do_init_module+0x27/0x1fc
[   66.678056]  do_init_module+0x60/0x1fc
[   66.679728]  load_module+0x23b4/0x2a00
[   66.681428]  ? __symbol_put+0x70/0x70
[   66.683100]  ? vfs_read+0x12b/0x180
[   66.684720]  SYSC_finit_module+0xa6/0xf0
[   66.686422]  SyS_finit_module+0xe/0x10
[   66.688109]  do_syscall_64+0x6c/0x200
[   66.689776]  entry_SYSCALL64_slow_path+0x25/0x25
[   66.692052] RIP: 0033:0x7f6e6702bbf9
[   66.693687] RSP: 002b:00007ffdc94c3588 EFLAGS: 00000206 ORIG_RAX: 0000000000000139
[   66.696577] RAX: ffffffffffffffda RBX: 00000000007421f0 RCX: 00007f6e6702bbf9
[   66.699432] RDX: 0000000000000000 RSI: 000000000041a2d8 RDI: 0000000000000003
[   66.702261] RBP: 000000000041a2d8 R08: 0000000000000000 R09: 00007ffdc94c3728
[   66.705076] R10: 0000000000000003 R11: 0000000000000206 R12: 0000000000000000
[   66.707990] R13: 0000000000741130 R14: 0000000000000000 R15: 0000000000000000



Also, if we try below change like suggested at
http://lkml.kernel.org/r/20170323152949.GA29134 at bombadil.infradead.org ,
we get below warnings.
Aren't there vfree()/kvfree() users who are not ready to handle these changes?

----------

diff --git a/mm/util.c b/mm/util.c
index 656dc5e..2a2ef72 100644
--- a/mm/util.c
+++ b/mm/util.c

@@ -331,6 +331,12 @@ unsigned long vm_mmap(struct file *file, unsigned long addr,
 
 void kvfree(const void *addr)
 {
+	/* Detect errors before kvmalloc() falls back to vmalloc(). */
+	if (addr) {
+		WARN_ON(in_nmi());
+		if (likely(!in_interrupt()))
+			might_sleep();
+	}
 	if (is_vmalloc_addr(addr))
 		vfree(addr);
 	else
----------

[   23.635540] BUG: sleeping function called from invalid context at mm/util.c:338
[   23.638701] in_atomic(): 1, irqs_disabled(): 0, pid: 478, name: kworker/0:1H
[   23.641516] 3 locks held by kworker/0:1H/478:
[   23.643476]  #0:  ("xfs-log/%s"mp->m_fsname){.+.+..}, at: [<ffffffffb20d1e64>] process_one_work+0x194/0x6c0
[   23.647176]  #1:  ((&bp->b_ioend_work)){+.+...}, at: [<ffffffffb20d1e64>] process_one_work+0x194/0x6c0
[   23.650939]  #2:  (&(&pag->pagb_lock)->rlock){+.+...}, at: [<ffffffffc02b42ee>] xfs_extent_busy_clear+0x9e/0xe0 [xfs]
[   23.655132] CPU: 0 PID: 478 Comm: kworker/0:1H Not tainted 4.11.0-rc4+ #212
[   23.657974] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[   23.662041] Workqueue: xfs-log/sda1 xfs_buf_ioend_work [xfs]
[   23.664463] Call Trace:
[   23.665866]  dump_stack+0x85/0xc9
[   23.667538]  ___might_sleep+0x184/0x250
[   23.669371]  __might_sleep+0x4a/0x90
[   23.671137]  kvfree+0x41/0x90
[   23.672748]  xfs_extent_busy_clear_one+0x51/0x190 [xfs]
[   23.675110]  xfs_extent_busy_clear+0xbb/0xe0 [xfs]
[   23.677278]  xlog_cil_committed+0x241/0x420 [xfs]
[   23.679431]  xlog_state_do_callback+0x170/0x2d0 [xfs]
[   23.681717]  xlog_state_done_syncing+0x7f/0xa0 [xfs]
[   23.683971]  ? xfs_buf_ioend_work+0x15/0x20 [xfs]
[   23.686112]  xlog_iodone+0x86/0xc0 [xfs]
[   23.688007]  xfs_buf_ioend+0xd3/0x440 [xfs]
[   23.689999]  xfs_buf_ioend_work+0x15/0x20 [xfs]
[   23.692060]  process_one_work+0x21c/0x6c0
[   23.694177]  ? process_one_work+0x194/0x6c0
[   23.696120]  worker_thread+0x137/0x4b0
[   23.697973]  kthread+0x10f/0x150
[   23.699607]  ? process_one_work+0x6c0/0x6c0
[   23.701561]  ? kthread_create_on_node+0x70/0x70
[   23.703617]  ret_from_fork+0x31/0x40
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