The patch titled
Subject: mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct
has been added to the -mm tree. Its filename is
mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct.patch
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------------------------------------------------------
From: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Subject: mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct
mmap_sem is on the hot path of kernel, and it very contended, but it is
abused too. It is used to protect arg_start|end and evn_start|end when
reading /proc/$PID/cmdline and /proc/$PID/environ, but it doesn't make
sense since those proc files just expect to read 4 values atomically and
not related to VM, they could be set to arbitrary values by C/R.
And, the mmap_sem contention may cause unexpected issue like below:
INFO: task ps:14018 blocked for more than 120 seconds.
Tainted: G E 4.9.79-009.ali3000.alios7.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
ps D 0 14018 1 0x00000004
ffff885582f84000 ffff885e8682f000 ffff880972943000 ffff885ebf499bc0
ffff8828ee120000 ffffc900349bfca8 ffffffff817154d0 0000000000000040
00ffffff812f872a ffff885ebf499bc0 024000d000948300 ffff880972943000
Call Trace:
[<ffffffff817154d0>] ? __schedule+0x250/0x730
[<ffffffff817159e6>] schedule+0x36/0x80
[<ffffffff81718560>] rwsem_down_read_failed+0xf0/0x150
[<ffffffff81390a28>] call_rwsem_down_read_failed+0x18/0x30
[<ffffffff81717db0>] down_read+0x20/0x40
[<ffffffff812b9439>] proc_pid_cmdline_read+0xd9/0x4e0
[<ffffffff81253c95>] ? do_filp_open+0xa5/0x100
[<ffffffff81241d87>] __vfs_read+0x37/0x150
[<ffffffff812f824b>] ? security_file_permission+0x9b/0xc0
[<ffffffff81242266>] vfs_read+0x96/0x130
[<ffffffff812437b5>] SyS_read+0x55/0xc0
[<ffffffff8171a6da>] entry_SYSCALL_64_fastpath+0x1a/0xc5
Both Alexey Dobriyan and Michal Hocko suggested to use dedicated lock for
them to mitigate the abuse of mmap_sem.
So, introduce a new spinlock in mm_struct to protect the concurrent access
to arg_start|end, env_start|end and others, as well as replace write
map_sem to read to protect the race condition between prctl and sys_brk
which might break check_data_rlimit(), and makes prctl more friendly to
other VM operations.
This patch just eliminates the abuse of mmap_sem, but it can't resolve the
above hung task warning completely since the later access_remote_vm() call
needs acquire mmap_sem. The mmap_sem scalability issue will be solved in
the future.
Link: http://lkml.kernel.org/r/1523730291-109696-1-git-send-email-yang.shi@xxxxxxxxxxxxxxxxx
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mateusz Guzik <mguzik@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 8 ++++----
include/linux/mm_types.h | 2 ++
kernel/fork.c | 1 +
kernel/sys.c | 6 ++++--
mm/init-mm.c | 1 +
5 files changed, 12 insertions(+), 6 deletions(-)
diff -puN fs/proc/base.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct fs/proc/base.c
--- a/fs/proc/base.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct
+++ a/fs/proc/base.c
@@ -239,12 +239,12 @@ static ssize_t proc_pid_cmdline_read(str
goto out_mmput;
}
- down_read(&mm->mmap_sem);
+ spin_lock(&mm->arg_lock);
arg_start = mm->arg_start;
arg_end = mm->arg_end;
env_start = mm->env_start;
env_end = mm->env_end;
- up_read(&mm->mmap_sem);
+ spin_unlock(&mm->arg_lock);
BUG_ON(arg_start > arg_end);
BUG_ON(env_start > env_end);
@@ -929,10 +929,10 @@ static ssize_t environ_read(struct file
if (!mmget_not_zero(mm))
goto free;
- down_read(&mm->mmap_sem);
+ spin_lock(&mm->arg_lock);
env_start = mm->env_start;
env_end = mm->env_end;
- up_read(&mm->mmap_sem);
+ spin_unlock(&mm->arg_lock);
while (count > 0) {
size_t this_len, max_len;
diff -puN include/linux/mm_types.h~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct
+++ a/include/linux/mm_types.h
@@ -413,6 +413,8 @@ struct mm_struct {
unsigned long exec_vm; /* VM_EXEC & ~VM_WRITE & ~VM_STACK */
unsigned long stack_vm; /* VM_STACK */
unsigned long def_flags;
+
+ spinlock_t arg_lock; /* protect the below fields */
unsigned long start_code, end_code, start_data, end_data;
unsigned long start_brk, brk, start_stack;
unsigned long arg_start, arg_end, env_start, env_end;
diff -puN kernel/fork.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct kernel/fork.c
--- a/kernel/fork.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct
+++ a/kernel/fork.c
@@ -900,6 +900,7 @@ static struct mm_struct *mm_init(struct
mm->pinned_vm = 0;
memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
spin_lock_init(&mm->page_table_lock);
+ spin_lock_init(&mm->arg_lock);
mm_init_cpumask(mm);
mm_init_aio(mm);
mm_init_owner(mm, p);
diff -puN kernel/sys.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct kernel/sys.c
--- a/kernel/sys.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct
+++ a/kernel/sys.c
@@ -2011,7 +2011,7 @@ static int prctl_set_mm_map(int opt, con
return error;
}
- down_write(&mm->mmap_sem);
+ down_read(&mm->mmap_sem);
/*
* We don't validate if these members are pointing to
@@ -2025,6 +2025,7 @@ static int prctl_set_mm_map(int opt, con
* to any problem in kernel itself
*/
+ spin_lock(&mm->arg_lock);
mm->start_code = prctl_map.start_code;
mm->end_code = prctl_map.end_code;
mm->start_data = prctl_map.start_data;
@@ -2036,6 +2037,7 @@ static int prctl_set_mm_map(int opt, con
mm->arg_end = prctl_map.arg_end;
mm->env_start = prctl_map.env_start;
mm->env_end = prctl_map.env_end;
+ spin_unlock(&mm->arg_lock);
/*
* Note this update of @saved_auxv is lockless thus
@@ -2048,7 +2050,7 @@ static int prctl_set_mm_map(int opt, con
if (prctl_map.auxv_size)
memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv));
- up_write(&mm->mmap_sem);
+ up_read(&mm->mmap_sem);
return 0;
}
#endif /* CONFIG_CHECKPOINT_RESTORE */
diff -puN mm/init-mm.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct mm/init-mm.c
--- a/mm/init-mm.c~mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct
+++ a/mm/init-mm.c
@@ -22,6 +22,7 @@ struct mm_struct init_mm = {
.mm_count = ATOMIC_INIT(1),
.mmap_sem = __RWSEM_INITIALIZER(init_mm.mmap_sem),
.page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
+ .arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
.user_ns = &init_user_ns,
INIT_MM_CONTEXT(init_mm)
_
Patches currently in -mm which might be from yang.shi@xxxxxxxxxxxxxxxxx are
mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct.patch
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