Commit b18cb64e authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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fs/proc: Stop trying to report thread stacks 

This reverts more of:

  b7643757 ("procfs: mark thread stack correctly in proc/<pid>/maps")

... which was partially reverted by:

  65376df5 ("proc: revert /proc/<pid>/maps [stack:TID] annotation")

Originally, /proc/PID/task/TID/maps was the same as /proc/TID/maps.

In current kernels, /proc/PID/maps (or /proc/TID/maps even for
threads) shows "[stack]" for VMAs in the mm's stack address range.

In contrast, /proc/PID/task/TID/maps uses KSTK_ESP to guess the
target thread's stack's VMA.  This is racy, probably returns garbage
and, on arches with CONFIG_TASK_INFO_IN_THREAD=y, is also crash-prone:
KSTK_ESP is not safe to use on tasks that aren't known to be running
ordinary process-context kernel code.

This patch removes the difference and just shows "[stack]" for VMAs
in the mm's stack range.  This is IMO much more sensible -- the
actual "stack" address really is treated specially by the VM code,
and the current thread stack isn't even well-defined fo...
parent 0a1eb2d4

Documentation/filesystems/proc.txt

+0 −26
Original line number Diff line number Diff line
@@ -395,32 +395,6 @@ is not associated with a file: 


 or if empty, the mapping is anonymous.



The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint

of the individual tasks of a process. In this file you will see a mapping marked

as [stack] if that task sees it as a stack. Hence, for the example above, the

task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:



08048000-08049000 r-xp 00000000 03:00 8312       /opt/test

08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test

0804a000-0806b000 rw-p 00000000 00:00 0          [heap]

a7cb1000-a7cb2000 ---p 00000000 00:00 0

a7cb2000-a7eb2000 rw-p 00000000 00:00 0

a7eb2000-a7eb3000 ---p 00000000 00:00 0

a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]

a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6

a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6

a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6

a800b000-a800e000 rw-p 00000000 00:00 0

a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0

a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0

a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0

a8024000-a8027000 rw-p 00000000 00:00 0

a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2

a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2

a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2

aff35000-aff4a000 rw-p 00000000 00:00 0

ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]



The /proc/PID/smaps is an extension based on maps, showing the memory

consumption for each of the process's mappings. For each of mappings there

is a series of lines such as the following:

fs/proc/task_mmu.c

+10 −19
Original line number Diff line number Diff line
@@ -266,24 +266,15 @@ static int do_maps_open(struct inode *inode, struct file *file, 
 * /proc/PID/maps that is the stack of the main task.

 */

static int is_stack(struct proc_maps_private *priv,

		    struct vm_area_struct *vma, int is_pid)

		    struct vm_area_struct *vma)

{

	int stack = 0;



	if (is_pid) {

		stack = vma->vm_start <= vma->vm_mm->start_stack &&

	/*

	 * We make no effort to guess what a given thread considers to be

	 * its "stack".  It's not even well-defined for programs written

	 * languages like Go.

	 */

	return vma->vm_start <= vma->vm_mm->start_stack &&

		vma->vm_end >= vma->vm_mm->start_stack;

	} else {

		struct inode *inode = priv->inode;

		struct task_struct *task;



		rcu_read_lock();

		task = pid_task(proc_pid(inode), PIDTYPE_PID);

		if (task)

			stack = vma_is_stack_for_task(vma, task);

		rcu_read_unlock();

	}

	return stack;

}



static void
@@ -354,7 +345,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid) 
			goto done;

		}



		if (is_stack(priv, vma, is_pid))

		if (is_stack(priv, vma))

			name = "[stack]";

	}
@@ -1669,7 +1660,7 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid) 
		seq_file_path(m, file, "\n\t= ");

	} else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) {

		seq_puts(m, " heap");

	} else if (is_stack(proc_priv, vma, is_pid)) {

	} else if (is_stack(proc_priv, vma)) {

		seq_puts(m, " stack");

	}

fs/proc/task_nommu.c

+10 −18
Original line number Diff line number Diff line
@@ -124,25 +124,17 @@ unsigned long task_statm(struct mm_struct *mm, 
}



static int is_stack(struct proc_maps_private *priv,

		    struct vm_area_struct *vma, int is_pid)

		    struct vm_area_struct *vma)

{

	struct mm_struct *mm = vma->vm_mm;

	int stack = 0;



	if (is_pid) {

		stack = vma->vm_start <= mm->start_stack &&

	/*

	 * We make no effort to guess what a given thread considers to be

	 * its "stack".  It's not even well-defined for programs written

	 * languages like Go.

	 */

	return vma->vm_start <= mm->start_stack &&

		vma->vm_end >= mm->start_stack;

	} else {

		struct inode *inode = priv->inode;

		struct task_struct *task;



		rcu_read_lock();

		task = pid_task(proc_pid(inode), PIDTYPE_PID);

		if (task)

			stack = vma_is_stack_for_task(vma, task);

		rcu_read_unlock();

	}

	return stack;

}



/*
@@ -184,7 +176,7 @@ static int nommu_vma_show(struct seq_file *m, struct vm_area_struct *vma, 
	if (file) {

		seq_pad(m, ' ');

		seq_file_path(m, file, "");

	} else if (mm && is_stack(priv, vma, is_pid)) {

	} else if (mm && is_stack(priv, vma)) {

		seq_pad(m, ' ');

		seq_printf(m, "[stack]");

	}