Re: [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()

[Yang Shi]

On 2/26/18 11:15 PM, Alexey Dobriyan wrote:

On Tue, Feb 27, 2018 at 08:25:50AM +0800, Yang Shi wrote:

Like reading /proc/*/cmdline, it is possible to be blocked for long time
when reading /proc/*/environ when manipulating large mapping at the mean
time. The environ reading process will be waiting for mmap_sem become
available for a long time then it may cause the reading task hung.

Convert down_read() and access_remote_vm() to killable version.

Signed-off-by: Yang Shi 
Suggested-by: Alexey Dobriyan 

Ehh, bloody tags.


I mean fix reading /proc/*/environ part.


I didn't suggest _killable() variants, they're quite ugly because API
multiplies. access_remote_vm() could be converted to down_read_killable().


There might be other places that need non-killable access_remote_vm(), 
like patch 4/4.


And, it sounds keeping access_remote_vm() semantic intact may prevent 
from confusion. The most people may get used to assume 
access_remote_vm() behaves like access_process_vm() except not inc mm 
reference count.


Thanks,
Yang




--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -933,7 +933,9 @@ static ssize_t environ_read(struct file *file, char __user 
*buf,
if (!mmget_not_zero(mm))
goto free;
  
-	down_read(&mm->mmap_sem);

+   ret = down_read_killable(&mm->mmap_sem);
+   if (ret)
+   goto out_mmput;
env_start = mm->env_start;
env_end = mm->env_end;
up_read(&mm->mmap_sem);
@@ -950,7 +952,8 @@ static ssize_t environ_read(struct file *file, char __user 
*buf,
max_len = min_t(size_t, PAGE_SIZE, count);
this_len = min(max_len, this_len);
  
-		retval = access_remote_vm(mm, (env_start + src), page, this_len, 0);

+   retval = access_remote_vm_killable(mm, (env_start + src),
+   page, this_len, 0);

Re: [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()

[Alexey Dobriyan]

On Tue, Feb 27, 2018 at 08:25:50AM +0800, Yang Shi wrote:
> Like reading /proc/*/cmdline, it is possible to be blocked for long time
> when reading /proc/*/environ when manipulating large mapping at the mean
> time. The environ reading process will be waiting for mmap_sem become
> available for a long time then it may cause the reading task hung.
> 
> Convert down_read() and access_remote_vm() to killable version.
> 
> Signed-off-by: Yang Shi 
> Suggested-by: Alexey Dobriyan 

Ehh, bloody tags.
I didn't suggest _killable() variants, they're quite ugly because API
multiplies. access_remote_vm() could be converted to down_read_killable().

> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -933,7 +933,9 @@ static ssize_t environ_read(struct file *file, char 
> __user *buf,
>   if (!mmget_not_zero(mm))
>   goto free;
>  
> - down_read(&mm->mmap_sem);
> + ret = down_read_killable(&mm->mmap_sem);
> + if (ret)
> + goto out_mmput;
>   env_start = mm->env_start;
>   env_end = mm->env_end;
>   up_read(&mm->mmap_sem);
> @@ -950,7 +952,8 @@ static ssize_t environ_read(struct file *file, char 
> __user *buf,
>   max_len = min_t(size_t, PAGE_SIZE, count);
>   this_len = min(max_len, this_len);
>  
> - retval = access_remote_vm(mm, (env_start + src), page, 
> this_len, 0);
> + retval = access_remote_vm_killable(mm, (env_start + src),
> + page, this_len, 0);

[PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()

[Yang Shi]

Like reading /proc/*/cmdline, it is possible to be blocked for long time
when reading /proc/*/environ when manipulating large mapping at the mean
time. The environ reading process will be waiting for mmap_sem become
available for a long time then it may cause the reading task hung.

Convert down_read() and access_remote_vm() to killable version.

Signed-off-by: Yang Shi 
Suggested-by: Alexey Dobriyan 
---
 fs/proc/base.c | 9 +++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9bdb84b..d87d9ab 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -933,7 +933,9 @@ static ssize_t environ_read(struct file *file, char __user 
*buf,
if (!mmget_not_zero(mm))
goto free;
 
-   down_read(&mm->mmap_sem);
+   ret = down_read_killable(&mm->mmap_sem);
+   if (ret)
+   goto out_mmput;
env_start = mm->env_start;
env_end = mm->env_end;
up_read(&mm->mmap_sem);
@@ -950,7 +952,8 @@ static ssize_t environ_read(struct file *file, char __user 
*buf,
max_len = min_t(size_t, PAGE_SIZE, count);
this_len = min(max_len, this_len);
 
-   retval = access_remote_vm(mm, (env_start + src), page, 
this_len, 0);
+   retval = access_remote_vm_killable(mm, (env_start + src),
+   page, this_len, 0);
 
if (retval <= 0) {
ret = retval;
@@ -968,6 +971,8 @@ static ssize_t environ_read(struct file *file, char __user 
*buf,
count -= retval;
}
*ppos = src;
+
+out_mmput:
mmput(mm);
 
 free:
-- 
1.8.3.1