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 <yang.shi@xxxxxxxxxxxxxxxxx>
Suggested-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
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);
--
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