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SubjectRe: Still a pretty bad time on 5.4.6 with fuse_request_end.
On Wed, Feb 12, 2020 at 10:38 AM Michael Stapelberg
<michael+lkml@stapelberg.ch> wrote:
>
> Unfortunately not: when I change the code like so:
>
> bool async;
> uint32_t opcode_early = req->args->opcode;
>
> if (test_and_set_bit(FR_FINISHED, &req->flags))
> goto put_request;
>
> async = req->args->end;
>
> …gdb only reports:
>
> (gdb) bt
> #0 0x000000a700000001 in ?? ()
> #1 0xffffffff8137fc99 in fuse_copy_finish (cs=0x20000ffffffff) at
> fs/fuse/dev.c:681
> Backtrace stopped: previous frame inner to this frame (corrupt stack?)
>
> But maybe that’s a hint in and of itself?

Yep, it's a stack use after return bug. Attached patch should fix
it, though I haven't tested it.

Thanks,
Miklos
---
fs/fuse/dev.c | 6 +++---
fs/fuse/fuse_i.h | 2 ++
2 files changed, 5 insertions(+), 3 deletions(-)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -276,12 +276,10 @@ static void flush_bg_queue(struct fuse_c
void fuse_request_end(struct fuse_conn *fc, struct fuse_req *req)
{
struct fuse_iqueue *fiq = &fc->iq;
- bool async;

if (test_and_set_bit(FR_FINISHED, &req->flags))
goto put_request;

- async = req->args->end;
/*
* test_and_set_bit() implies smp_mb() between bit
* changing and below intr_entry check. Pairs with
@@ -324,7 +322,7 @@ void fuse_request_end(struct fuse_conn *
wake_up(&req->waitq);
}

- if (async)
+ if (test_bit(FR_ASYNC, &req->flags))
req->args->end(fc, req->args, req->out.h.error);
put_request:
fuse_put_request(fc, req);
@@ -471,6 +469,8 @@ static void fuse_args_to_req(struct fuse
req->in.h.opcode = args->opcode;
req->in.h.nodeid = args->nodeid;
req->args = args;
+ if (args->end)
+ set_bit(FR_ASYNC, &req->flags);
}

ssize_t fuse_simple_request(struct fuse_conn *fc, struct fuse_args *args)
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -301,6 +301,7 @@ struct fuse_io_priv {
* FR_SENT: request is in userspace, waiting for an answer
* FR_FINISHED: request is finished
* FR_PRIVATE: request is on private list
+ * FR_ASYNC: request is asynchronous
*/
enum fuse_req_flag {
FR_ISREPLY,
@@ -314,6 +315,7 @@ enum fuse_req_flag {
FR_SENT,
FR_FINISHED,
FR_PRIVATE,
+ FR_ASYNC,
};

/**
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