This is a note to let you know that I've just added the patch titled
cifs: Release folio lock on fscache read hit.
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cifs-release-folio-lock-on-fscache-read-hit.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 69513dd669e243928f7450893190915a88f84a2b Mon Sep 17 00:00:00 2001
From: Russell Harmon via samba-technical <samba-technical@xxxxxxxxxxxxxxx>
Date: Thu, 10 Aug 2023 00:19:22 -0700
Subject: cifs: Release folio lock on fscache read hit.
From: Russell Harmon via samba-technical <samba-technical@xxxxxxxxxxxxxxx>
commit 69513dd669e243928f7450893190915a88f84a2b upstream.
Under the current code, when cifs_readpage_worker is called, the call
contract is that the callee should unlock the page. This is documented
in the read_folio section of Documentation/filesystems/vfs.rst as:
> The filesystem should unlock the folio once the read has completed,
> whether it was successful or not.
Without this change, when fscache is in use and cache hit occurs during
a read, the page lock is leaked, producing the following stack on
subsequent reads (via mmap) to the page:
$ cat /proc/3890/task/12864/stack
[<0>] folio_wait_bit_common+0x124/0x350
[<0>] filemap_read_folio+0xad/0xf0
[<0>] filemap_fault+0x8b1/0xab0
[<0>] __do_fault+0x39/0x150
[<0>] do_fault+0x25c/0x3e0
[<0>] __handle_mm_fault+0x6ca/0xc70
[<0>] handle_mm_fault+0xe9/0x350
[<0>] do_user_addr_fault+0x225/0x6c0
[<0>] exc_page_fault+0x84/0x1b0
[<0>] asm_exc_page_fault+0x27/0x30
This requires a reboot to resolve; it is a deadlock.
Note however that the call to cifs_readpage_from_fscache does mark the
page clean, but does not free the folio lock. This happens in
__cifs_readpage_from_fscache on success. Releasing the lock at that
point however is not appropriate as cifs_readahead also calls
cifs_readpage_from_fscache and *does* unconditionally release the lock
after its return. This change therefore effectively makes
cifs_readpage_worker work like cifs_readahead.
Signed-off-by: Russell Harmon <russ@xxxxxx>
Acked-by: Paulo Alcantara (SUSE) <pc@xxxxxxxxxxxxx>
Reviewed-by: David Howells <dhowells@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/cifs/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3939,9 +3939,9 @@ static int cifs_readpage_worker(struct f
io_error:
kunmap(page);
- unlock_page(page);
read_complete:
+ unlock_page(page);
return rc;
}
Patches currently in stable-queue which might be from samba-technical@xxxxxxxxxxxxxxx are
queue-4.14/cifs-release-folio-lock-on-fscache-read-hit.patch
