On Wed, 22 Aug 2018, Jens Axboe wrote:
> On 8/22/18 10:23 AM, Mikulas Patocka wrote:
> > It is possible to call fsync on a read-only handle (for example, fsck.ext2
> > does it when doing read-only check), and this call results in kernel
> > warning. This bug was introduced by the commit 721c7fc701c7 "block: fail
> > op_is_write() requests to read-only partitions".
>
> Similar patch is already queued up, it'll go into Linus's tree before
> -rc1.
>
> --
> Jens Axboe
I think you mean the patch b089cfd95d32638335c551651a8e00fd2c4edb0b, but
it doesn't work.
The first problem is that bio_op returns the opcode, but op_is_flush
expects flags as its parameter. bio_op strips off the flags, and so the
condition op_is_flush is never true and the warning is not shut off.
Anoher problem is that the flags REQ_FUA and REQ_PREFLUSH may be
superimposed on regular write bio and in that case the warning should be
triggered. We want to shut the warning off only if bio_sectors is zero
(i.e. if the flush request is not superimposed on regular write).
Mikulas
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Subject: [PATCH] block: don't warn when doing fsync on read-only devices
It is possible to call fsync on a read-only handle (for example, fsck.ext2
does it when doing read-only check), and this call results in kernel
warning.
The patch b089cfd95d32 ("block: don't warn for flush on read-only device")
attempted to disable the warning, but it is buggy and it doesn't
(op_is_flush tests flags, but bio_op strips off the flags).
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Fixes: 721c7fc701c7 ("block: fail op_is_write() requests to read-only partitions")
Cc: stable@xxxxxxxxxxxxxxx # 4.18
---
block/blk-core.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c 2018-09-03 23:32:38.550000000 +0200
+++ linux-2.6/block/blk-core.c 2018-09-03 23:33:11.960000000 +0200
@@ -2163,9 +2163,12 @@ static inline bool bio_check_ro(struct b
{
const int op = bio_op(bio);
- if (part->policy && (op_is_write(op) && !op_is_flush(op))) {
+ if (part->policy && op_is_write(op)) {
char b[BDEVNAME_SIZE];
+ if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
+ return false;
+
WARN_ONCE(1,
"generic_make_request: Trying to write "
"to read-only block-device %s (partno %d)\n",
