linux-kernel - Re: [BUG] panic after umount (biscted)

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Message-ID: <20071027113916.GH8875@kernel.dk>
Date:	Sat, 27 Oct 2007 13:39:16 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Sebastian Siewior <lkml@...breakpoint.cc>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [BUG] panic after umount (biscted)

On Sat, Oct 27 2007, Sebastian Siewior wrote:
> * Jens Axboe | 2007-10-26 13:42:30 [+0200]:
> 
> >> [2] http://download.breakpoint.cc/bug/bug_rc1_patch_reboot.jpeg 171 KiB
> >
> >Ah, second BUG() for same issue. Try this one. This?
> >
> >diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> >index 61fdaf0..57fde7b 100644
> >--- a/drivers/scsi/scsi_lib.c
> >+++ b/drivers/scsi/scsi_lib.c
> >@@ -1115,6 +1115,8 @@ static int scsi_init_io(struct scsi_cmnd *cmd)
> > 	 * kmapping pages)
> > 	 */
> > 	cmd->use_sg = req->nr_phys_segments;
> >+	if (!cmd->use_sg)
> >+		return 0;
> > 
> > 	/*
> > 	 * If sg table allocation fails, requeue request later.
> >@@ -1191,7 +1193,7 @@ int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
> > 	if (req->bio) {
> > 		int ret;
> > 
> >-		BUG_ON(!req->nr_phys_segments);
> >+		BUG_ON(!req->nr_phys_segments && req->bio->bi_size);
> > 
> > 		ret = scsi_init_io(cmd);
> > 		if (unlikely(ret))
> >@@ -1236,9 +1238,10 @@ int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
> > 	if (ret != BLKPREP_OK)
> > 		return ret;
> > 	/*
> >-	 * Filesystem requests must transfer data.
> >+	 * Filesystem requests must transfer data, unless it's an empty
> >+	 * barrier.
> > 	 */
> >-	BUG_ON(!req->nr_phys_segments);
> >+	BUG_ON(!req->nr_phys_segments && !bio_empty_barrier(req->bio));
> > 
> > 	cmd = scsi_get_cmd_from_req(sdev, req);
> > 	if (unlikely(!cmd))
> >
> 
> I'm afraid you did not make it to the next level. I hope you have
> another man :). [1] shows the result. I double checked it, it seems to
> be the same bug() with the second patch.
> 
> [1] http://download.breakpoint.cc/bug/bug_patch2.jpeg 134 KiB

OK, can you see what this produces?

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 61fdaf0..4042269 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1115,6 +1115,8 @@ static int scsi_init_io(struct scsi_cmnd *cmd)
 	 * kmapping pages)
 	 */
 	cmd->use_sg = req->nr_phys_segments;
+	if (!cmd->use_sg)
+		return 0;
 
 	/*
 	 * If sg table allocation fails, requeue request later.
@@ -1191,7 +1193,7 @@ int scsi_setup_blk_pc_cmnd(struct scsi_device *sdev, struct request *req)
 	if (req->bio) {
 		int ret;
 
-		BUG_ON(!req->nr_phys_segments);
+		BUG_ON(!req->nr_phys_segments && req->bio->bi_size);
 
 		ret = scsi_init_io(cmd);
 		if (unlikely(ret))
@@ -1236,9 +1238,11 @@ int scsi_setup_fs_cmnd(struct scsi_device *sdev, struct request *req)
 	if (ret != BLKPREP_OK)
 		return ret;
 	/*
-	 * Filesystem requests must transfer data.
+	 * Filesystem requests must transfer data, unless it's an empty
+	 * barrier.
 	 */
-	BUG_ON(!req->nr_phys_segments);
+	if (!req->nr_phys_segments && !bio_empty_barrier(req->bio))
+		blk_dump_rq_flags(req, "scsi");
 
 	cmd = scsi_get_cmd_from_req(sdev, req);
 	if (unlikely(!cmd))

-- 
Jens Axboe

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