linux-kernel - [PATCH] drm/i915: Avoid potential sleep whilst holding spinlock

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Date:	Tue, 20 Oct 2009 17:29:16 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	intel-gfx@...ts.freedesktop.org
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.sourceforge.net,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Miles Lane <miles.lane@...il.com>
Subject: [PATCH] drm/i915: Avoid potential sleep whilst holding spinlock

Miles Lane reported the following error:
2 locks held by cat/4179:
  #0:  (&p->lock){+.+.+.}, at: [<c10a3884>] seq_read+0x25/0x315
  #1:  (&dev_priv->mm.active_list_lock){+.+...}, at: [<c119a854>]
i915_batchbuffer_info+0x2b/0x124
Pid: 4179, comm: cat Not tainted 2.6.32-rc5-git1 #2
Call Trace:
  [<c104874f>] ? __debug_show_held_locks+0x1e/0x20
  [<c1023fb0>] __might_sleep+0xf0/0xf7
  [<c101c393>] kmap+0x17/0x58
  [<c119a8d6>] i915_batchbuffer_info+0xad/0x124
  [<c10a39bf>] seq_read+0x160/0x315
  [<c108fb8c>] ? rw_verify_area+0x98/0xbb
  [<c10a385f>] ? seq_read+0x0/0x315
  [<c1090331>] vfs_read+0x75/0xa9
  [<c10903f9>] sys_read+0x3b/0x5d
  [<c1002a8f>] sysenter_do_call+0x12/0x36

The fix is relatively simple, use the atomic variants of kmap() that
avoid the potential sleep.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Miles Lane <miles.lane@...il.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 2ace8b7..9087c4c 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -268,10 +268,10 @@ static void i915_dump_pages(struct seq_file *m, struct page **pages, int page_co
 	uint32_t *mem;
 
 	for (page = 0; page < page_count; page++) {
-		mem = kmap(pages[page]);
+		mem = kmap_atomic(pages[page], KM_USER0);
 		for (i = 0; i < PAGE_SIZE; i += 4)
 			seq_printf(m, "%08x :  %08x\n", i, mem[i / 4]);
-		kunmap(pages[page]);
+		kunmap_atomic(pages[page], KM_USER0);
 	}
 }
 
-- 
1.6.5

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