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Date: Wed, 18 Nov 2009 14:23:41 +0100
From: Norbert van Bolhuis
Message-Id: <200911181323.nAIDNf94012115@linpc062.aimsys.nl>
To: linux-mtd@lists.infradead.org
Subject: [PATCH] add FAQ entry for "task pdflush:110 blocked for more than
120 seconds"
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This FAQ entry explains the possible relationship with the
warning "INFO: task pdflush:110 blocked for more than 120 seconds" and the
UBI background thread.
Signed-off-by: Norbert van Bolhuis
---
faq/ubifs.xml | 28 ++++++++++++++++++++++++++++
1 files changed, 28 insertions(+), 0 deletions(-)
diff --git a/faq/ubifs.xml b/faq/ubifs.xml
index 9a731c1..84a79d7 100644
--- a/faq/ubifs.xml
+++ b/faq/ubifs.xml
@@ -39,6 +39,7 @@
UBIFS suddenly became read-only - what is this?
I see this UBIFS error: "validate_sb: LEB size mismatch: 129024 in superblock, 126976 real"
I see this UBI error: "ubi_io_read: error -74 while reading 126976 bytes from PEB 47:4096, read 126976 bytes"
+ Is UBI/UBIFS related to this error: "INFO: task pdflush:110 blocked for more than 120 seconds"?
I want to study UBIFS - any recommendations?
@@ -1146,6 +1147,33 @@ them properly. In that case the -74
error happens when reading the
first NAND page.
+
+
+There is a known case for which the UBI background thread is related. If you are using
+NOR flash and UBI attaches to empty flash the UBI background thread will format it (only
+this way it can allow using the entire UBI volume). Formatting means that for
+each eraseblock it
+
+ - erases (very slow on NOR!)
+ - writes the UBI headers
+
+Depending on your CFI/MTD chip driver the "MTD/CFI chip lock" may be held for the time
+it needs to erase a block.
+User-space applications which manipulate files may be blocked by the UBI background thread because
+of the "MTD/CFI chip lock". This causes pdflush to block as well since it acquires the
+UBIFS journal io_mutex that the application holds. See
+this
+mail thread for details.
+There are two ways to solve this:
+
+ - ubiformat the entire NOR partition before UBI attaches
+ - use erase-suspend for writing (if your chip supports this)
+
+
+
+