The patch titled
fix-pagecache-write-deadlocks
has been removed from the -mm tree. Its filename is
fix-pagecache-write-deadlocks.patch
This patch was dropped because it is obsolete
------------------------------------------------------
Subject: fix-pagecache-write-deadlocks
From: Andrew Morton <akpm@xxxxxxxx>
This is half-written and won't work.
The idea is to modify the core write() code so that it won't take a pagefault
while holding a lock on the pagecache page.
- Instead of copy_from_user(), use inc_preempt_count() and
copy_from_user_inatomic().
- If the copy_from_user_inatomic() hits a pagefault, it'll return a short
copy.
- So zero out the remainder of the pagecache page (the uncopied bit).
- but only if the page is not uptodate.
- commit_write()
- unlock_page()
- adjust various pointers and counters
- go back and try to fault the page in again, redo the lock_page,
prepare_write, copy_from_user_inatomic(), etc.
- After a certain number of retries, someone is being silly: give up.
Now, the design objective here isn't just to fix the deadlock. It's to be
able to copy multiple iovec segments into the pagecache page within a single
prepare-write/commit_write pair. But to do that, we'll need to prefault them.
That could get complex. Walk across the segments, touching each user page
until we reach the point where we see that this iovec segment doesn't fall
into the target page.
Alternatively, only prefault the *present* iovec segment. The code as
designed will handle pagefaults against the user's pages quite happily. But
is it efficient? Needs thought.
(I think we will end up with quite a bit of dead code as a reault of this
exercise - some of the fancy user-copying inlines. Needs checking when the
dust has settled).
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
mm/filemap.c | 7 ++--
mm/filemap.h | 69 ++++++++++++++++++++++++++++++++++---------------
2 files changed, 53 insertions(+), 23 deletions(-)
diff -puN mm/filemap.c~fix-pagecache-write-deadlocks mm/filemap.c
--- a/mm/filemap.c~fix-pagecache-write-deadlocks
+++ a/mm/filemap.c
@@ -2133,11 +2133,12 @@ generic_file_buffered_write(struct kiocb
break;
}
if (likely(nr_segs == 1))
- copied = filemap_copy_from_user(page, offset,
+ copied = filemap_copy_from_user_atomic(page, offset,
buf, bytes);
else
- copied = filemap_copy_from_user_iovec(page, offset,
- cur_iov, iov_offset, bytes);
+ copied = filemap_copy_from_user_iovec_atomic(page,
+ offset, cur_iov, iov_offset,
+ bytes);
flush_dcache_page(page);
status = a_ops->commit_write(file, page, offset, offset+bytes);
if (status == AOP_TRUNCATED_PAGE) {
diff -puN mm/filemap.h~fix-pagecache-write-deadlocks mm/filemap.h
--- a/mm/filemap.h~fix-pagecache-write-deadlocks
+++ a/mm/filemap.h
@@ -22,19 +22,19 @@ __filemap_copy_from_user_iovec_inatomic(
/*
* Copy as much as we can into the page and return the number of bytes which
- * were sucessfully copied. If a fault is encountered then clear the page
- * out to (offset+bytes) and return the number of bytes which were copied.
+ * were sucessfully copied. If a fault is encountered then return the number of
+ * bytes which were copied.
*
- * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache
- * to *NOT* zero any tail of the buffer that it failed to copy. If it does,
- * and if the following non-atomic copy succeeds, then there is a small window
- * where the target page contains neither the data before the write, nor the
- * data after the write (it contains zero). A read at this time will see
- * data that is inconsistent with any ordering of the read and the write.
- * (This has been detected in practice).
+ * NOTE: For this to work reliably we really want
+ * copy_from_user_inatomic_nocache to *NOT* zero any tail of the buffer that it
+ * failed to copy. If it does, and if the following non-atomic copy succeeds,
+ * then there is a small window where the target page contains neither the data
+ * before the write, nor the data after the write (it contains zero). A read at
+ * this time will see data that is inconsistent with any ordering of the read
+ * and the write. (This has been detected in practice).
*/
static inline size_t
-filemap_copy_from_user(struct page *page, unsigned long offset,
+filemap_copy_from_user_atomic(struct page *page, unsigned long offset,
const char __user *buf, unsigned bytes)
{
char *kaddr;
@@ -53,14 +53,28 @@ filemap_copy_from_user(struct page *page
return bytes - left;
}
+static inline size_t
+filemap_copy_from_user_nonatomic(struct page *page, unsigned long offset,
+ const char __user *buf, unsigned bytes)
+{
+ int left;
+ char *kaddr;
+
+ kaddr = kmap(page);
+ left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
+ kunmap(page);
+ return bytes - left;
+}
+
/*
- * This has the same sideeffects and return value as filemap_copy_from_user().
+ * This has the same sideeffects and return value as
+ * filemap_copy_from_user_atomic().
* The difference is that on a fault we need to memset the remainder of the
* page (out to offset+bytes), to emulate filemap_copy_from_user()'s
* single-segment behaviour.
*/
static inline size_t
-filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
+filemap_copy_from_user_iovec_atomic(struct page *page, unsigned long offset,
const struct iovec *iov, size_t base, size_t bytes)
{
char *kaddr;
@@ -70,14 +84,29 @@ filemap_copy_from_user_iovec(struct page
copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
base, bytes);
kunmap_atomic(kaddr, KM_USER0);
- if (copied != bytes) {
- kaddr = kmap(page);
- copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
- base, bytes);
- if (bytes - copied)
- memset(kaddr + offset + copied, 0, bytes - copied);
- kunmap(page);
- }
+ return copied;
+}
+
+/*
+ * This has the same sideeffects and return value as
+ * filemap_copy_from_user_nonatomic().
+ * The difference is that on a fault we need to memset the remainder of the
+ * page (out to offset+bytes), to emulate filemap_copy_from_user_nonatomic()'s
+ * single-segment behaviour.
+ */
+static inline size_t
+filemap_copy_from_user_iovec_nonatomic(struct page *page, unsigned long offset,
+ const struct iovec *iov, size_t base, size_t bytes)
+{
+ char *kaddr;
+ size_t copied;
+
+ kaddr = kmap(page);
+ copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
+ base, bytes);
+ if (bytes - copied)
+ memset(kaddr + offset + copied, 0, bytes - copied);
+ kunmap(page);
return copied;
}
_
Patches currently in -mm which might be from akpm@xxxxxxxx are
revert-pci-quirk-for-ibm-dock-ii-cardbus-controllers.patch
ioc4-fixes.patch
ioc4-kconfig-fix.patch
remove_mapping-fix.patch
proc_numbuf-is-wrong.patch
carta_random32-fix-linkage.patch
rename-net_random-to-random32-fixes.patch
rename-net_random-to-random32-fix-2.patch
vmalloc-dont-pass-__gfp_zero-to-slab.patch
fix-build-breakage-with-config_ppc32-fix.patch
revert-generic_file_buffered_write-handle-zero-length-iovec-segments.patch
revert-generic_file_buffered_write-deadlock-on-vectored-write.patch
generic_file_buffered_write-cleanup.patch
mm-fix-pagecache-write-deadlocks.patch
fix-pagecache-write-deadlocks.patch
git-acpi.patch
i386-acpi-build-fix.patch
acpi-asus-s3-resume-fix.patch
sony_apci-resume.patch
git-dvb-build-fix.patch
git-infiniband.patch
git-input.patch
git-input-fixup.patch
git-libata-all.patch
mtd-maps-support-for-bios-flash-chips-on-intel-esb2-southbridge.patch
git-netdev-all.patch
libphy-dont-do-that.patch
drivers-net-ns83820c-add-paramter-to-disable-auto.patch
git-pcmcia-fixup.patch
git-serial-fixup.patch
git-scsi-target-fixup.patch
git-scsi-target-vs-git-block.patch
fix-gregkh-usb-usbatm-fix-tiny-race.patch
xpad-dance-pad-support.patch
git-watchdog.patch
x86_64-dump_trace-atomicity-fix.patch
spinlock-debug-all-cpu-backtrace.patch
xfs-rename-uio_read.patch
touchkit-ps-2-touchscreen-driver.patch
get-rid-of-zone_table.patch
new-scheme-to-preempt-swap-token-tidy.patch
radix-tree-rcu-lockless-readside.patch
acx1xx-wireless-driver.patch
swsusp-add-resume_offset-command-line-parameter-rev-2.patch
deprecate-smbfs-in-favour-of-cifs.patch
edac-new-opteron-athlon64-memory-controller-driver.patch
add-address_space_operationsbatch_write.patch
kbuild-dont-put-temp-files-in-the-source-tree.patch
lockdep-annotate-nfs-nfsd-in-kernel-sockets-tidy.patch
bug-test-1.patch
log2-implement-a-general-integer-log2-facility-in-the-kernel-fix.patch
fs-cache-provide-a-filesystem-specific-syncable-page-bit-ext4.patch
fs-cache-make-kafs-use-fs-cache-fix.patch
fs-cache-make-kafs-use-fs-cache-vs-streamline-generic_file_-interfaces-and-filemap.patch
nfs-use-local-caching-12-fix.patch
fs-cache-cachefiles-a-cache-that-backs-onto-a-mounted-filesystem-log2-fix.patch
swap_prefetch-vs-zoned-counters.patch
readahead-sysctl-parameters.patch
make-copy_from_user_inatomic-not-zero-the-tail-on-i386-vs-reiser4.patch
make-kmem_cache_destroy-return-void-reiser4.patch
reiser4-hardirq-include-fix.patch
reiser4-run-truncate_inode_pages-in-reiser4_delete_inode.patch
reiser4-get_sb_dev-fix.patch
reiser4-vs-zoned-allocator.patch
reiser4-rename-generic_sounding_globalspatch-fix.patch
hpt3xx-rework-rate-filtering-tidy.patch
gtod-persistent-clock-support-i386.patch
hrtimers-state-tracking.patch
clockevents-drivers-for-i386.patch
gtod-mark-tsc-unusable-for-highres-timers.patch
round_jiffies-infrastructure-fix.patch
kevent-core-files-fix.patch
kevent-core-files-s390-hack.patch
kevent-socket-notifications-fix-2.patch
kevent-socket-notifications-fix-4.patch
kevent-timer-notifications-fix.patch
nr_blockdev_pages-in_interrupt-warning.patch
device-suspend-debug.patch
mutex-subsystem-synchro-test-module-fix.patch
slab-leaks3-default-y.patch
x86-kmap_atomic-debugging.patch
restore-rogue-readahead-printk.patch
put_bh-debug.patch
acpi_format_exception-debug.patch
warn-if-setting-non-uptodate-page-dirty.patch
jmicron-warning-fix.patch
squash-ipc-warnings.patch
squash-udf-warnings.patch
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