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author | Andrew Morton <akpm@osdl.org> | 2006-06-29 02:24:26 -0700 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-06-29 10:26:20 -0700 |
commit | 81b0c8713385ce1b1b9058e916edcf9561ad76d6 (patch) | |
tree | 4c5e8fde3d15503c609d5c5f74911f95fc528f03 /mm | |
parent | 0686cd8fbe3e5fb1441ae84b9cbc813f9297b879 (diff) | |
download | linux-stable-81b0c8713385ce1b1b9058e916edcf9561ad76d6.tar.gz linux-stable-81b0c8713385ce1b1b9058e916edcf9561ad76d6.tar.bz2 linux-stable-81b0c8713385ce1b1b9058e916edcf9561ad76d6.zip |
[PATCH] generic_file_buffered_write(): handle zero-length iovec segments
The recent generic_file_write() deadlock fix caused
generic_file_buffered_write() to loop inifinitely when presented with a
zero-length iovec segment. Fix.
Note that this fix deliberately avoids calling ->prepare_write(),
->commit_write() etc with a zero-length write. This is because I don't trust
all filesystems to get that right.
This is a cautious approach, for 2.6.17.x. For 2.6.18 we should just go ahead
and call ->prepare_write() and ->commit_write() with the zero length and fix
any broken filesystems. So I'll make that change once this code is stabilised
and backported into 2.6.17.x.
The reason for preferring to call ->prepare_write() and ->commit_write() with
the zero-length segment: a zero-length segment _should_ be sufficiently
uncommon that this is the correct way of handling it. We don't want to
optimise for poorly-written userspace at the expense of well-written
userspace.
Cc: "Vladimir V. Saveliev" <vs@namesys.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Greg KH <greg@kroah.com>
Cc: <stable@kernel.org>
Cc: walt <wa1ter@myrealbox.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/filemap.c | 9 | ||||
-rw-r--r-- | mm/filemap.h | 4 |
2 files changed, 10 insertions, 3 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 4082b3b3cea7..648f2c0c8e18 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2125,6 +2125,12 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, break; } + if (unlikely(bytes == 0)) { + status = 0; + copied = 0; + goto zero_length_segment; + } + status = a_ops->prepare_write(file, page, offset, offset+bytes); if (unlikely(status)) { loff_t isize = i_size_read(inode); @@ -2154,7 +2160,8 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, page_cache_release(page); continue; } - if (likely(copied > 0)) { +zero_length_segment: + if (likely(copied >= 0)) { if (!status) status = copied; diff --git a/mm/filemap.h b/mm/filemap.h index 536979fb4ba7..3f2a343c6015 100644 --- a/mm/filemap.h +++ b/mm/filemap.h @@ -88,7 +88,7 @@ filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes) const struct iovec *iov = *iovp; size_t base = *basep; - while (bytes) { + do { int copy = min(bytes, iov->iov_len - base); bytes -= copy; @@ -97,7 +97,7 @@ filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes) iov++; base = 0; } - } + } while (bytes); *iovp = iov; *basep = base; } |