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authorAndrew Morton <akpm@osdl.org>2006-06-29 05:24:26 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-29 13:26:20 -0400
commit81b0c8713385ce1b1b9058e916edcf9561ad76d6 (patch)
tree4c5e8fde3d15503c609d5c5f74911f95fc528f03
parent0686cd8fbe3e5fb1441ae84b9cbc813f9297b879 (diff)
[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>
-rw-r--r--mm/filemap.c9
-rw-r--r--mm/filemap.h4
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,
2125 break; 2125 break;
2126 } 2126 }
2127 2127
2128 if (unlikely(bytes == 0)) {
2129 status = 0;
2130 copied = 0;
2131 goto zero_length_segment;
2132 }
2133
2128 status = a_ops->prepare_write(file, page, offset, offset+bytes); 2134 status = a_ops->prepare_write(file, page, offset, offset+bytes);
2129 if (unlikely(status)) { 2135 if (unlikely(status)) {
2130 loff_t isize = i_size_read(inode); 2136 loff_t isize = i_size_read(inode);
@@ -2154,7 +2160,8 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
2154 page_cache_release(page); 2160 page_cache_release(page);
2155 continue; 2161 continue;
2156 } 2162 }
2157 if (likely(copied > 0)) { 2163zero_length_segment:
2164 if (likely(copied >= 0)) {
2158 if (!status) 2165 if (!status)
2159 status = copied; 2166 status = copied;
2160 2167
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)
88 const struct iovec *iov = *iovp; 88 const struct iovec *iov = *iovp;
89 size_t base = *basep; 89 size_t base = *basep;
90 90
91 while (bytes) { 91 do {
92 int copy = min(bytes, iov->iov_len - base); 92 int copy = min(bytes, iov->iov_len - base);
93 93
94 bytes -= copy; 94 bytes -= copy;
@@ -97,7 +97,7 @@ filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes)
97 iov++; 97 iov++;
98 base = 0; 98 base = 0;
99 } 99 }
100 } 100 } while (bytes);
101 *iovp = iov; 101 *iovp = iov;
102 *basep = base; 102 *basep = base;
103} 103}