4.16-stable review patch. If anyone has any objections, please let me know.
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From: Amir Goldstein amir73il@gmail.com
[ Upstream commit 19b9ad67310ed2f685062a00aec602bec33835f0 ]
The comment claims that this helper will try not to loose bits, but for 64bit long it looses the high bits before hashing 64bit long into 32bit int. Use the helper hash_long() to do the right thing for 64bit long. For 32bit long, there is no change.
All the callers of end_name_hash() either assign the result to qstr->hash, which is u32 or return the result as an int value (e.g. full_name_hash()). Change the helper return type to int to conform to its users.
[ It took me a while to apply this, because my initial reaction to it was - incorrectly - that it could make for slower code.
After having looked more at it, I take back all my complaints about the patch, Amir was right and I was mis-reading things or just being stupid.
I also don't worry too much about the possible performance impact of this on 64-bit, since most architectures that actually care about performance end up not using this very much (the dcache code is the most performance-critical, but the word-at-a-time case uses its own hashing anyway).
So this ends up being mostly used for filesystems that do their own degraded hashing (usually because they want a case-insensitive comparison function).
A _tiny_ worry remains, in that not everybody uses DCACHE_WORD_ACCESS, and then this potentially makes things more expensive on 64-bit architectures with slow or lacking multipliers even for the normal case.
That said, realistically the only such architecture I can think of is PA-RISC. Nobody really cares about performance on that, it's more of a "look ma, I've got warts^W an odd machine" platform.
So the patch is fine, and all my initial worries were just misplaced from not looking at this properly. - Linus ]
Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/stringhash.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/include/linux/stringhash.h +++ b/include/linux/stringhash.h @@ -50,9 +50,9 @@ partial_name_hash(unsigned long c, unsig * losing bits). This also has the property (wanted by the dcache) * that the msbits make a good hash table index. */ -static inline unsigned long end_name_hash(unsigned long hash) +static inline unsigned int end_name_hash(unsigned long hash) { - return __hash_32((unsigned int)hash); + return hash_long(hash, 32); }
/*